Hybrid composite of gold nanoparticles with polyacrylamide hydrogel: one-step synthesis, preparation of plasmon films, characterization

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In our study we have (1) proposed a one-step method for the synthesis of a hybrid composite of Au NPs with polyacrylamide hydrogel (PAAm) by the reduction of HAuCl 4 with acrylamide (AAm) and simultaneous radical polymerization of AAm in an aqueous solution, (2) optimized the conditions for obtaining a phase-stable product, (3) studied the effect of the initial concentrations of Au and AAm on the morphology and structure of Au NPs, (4) obtained and characterized plasmonic films from the Au NPs-PAAm composite and after thermal removal of the polymer matrix. The methods of UV-visible and photon correlation spectroscopy, X-ray diffraction, synchronous thermal analysis, transmission and scanning electron microscopy were used in the work. Graphical abstract hybrid composite gold nanoparticles polyacrylamide hydrogel Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 Figure 14 Figure 15 Highlights A hybrid composite of gold nanoparticles with polyacrylamide hydrogel was synthesized by a one-pot, one-step method from H[AuCl 4 ] and acrylamide Optimal conditions for the synthesis of a stable product are initial concentrations of 3 mM for gold and 1 M for acrylamide, temperature 60°C Using a composite hydrogel on glass, films of a dry composite of gold nanoparticles with polyacrylamide were obtained by dehydration at 100°C and thin gold after heating at 550°C Surface plasmon resonance bands in the spectra of the synthesized hybrid composite hydrogel and of films have favorable for use in optical sensing well-defined maxima in the wavelength range 570-600 nm 1 Introduction Nanoparticles (NPs) are of great importance for modern science and technology. Nor sole NPs but their ensembles are significant for their practical use [ 1 , 2 ], either in liquid media (solvents or solutions), in solid matrices (polymers, glasses, ceramics), or in the form of 1–2D-structures in fibers and on surfaces (layers, films). Combinations of NPs with matrices form nanocomposites, which are hybrid if the matrices are based on organic or biological polymers. Hybrid nanocomposites composed of plasmon metal NPs of Au (or Ag), distributed in semi-solid (soft) matrices of polymer hydrogels attract special attention [ 3 ]. Unlike composites with solid matrices possessing fixed static properties, hybrid gel composites open the way to dynamic materials allowing controllable changes of properties and responses to various external chemical, physical or mechanical actions (stimuli) [ 3 – 5 ]. These composite materials not only combine the properties of structured NPs ensembles and matrices but also gain some new functions [ 1 , 5 ]. Due to the local surface plasmon resonance (SPR) arising in nanometer-sized metal particles under the action of light, Au NPs are able to absorb, concentrate, scatter, redistribute and transform (convert) photon energy [ 3 , 6 – 8 ]. In this respect, Au NPs in hybrid composites may act as optical sensors (probes) for reagents and media [ 2 , 3 , 7 – 10 ], substrates for SERS [ 3 , 5 , 9 ], contrast agents for visualization of nano- and micrometer-sized objects [ 2 , 3 , 8 ], optical filters [ 9 ], as photocatalytic and photothermal triggers of physicochemical and mechanical processes at the micro level [ 2 , 3 , 8 , 12 ]. In addition, they may serve as light guides due to plasmon interactions [ 1 , 6 , 8 , 10 ], and render electrical conduction to materials due to the metal nature of the cores [ 11 ]. It is essential that gold is not toxic, biocompatible [ 4 ] and possesses high affinity to DNA [ 12 ]. In turn, polymer hydrogels, which are polymer networks cross-linked through covalent bridges or/and labile bonds (hydrogen, molecular) and are able to absorb and retain water reversibly in the amount up to 99% of the mass of hydrogel [ 13 , 14 ], act in hybrid composites as a matrix medium providing dispersity and stability of the structured NPs ensemble [ 5 ]. In addition, they may, in particular after additional modifications, function as smart materials that respond to the action of various stimuli (light, temperature, solvent, pH, chemical reagents, physical deformation) reversibly changing their volume and structure, switching gel/solution or gel/solid states, and self-restoring [ 15 – 18 ]. Hydrogels described in publications are based on polyaniline [ 14 ], cellulose [ 18 , 19 ], DNA [ 8 , 12 ], polyanhydride (polifeprosan 20) [ 20 ], organosilicon polymers [ 7 , 9 ]. Many studies deal with the hydrogels based on the derivatives of polyacrylamide (PAAm) [ 15 – 17 , 21 ] and their composites with Au NPs [ 2 , 4 , 5 , 10 , 22 ]. High hydration degree and three-dimensional network-type structure render polymer hydrogels similarity and compatibility with biological tissues of living organisms [ 13 , 14 ], and Au NPs are also biocompatible, as mentioned above, so the application potential of hybrid Au NPs composites with the hydrogels of PAAm and its derivatives is first of all directed towards medicine. Possible application areas include theranostics, photoacoustic visualization, and photothermal therapy [ 2 ], drug transport, molecular recognition, chemical valves and chemical-mechanical energy transformation, artificial tissues/muscles [ 4 ], compact sensitive sensor devices [ 10 ], controllable photoinduced drug release [ 22 ]. It should also be stressed that polyacrylamide hydrogel is well suitable for developing microstructures with high spatial resolution using already refined methods, for example soft lithography [ 23 ], which is essential for the application of composite gels in working devices. Four approaches to obtaining hybrid polymeric nanocomposites are known: 1) the formation of a polymeric matrix in NPs suspension, 2) inclusion of NPs into preliminarily formed polymer matrix, 3) in situ synthesis of NPs in the preliminarily formed polymer, and 4) the formation of polymeric matrix promoted by functionalized NPs [ 3 ]. With all these approaches, the synthesis is relatively complex and multi-step. In our work, we tested the approach based on the simultaneous synthesis of Au NPs and PAAm from a mixture of precursors, which are HAuCl 4 and acrylamide (AAm). The objectives of our investigation were: 1) to test the possibility of the single-stage synthesis of a hybrid composite of Au NPs with PAAm hydrogel through HAuCl 4 reduction with acrylamide and simultaneous radical polymerization of AAm, initiated by ammonium persulfate, in the aqueous solution; 2) to optimize the conditions for obtaining phase-stable product, with respect to the initial concentrations of Au and AAm; 3) to study the effect of concentration-related synthesis conditions on the morphology and structure of Au NPs; 4) to obtain the plasmon films from the solid composite of Au NPs/PAAm and after thermal removal of the polymer matrix, and to characterize these films. 2 Experimental The chemicals used in the work were HAuCl 4 · x H 2 O preparation obtained from metal gold (wire) according to a generally accepted procedure [ 24 ] and the following reagents: acrylamide for electrophoresis (> 99.0%, specially pure reagent grade, Medigen), ammonium persulfate (98%, reagent grade, Sigma-Aldrich). To synthesize a hybrid composite of Au NPs with PAAm hydrogel, weighed portions of crystal HAuCl 4 ∙ x H 2 O and AAm powder, placed in one vessel, were poured with an aqueous solution of 1.2 mM (NH 4 ) 2 S 2 O 8 , heated to the desired temperature (55°, 60°, or 65°C), which was the initiator of radical polymerization of AAm. The mixture was stirred until the solid components dissolved. The reaction mixture was kept in a closed vessel for 6 hours in a drying box at the selected temperature. In kinetic experiments, the mixture was pored into a thermostated spectrophotometric cell to record the changes in the UV-vis spectrum during the synthesis. The substrates for making the films were square, 25×25×1 mm in size, cut from microscopic slides (Heinz Herenz, Germany). Substrate preparation included the treatment in an ultrasonic bath for 10 min in the 2% aqueous solution of Fairy detergent, washing with distilled water, exposure in a mixture of concentrated H 2 SO 4 and H 2 O 2 (3:1), washing with deionized water, drying in the air in the drying box at 100°C. The films were deposited by spin-coating. The deposition cycle proceeded as follows: a portion of the gel was dropped into the center of the substrate, spinning was turned on and continued at the fixed spin rate (ω) for the necessary time interval ( t , relatively long because of the high viscosity of the gel), and dried in the air at 100°C. To form the film, the deposition cycle was repeated as many times as necessary (n). Drying caused the formation of a solid composite film of Au NPs and PAAm, while subsequent heating at 550°C resulted in the formation of an isle-type thin gold film. The UV-vis spectra of solutions were recorded with respect to water, and films with respect to pure substrates, with the help of Shimadzu UV-1700 spectrophotometer. The average hydrodynamic diameter of the polymer globules of PAAm in hydrogels ( d PAAm ) was measured by means of photon-correlation spectroscopy at an angle of 90° in the quartz cell with the section of 1×1 cm at room temperature using a 90Plus spectrometer (Brookhaven Inst). Averaging was carried out over the number of particles within the hypothesis of lognormal distribution. X-ray diffraction investigation of Au NPs in hydrogels and in dried products was carried out using an X-ray diffractometer Bruker D8 Venture (microfocus tube Incoatec 1µS 3.0 Cu, detector PHOTON 3, resolution 768×1024, D = 60 mm, 2θ D = − 40°). The samples were prepared as follows. A drop of hydrogel with Au NPs was deposited onto a slide, and a piece with linear size ~ 0.3 mm was cut off the surface after drying. For sample No. 2, Si powder (SRM 640a, a = 5.430593 Å) was added into the gel to be used further on as an internal standard. The samples were fixed on the goniometer head, centered, and examination was carried out using Debye-Scherrer scheme. The Debye-Scherrer powder patterns were recorded in the mode with the sample completing the turn around the axis φ for 10–30 min. The introduction of corrections for the reference and the transition to the standard form I(2θ) were performed using the DIOPTAS software [ 25 ]. To determine the size of coherent scattering regions (CSR) with the POWDER CELL software [ 26 ], the full-profile refinement was carried out (using pseudo-Voigt function) within the angle range from 42.8° to 46.0°2θ, where the (200) Au reflection was located. Broadening (Δ) of this reflection was calculated with respect to (220) Si (FWHM = 0.332°2θ). Synchronous thermal analysis (STA) was performed using an STA 449F1 Jupiter® instrument (Germany) within the temperature range 30°-1200°C in the atmosphere of synthetic air at the gas flow rate of argon 40 mL/min and oxygen 10 mL/min with the heating rate of 10 o C/min. Closed crucibles made of Al 2 O 3 were used. The reference sample was an empty crucible with a cap. Experimental data were treated using the Proteus analysis software package. 3 Results and discussion 3.1 Synthesis of the hybrid composite The composite of Au NPs with PAAm hydrogel was obtained by conducting two parallel processes simultaneously in the aqueous solution: synthesis of gold NPs through the reduction of [AuCl 4 ] – by the olefin fragment of AAm, and the radical polymerization of AAm. The possibility of these processes to take place was separately determined previously [ 27 , 28 ]. The UV spectroscopic investigation within the range of 300–1000 nm allowed us to observe the formation of Au NPs, while other components did not absorb the light at wavelengths longer than 350 nm. The appearance and enhancement of extinction (light absorption + scattering) in the region of ~ 550 and > 650 nm was due to the bands associated with individual and collective SPR of the growing Au NPs (Fig. 1 a). Particle formation was not fast, and it continued after 6-hours long heating stopped, which was confirmed by the spectrum recorded 4 days later. The same was confirmed by the spectra of synthesis products, recorded after heating for 6 hours at different temperatures (Fig. 1 b), and by the behavior of kinetic curves at fixed wavelengths (Fig. 1 c,d). The higher was temperature, the higher was the intensity of spectrum, and therefore the process extent. Kinetic curves at the wavelength of 775 nm in the region of collective SPR exhibited the induction period because the interaction between particles and the collective resonance caused by this interaction emerged not immediately but while the particles were accumulated and grew. Table 1 presents the conditions under which the samples of composite hydrogels were obtained for the purpose of revealing the effect of initial concentrations of gold and acrylamide. Not all these products were homogeneous hydrogels; depending on с AAm and с Au , some samples exhibited insufficient phase stability, and Au NPs were partially or almost completely separated in the form of precipitate. Table 1 The studied samples of composite hydrogels: No., obtaining conditions ( c (NH4)2S2O8 =1.2 mM, 60°C), the presence of precipitates No. с Au , mM с AAm , M Precipitate 1 0.26 1 – 2 0.26 0.5 – 3 0.26 0.26 + 4 0.26 0.1 + 5 10 1 + 6 3 1 – 7 1 1 – 8 3 1 – 9 3 0.5 + 3.2 Effect of acrylamide concentration With an increase in initial AAm concentration, we observed an increase in the viscosity of the formed polymer hydrogels and the average hydrodynamic diameter of PAAm globules – d PAAm = 49 ± 6 nm ( с AAm =0.25 M), 94 ± 13 nm (0.5 M), and 158 ± 32 nm (1 M). With the fixed gold concentration с Au =0.26 mM, homogeneous and storage-stable for 1 month were the products for acrylamide concentration с AAm =1 and 0.5 M, while for с AAm =0.26 and 0.1 M the precipitate of Au NPs was present (Table 1 ). Comparison of the spectra of products immediately after the synthesis during heating and a month later, after storage under usual conditions (Fig. 2 ), allows us to assume the following. The stability of products in the case of high с AAm concentrations may be explained by higher acrylamide polymerization rate with respect to the rate of Au NP formation, as well as by the higher viscosity of gel matrix with NPs. The gel medium affected also the rate of Au NPs formation: in the medium with higher viscosity, for с AAm =1 M, the intensity of spectrum related to the synthesis product was initially lower (therefore, the extent of NPs formation was lower) than the intensity of product spectrum at с AAm =0.5 M, other synthesis conditions being equal (Fig. 2 a,b). A month later, the intensities of the spectra approached each other due to complete recovery and [AuCl 4 ] – transformation into Au NPs. In this situation, the intensity of individual SPR band of the particles at ~ 540 nm was higher for the product with the matrix possessing higher viscosity, while the intensity of the band of collective SPR within the range of ~ 760–780 nm was higher for the product with less viscous matrix. In the case of low acrylamide concentration с AAm , the intensity of spectra was initially low, especially for с AAm =0.1 M (Fig. 2 c,d), and a month later it dropped almost to zero because of Au NPs sedimentation. 3.3 Effect of gold concentration The effect of gold concentration at the constant acrylamide concentration с AAm =1 M is illustrated by product spectra presented in Fig. 3 . The best result was obtained for с Au =3 mM (Fig. 3 b): the product was stable, its spectrum reached its maximal limiting intensity during heating at 60°С for 6 hours, remained unchanged further on, and contained a clearly pronounced SPR band related to individual NPs. At с Au =10 and 1 mM, NPs coagulation and precipitation occurred, almost complete in the case of 10 mM Au (Fig. 3 a,c). At с Au =0.26 mM, the process of Au NPs formation continued for a long time after 6-hour long heating was finished (Fig. 3 d). So, the following conditions were chosen as optimal for the synthesis of stable hybrid composite of Au NPs with PAAm hydrogel: с Au =3 mM, с AAm =1 M, c (NH4)2S2O8 =1.2 mM, temperature 60°C, heating time 6 hours. The product obtained under these conditions was a transparent thick gel, violet in transmitted light and brown in reflected light. Synthesis result was steadily reproduced in independent experiments (Fig. 4 ). 3.4 X-ray investigation Investigation of the products presented in Tables 1 and 2 revealed the presence of gold as the only crystal phase (Fig. 5 ). Sample No. 1 of composite hydrogel, synthesized at с Au =0.26 mM and с AAm =1 M, turned out to be X-ray amorphous, in other cases the size of CSR was estimated for Au NPs. The obtained values, along with the positions of maxima and the full width at half-maximum (FWHM), are shown in Table 2 . Under the optimal synthesis conditions ( с Au =3 mM, с AAm =1 M), CSR size for gold in NPs was 20–22 nm (samples Nos. 6 and 8). A decrease in с AAm from 1 to 0.1 M at the fixed low gold concentration с Au =0.26 mM caused an increase in CSR size: No. 1 – amorphous, No. 4–18 nm. For higher gold concentration ( с Au =3 mM), a decrease in с AAm from 1 to 0.5 M caused a slight increase in CSR size from 20 (No. 8) to 23 (No. 9). For the fixed acrylamide concentration с AAm =1 M, an increase in gold concentration с Au from 0.26 to 3 and then to 10 mM caused a substantial increase in CSR size up to 87 nm (No. 5). At constant с AAm =0.5 M, an increase in с Au from 0.26 to 3 mM caused an increase in CSR size from 10 (No. 2) to 23 nm (No. 9). Table 2 Results of the treatment of (200) Au reflection profile in the diffraction patterns of gel and precipitate samples No. 2θ (200), ° FWHM (200), ° Δ a , ° CSR, nm 1 b – – – – 2 44.29 1.303 0.971 10 3 44.31 1.215 0.883 11 c 4 44.29 0.867 0.535 18 c 5 44.33 0.442 0.110 87 c 6 44.29 0.771 0.439 22 7 44,29 0.908 0.576 17 8 44.29 0.809 0.477 20 9 44.31 0.741 0.409 23 a with respect to the (220) Si line (FWHM = 0.332°2θ); b amorphous; c for precipitate 3.5 Transmission electron microscopy The TEM images of X-ray amorphous product No. 1 revealed the presence of isometric particles (Fig. 6 ), the size of cross sections varies from 21 to 31 nm; the average value is d = 24.5 ± 1.2 nm (size distribution is shown in the insert to Fig. 6 ). It may be assumed that there is a gel layer between NPs. In the product No. 8, obtained under optimal conditions ( с Au =3 mM and с AAm =1 M), NPs of different shapes are observed: spheroids, cubes and bars (Fig. 7 ). Spheroid particles (Fig. 7 a) are up to ~ 102 nm in size and are composed of small crystallites (according to estimations, the size of CSR is 20 nm). Cubes and bars look like single crystals of the same nature at different growth stages, but they may also be intergrown. In the dark-field images of cubes, thickness contours are clearly seen (Fig. 7 b), while the images of bars exhibit steps at facets (Fig. 7 c). Composite hydrogel No. 9, synthesized at lower acrylamide concentration c AAm =0.5 M and c Au =3 mM, contained the same large spheroidal faceted polycrystals, as well as smaller crystals ~ 50 nm in size, shaped like hexagonal pyramids some of which were coalesced along the narrow interblock boundary (Fig. 8 ). 3.6 Thermal analysis By the example of products No. 8 and 9, the decomposition of composite hydrogels proceeded in 4 steps (Table 3 , Fig. 9 ). The first two steps that proceeded up to ~ 337° (No. 8)/339°C (No. 9) were accompanied by insignificant endo-effects and were related to the removal of volatile components from the composite. At the third step, up to ~ 442°/421°C, decomposition (destruction) of the organic matrix proceeded, and exo-effect was observed. The fourth step, up to ~ 667°/802°C, proceeded with a substantial exothermal effect with the maximum at 577°/510°C and corresponded to the complete combustion of carbon-containing products formed at previous steps of decomposition. No mass changes were observed during subsequent heating to 1200°C. Since gold content in the products did not exceed ~ 0.06% as provided by synthesis conditions, the complete mass loss during heating was in fact 100%. Table 3 Results of thermal analysis of products No. 8 and No. 9 Product Decomposition step Temperature range, °C Mass loss, % Т DTG , °C Т DSC , °C No. 8 I 30–205 7 174 II 205–337 21 274 III 337–442 22 388 IV 442–667 50 590 577 No. 9 I 30–213 7 135 II 213–339 21 273 III 339–421 14 390 IV 421–802 58 540 510 Note : a portion of 10.4 mg (No. 8) and 2.52 mg (No. 9); Т DTG – temperature corresponding to the maximal mass loss rate at decomposition step; Т DSC – temperature at which the maximal thermal effect of decomposition is achieved 3.7 Plasmon films The films were obtained using composite hydrogel No. 8. The spectra of the film at deposition cycles 1–8 are shown in Fig. 10 along with growth dependences showing the changes of film extinction at specific wavelengths ( A λ ) depending on the number of cycles (n) – at the maximum of SPR band of nanoparticles, as well as to the left and to the right of the maximum. The intensity of spectrum increased with an increase in film thickness. Judging from the linearity of growth dependences A λ = a + b ·n, where a and b are parameters, an increment per one cycle was approximately the same in the described experiments. Tests of the effect of substrate rotation rate on film formation showed that an increase in ω above ~ 1000 rpm was unreasonable because it caused a substantial decrease in extinction increment (Fig. 11 ), which means also a decrease in film thickness at formation cycle because of the removal of substantial gel portion from the substrate under the action of centrifugal force. The transition from hydrogels to the films of dry composite containing Au NPs and PAAm and then to thin films composed of gold alone implied the necessity of thermal treatment of the samples. The spectra of composite hydrogel and its film after drying at 100°C, as well as after organic mass burning at 550°C, are compared in Fig. 12 . Initial hydrogel had a spectrum with the parameters of SPR band maximum λ max = 556 nm and A max =0.076. After drying, the distances between Au NPs distributed in PAAm matrix decreased, while the interaction between them increased, so that, in qualitative agreement with the theory [ 29 , 30 ], the position of SPR band shifted to longer wavelengths by 30 nm to λ max = 586 nm, while the intensity was conserved: A max =0.076. Further burning of the matrix at high temperature seemed not to change Au NPs arrangement on substrate surface, as band position remained almost the same: λ max = 583 nm, though extinction at the maximum slightly decreased ( A max =0.072) because of slight band broadening. Thin Au film obtained after thermal treatment possessed high optical homogeneity. This was confirmed by the spectra of the film recorded at different sample rotation angles in the plane perpendicular to the light beam direction in the spectrophotometer (Fig. 12 ). Since the beam has the shape of a projection of a narrow slit of the spectrophotometer onto the sample plane, rotation of the sample in a plane perpendicular to the beam leads to the beam hitting and measuring the spectrum in different parts of the film. Digital photographs of three films I-III after different kinds of thermal treatment are shown in Fig. 13 a-c. The films were prepared from the same hydrogel ( с Au =3 mM, с AAm =1 M) but had different thickness and therefore different extinction values. Immediately after formation and drying in the air at 100°C, extinction values at the maximum of individual SPR band of films were A max =0.085 (I, λ max = 584 nm), 0.365 (II, 589 nm) and 0.076 (III, 586 nm). Then film III was heated at first at 380°C, and then at 550°C. Visually, the films looked thin and transparent, lilac (I, II) or pinkish (III) in color on a light background and brown on a dark background. The lines drawn on a white sheet below the films are well seen (Fig. 13 a), so is the texture of a black support (Fig. 13 b). The appearance of sample III* provided evidence that partial destruction of the organic matrix and its tarring took place after heating at 380°C (Fig. 13 c). It is seen at a 10-fold magnification in the photograph of sample III after complete matrix burnoff that the film was composed of uniform granules (Fig. 13 d). In addition, periodic waviness is seen, which may be due to sample rotation during film deposition using the spin-coating method. The SEM images of Au NPs in the dried film I were blurred because of the polymeric matrix (Fig. 14 a). One can see in sharper images of annealed sample III that the film was composed of rounded particles up to ~ 200 nm in diameter, distributed uniformly over the surface. Evaluation of the number of particles per unit area was ~ 20 µm − 2 =2×10 9 cm − 2 (Fig. 14 b). Taking into account the TEM and X-ray data, it can be assumed that the particles visible in the SEM images were clusters or islands of smaller particles (< 100 nm) that were recorded by TEM and, in turn, consisted of even smaller crystallites (CSR ~ 20 nm). Test experiments have shown that the obtained composite hydrogel may be used to manufacture products by means of casting. Transparent films and plates of Au NPs composite with PAAm can be obtained on smooth surfaces. A result of hydrogel casting in a mould, which was a standard cell, 1 cm in size, made of polystyrene, is shown in Fig. 15 . While water was evaporated from hydrogel in the cell, the gel under drying was dragged to cell walls, and after complete drying the composite followed the shape of cell. Due to the weak adhesion of dry composite to glass and plastics, cast products are well separated from the mould. Filaments can be formed by pressing the composite hydrogel through extrusion nozzles. 4 Conclusions A single-stage synthesis of the hybrid composite of Au NPs with polyacrylamide hydrogel from a mixture of crystal HAuCl 4 ∙ x H 2 O, acrylamide powder, water, and a small amount of (NH 4 ) 2 S 2 O 8 as additive to initiate AAm polymerization has been developed as a result of the studies. After initial reagent mixing to make a homogeneous solution, the synthesis does not require operator’s intervention. Under optimal conditions (initial concentrations: с Au =3 mM, с AAm =1 M, c (NH4)2S2O8 =1.2 mM, temperature: 60°C, heating time: 6 hours) a stable product is obtained, containing polycrystalline Au NPs up to ~ 10 2 nm in size, with a clearly pronounced SPR band with the maximum at λ max = 552 nm. The hybrid composite may be used to obtain the plasmon films of dry Au NPs-PAAm composite or thin Au films after thermal removal of the polymer matrix. The hybrid composite is also suitable for obtaining filaments and products by the mould casting. Hydrogel, solid composite, and products made of it (films, plates, fibers, etc.), in particular after additional targeted chemical modification (functionalization) of Au NPs and/or PAAm matrix, may be of interest as a basis for further studies for plasmon sensorics of substances and media in chemistry and biomedicine. Declarations Acknowledgements We express our gratitude to Ph.D. V.I. Zaikovsky (Boreskov Institute of Catalysis SB RAS) and Ph.D. E.A. Maksimovsky (Nikolaev Institute of Inorganic Chemistry SB RAS) for obtaining TEM and SEM images, respectively. Funding This work was supported by the Russian Foundation for Basic Research (Grant No. 20-03-00017) and the Ministry of Science and Higher Education of the Russian Federation (Grant Nos. 121031700315-2 and 121031700313-8). Author Contributions All authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by Vladimir Tatarchuk (synthesis, UV-visible spectroscopy data), Sergey Gromilov (XRD data) and Pavel Plyusnin (synchronous thermal analysis data). The first draft of the manuscript was written by Vladimir Tatarchuk, and all authors commented on the previous versions of the manuscript. All authors have read and approved the final manuscript. Complliance with ethical standards Conflict of interest The authors declare that they have no competing interests. References Yi C, Yang Y, Liu B, He J, Nie Z (2020) Polymer-guided assembly of inorganic nanoparticles. Chem Soc Rev 49:465-508. https://doi.org/10.1039/c9cs00725c Li Z, Fan Q, Yin Y (2022) Colloidal self-assembly approaches to smart nanostructured materials. Chem Rev 122:4976-5067. https://doi.org/10.1021/acs.chemrev.1c00482 Pastoriza-Santos I, Kinnear C, Pérez-Juste J, Mulvaney P, Liz-Marzán LM (2018) Plasmonic polymer nanocomposites. Nature Rev Mater 3:375-391. https://doi.org/10.1038/s41578-018-0050-7 Li D, He Q, Li J (2009) Smart core-shell nanocomposites: Intelligent polymers modified gold nanoparticles. Adv Coll Inter Sci 149:28-38. https://doi.org/10.1016/j.cis.2008.12.007 Jiang C, Qian Y, Gao Q, Dong J, Qian W (2010) In Situ controllable preparation of gold nanorods in thermo-responsive hydrogels and their application in surface enhanced Raman scattering. J Mater Chem 20:8711–8716. https://doi.org/10.1039/c0jm01582b Zhan C, Moskovits M, Tian Z-Q (2020) Recent progress and prospects in plasmon-mediated chemical reaction. Matter 3:42-56. https://doi.org/10.1016/j.matt.2020.03.019 Guglielmi M, Martucci A (2018) Sol-gel nanocomposites for optical applications. J Sol-Gel Sci Technol 88:551-563. https://doi.org/10.1007/s10971-018-4846-0 Wang C, Liu X, Wulf V, Vázquez-González M, Fadeev M, Willner I (2019) DNA-Based hydrogels loaded with Au nanoparticles or Au nanorods: Thermoresponsive plasmonic matrices for shape-memory, self-healing, controlled release, and mechanical applications. ACS Nano 13:3424-3433. https://doi.org/10.1021/acsnano.8b09470 Kallontzi S, Fabris L, Jitianu M, Hernandez A, Jitianu A, Klein LC (2019) Gold nanoparticles in melting gels. J Sol-Gel Sci Technol 91:189-197. https://doi.org/10.1007/s10971-019-04997-2 Wang P, Zhang L, Xia Y, Tong L, Xu X, Ying Y (2012) Polymer nanofibers embedded with aligned gold nanorods: A new platform for plasmonic studies and optical sensing. Nano Lett 12:31453150. https://doi.org/10.1021/nl301055f Pardo-Yissar V, Gabai R, Shipway AN, Bourenko T, Willner I (2001) Gold nanoparticle-hydrogel composites with solvent-switchable electronic properties. Adv Mater 13:1320-1323. https://doi.org/10.1002/1521-4095(200109)13:173.0.CO;2-8 Yata T, Takahashi Y, Tan M, Nakatsuji H, Ohtsuki S, Murakami T, Imahori H, Umeki Y, Shiomi T, Takakura Y, Nishikawa M (2017) DNA nanotechnology-based composite-type gold nanoparticle immunostimulatory DNA hydrogel for tumor photothermal immunotherapy. Biomaterials 146:136-145. https://doi.org/10.1016/j.biomaterials.2017.09.014 Correa S, Grosskopf AK, Lopez Hernandez H, Chan D, Yu AC, Stapleton LM, Appel EA (2021) Translational Applications of Hydrogels. Chem Rev 121:11385-11457. https://doi.org/10.1021/acs.chemrev.0c01177 Pan L, Yu G, Zhai D, Lee HR, Zhao W, Liu N, Wang H, Tee BC-K, Shi Y, Cui Y, Bao Z (2012) Hierarchical nanostructured conducting polymer hydrogel with high electrochemical activity. PNAS 109:9287-9292. https://doi.org/10.1073/pnas.1202636109 Ding F, Ding H, Shen Z, Qian L, Ouyang J, Zeng S, Seery TAP, Li J, Wu G, Chavez SE, Smith AT, Liu L, Li Y, Sun L (2021) Super stretchable and compressible hydrogels inspired by hook-and-loop fasteners. Langmuir 37:7760-7770. https://doi.org/10.1021/acs.langmuir.1c00924 Lu C-H, Qi X-J, Orbach R, Yang H-H, Mironi-Harpaz I, Seliktar D, Willner I (2013) Switchable catalytic acrylamide hydrogels cross-linked by hemin-G-quadruplexes. Nano Lett 13:1298-1302. https://doi.org/10.1021/nl400078g Liu X, Zhang J, Fadeev M, Li Z, Wulf V, Tian H, Willner I (2019) Chemical and photochemical DNA “gears” reversibly control stiffness, shape-memory, self-healing and controlled release properties of polyacrylamide hydrogels Chem Sci 10:1008-1016. https://doi.org/10.1039/c8sc04292f Zhao D, Zhu Y, Cheng W, Xu G, Wang Q, Liu S, Li J, Chen C, Yu H, Hu L (2020) A dynamic gel with reversible and tunable topological networks and performances. Matter 2:390-403. https://doi.org/10.1016/j.matt.2019.10.020 Xiao Y, Wang C, Liu K, Wei L, Luo Z, Zeng M, Yi Y (2021) Promising pure gold aerogel: in situ preparation by composite sol–gel and application in catalytic removal of pollutants and SERS. J Sol-Gel Sci Technol 99:614-626. https://doi.org/10.1007/s10971-021-05597-9 Wang F, Huang Q, Su H, Cui H (2023) Self-assembling paclitaxel-mediated stimulation of tumor-associated macrophages for postoperative treatment of glioblastoma. PNAS 120:e2204621120. https://doi.org/10.1073/pnas.2204621120 Heo YJ, Shibata H, Okitsu T, Kawanishi T, Takeuchi S (2011) Long-term in vivo glucose monitoring using fluorescent hydrogel fibers. PNAS 108:13399-13403. https://doi.org/10.1073/pnas.1104954108 Ward MA, Georgiou TK (2011) Thermoresponsive polymers for biomedical applications. Polymers 3:1215-1242. https://doi.org/10.3390/polym3031215 Di Benedetto F, Biasco A, Pisignano D, Cingolani R (2005) Patterning polyacrylamide hydrogels by soft lithography. Nanotechnology 16:S165-S170. https://doi.org/10.1088/0957-4484/16/5/006 Brauer G (ed) Handbook of Preparative Inorganic Chemistry (1965) New York, Acad. Press Prescher C, Prakapenka VB (2015) DIOPTAS: a program for reduction of two-dimensional X-ray diffraction data and data exploration. High Pressure Research 35:223-230. https://doi.org/10.1080/08957959.2015.1059835 Kraus W, Nolze G (1996) POWDER CELL – a program for the representation and manipulation of crystal structures and calculation of the resulting X-ray powder patterns. J Appl Crystallogr 29:301-303. https://doi.org/10.1107/S0021889895014920 Tatarchuk VV, Dobrolubova YO, Druzhinina IA, Zaikovskii VI, Gevko PN, Maksimovskii EA, Gromilov SA (2016) Facile synthesis of gold nanoparticles in aqueous acrylamide solution. Russ J Inorg Chem 61:535-543. https://doi.org/10.1134/S0036023616040203 Tatarchuk V, Druzhinina I, Zaikovskii V, Maksimovskii E, Korolkov I, Antonova O (2018) Synthesis of ZnO nanoparticles and a composite with polyacrylamide in acrylamide solutions. J Sol-Gel Sci Technol 85:66-75. https://doi.org/10.1007/s10971-017-4512-y Jiang C, Markutsya S, Tsukruk VV (2004) Collective and individual plasmon resonances in nanoparticle films obtained by spin-assisted layer-by-layer assembly. Langmuir 20:882-890. https://doi.org/10.1021/la0355085 Storhoff JJ, Lazarides AA, Mucic RC, Mirkin CA, Letsinger RL, Schatz GC (2000) What controls the optical properties of DNA-linked gold nanoparticle assemblies? J Am Chem Soc 122:4640-4650. https://doi.org/10.1021/ja9938251 Additional Declarations No competing interests reported. Supplementary Files floatimage1.jpeg Graphical abstract Cite Share Download PDF Status: Published Journal Publication published 20 Mar, 2024 Read the published version in Journal of Sol-Gel Science and Technology → Version 1 posted Editorial decision: Revision requested 13 Feb, 2024 Reviews received at journal 22 Jan, 2024 Reviewers agreed at journal 22 Jan, 2024 Reviewers invited by journal 20 Jan, 2024 Editor assigned by journal 17 Jan, 2024 Submission checks completed at journal 17 Jan, 2024 First submitted to journal 17 Jan, 2024 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-3871911","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":267563961,"identity":"db81ebe7-e99f-45ce-8b4c-84a1993fb76d","order_by":0,"name":"Vladimir Tatarchuk","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAApklEQVRIiWNgGAWjYHACxgcMBhIkqOdhYGY2IFkLGynqgcCe/fyx6oICC3kG6faHHxj3HCbCFp5kttszDCQMG2TOGEswPCNGCwNQC4+BRAKDRA4bA8MBYrTwP2YrhmhJf0akFolkNmaIlgQzIrXceGwsDdRi2CaRYyyRcCCdsBb2/sSHn3n+1MnzS6Q//PDhgDVhLXDABiISSNAwCkbBKBgFowAPAAAQkCpZ6nk4owAAAABJRU5ErkJggg==","orcid":"","institution":"Nikolaev Institute of Inorganic Chemistry, Siberian Branch of the Russian Academy of Sciences","correspondingAuthor":true,"prefix":"","firstName":"Vladimir","middleName":"","lastName":"Tatarchuk","suffix":""},{"id":267563962,"identity":"747510f8-69bc-4967-aae0-5607ee08ebed","order_by":1,"name":"Sergey Gromilov","email":"","orcid":"","institution":"Nikolaev Institute of Inorganic Chemistry, Siberian Branch of the Russian Academy of Sciences","correspondingAuthor":false,"prefix":"","firstName":"Sergey","middleName":"","lastName":"Gromilov","suffix":""},{"id":267563963,"identity":"177a9a06-88c0-4a51-acb3-c53edf6626fd","order_by":2,"name":"Pavel Plyusnin","email":"","orcid":"","institution":"Nikolaev Institute of Inorganic Chemistry, Siberian Branch of the Russian Academy of Sciences","correspondingAuthor":false,"prefix":"","firstName":"Pavel","middleName":"","lastName":"Plyusnin","suffix":""}],"badges":[],"createdAt":"2024-01-17 05:14:11","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-3871911/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-3871911/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s10971-024-06366-0","type":"published","date":"2024-03-20T15:01:24+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":49829485,"identity":"abf8da73-4e0e-46e7-9780-ef9196fc00c1","added_by":"auto","created_at":"2024-01-18 16:12:23","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":495761,"visible":true,"origin":"","legend":"\u003cp\u003eSpectral manifestation of Au NPs synthesis process: a – evolution of the spectrum of reaction mixture for 6 hours at 60°C (scanning step: 5 min), and the spectrum on the 4th day after heating was complete (dash line); b – spectra in 6 hours after the start of synthesis at 55° (1), 60° (2) and 65°С (3), l=1 cm; c, d – kinetics at 65° (solid line), 60° (dash line) and 55°С (dots) at fixed wavelengths, l=1 cm. cAu=0.26 mM, cAAm=1 M\u0026nbsp;\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-3871911/v1/f0402a735338b9e2e55877b4.png"},{"id":49828577,"identity":"d706f00f-1f0b-48a0-a886-8a0715fb578e","added_by":"auto","created_at":"2024-01-18 16:04:23","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":416537,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of initial acrylamide concentration on synthesis results and product stability: the spectra of composite hydrogels immediately after synthesis at 60°C (dash line) and after storage for 1 month under usual conditions in a closed cell (solid line), cAAm=1 (a), 0.5 (b), 0.26 (c) and 0.1 М (d); cAu=0.26 mM, l=1 cm. Numbers near the spectra indicate the wavelengths of SPR band maxima\u0026nbsp;\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-3871911/v1/8d8fa55d277f07aaa83b3d12.png"},{"id":49828580,"identity":"d99c624f-74bb-426a-965c-5dc5e6ae56b0","added_by":"auto","created_at":"2024-01-18 16:04:23","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":374034,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of initial gold concentration on synthesis results and product stability: the spectra of composite hydrogels immediately after synthesis at 60°C (dash line) and after storage for 4 days under usual conditions in a closed cell (solid line), cAu=10 (a), 3 (b), 1 (c) and 0.26 mM (d); cAAm=1 M, l=0.2 (b) and 1 cm (a, c, d). Numbers near the spectra indicate the wavelengths of SPR band maxima\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-3871911/v1/56b73f5f46f6dbbc4465be8f.png"},{"id":49828578,"identity":"ab66dc54-6bf5-46c1-8758-0c6e1d96b908","added_by":"auto","created_at":"2024-01-18 16:04:23","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":16387,"visible":true,"origin":"","legend":"\u003cp\u003eReproducibility of synthesis under optimal conditions (cAu=3 mM, cAAm=1 M, 60°C): spectra of products obtained in two independent experiments with a time lag of one month, l=0.2 cm\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-3871911/v1/f769936c5ed580079e0d0e58.png"},{"id":49828588,"identity":"ca12e50c-7046-4344-b351-768dd87307f5","added_by":"auto","created_at":"2024-01-18 16:04:23","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":282244,"visible":true,"origin":"","legend":"\u003cp\u003eAn example of diffraction patterns for the gel sample synthesized at cAu=3 mM and cAAm=0.5 M. Debye powder pattern is shown in the insert\u0026nbsp;\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-3871911/v1/c82759142508b4b3b060cec9.png"},{"id":49829489,"identity":"43d57b6d-0c72-491b-80a8-37a1aff46fad","added_by":"auto","created_at":"2024-01-18 16:12:23","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":1073761,"visible":true,"origin":"","legend":"\u003cp\u003eLight- and dark-field TEM images of gold crystals in product No. 1. The size distribution of cross-sections of intergrown crystals is shown in the inset\u0026nbsp;\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-3871911/v1/de8555604de1d5f9f11c06e8.png"},{"id":49828589,"identity":"0a2aec00-57fe-42e5-b0cd-abd9b7456f97","added_by":"auto","created_at":"2024-01-18 16:04:23","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":3194872,"visible":true,"origin":"","legend":"\u003cp\u003eLight- and dark-field TEM images of gold crystals with different morphology (a, b, c) in product No. 8\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-3871911/v1/cc15311781d74a86351dd7e4.png"},{"id":49829491,"identity":"2318b2c0-c866-411a-b96d-872af87f6b67","added_by":"auto","created_at":"2024-01-18 16:12:23","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":2256620,"visible":true,"origin":"","legend":"\u003cp\u003eLight- and dark-field TEM images of a separate gold crystal and two intergrown ones in product No. 9\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-3871911/v1/ee000eafa6feecc39627586e.png"},{"id":49828585,"identity":"678a71ec-b2d3-4a9f-a365-a346b4613eda","added_by":"auto","created_at":"2024-01-18 16:04:23","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":364792,"visible":true,"origin":"","legend":"\u003cp\u003eCurves of thermal analysis for the composite hydrogel No. 8 in the atmosphere of oxygen (20 %) mixture with argon at the heating rate of 10°C/min\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-3871911/v1/260564b8e5c3ba977674a2d1.png"},{"id":49829823,"identity":"ea84993b-5748-456a-a0c6-5c089ea1ceef","added_by":"auto","created_at":"2024-01-18 16:20:23","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":45043,"visible":true,"origin":"","legend":"\u003cp\u003eAn increase in the intensity of film spectrum while 8 deposition cycles are performed (left) and growth dependences at λ=589 (1), 400 (2) and 1000 nm (3) (right). Conditions: gel portion per cycle – 0.1 mL, ω=990 rpm, spinning time per cycle – 15 min\u003c/p\u003e","description":"","filename":"10.png","url":"https://assets-eu.researchsquare.com/files/rs-3871911/v1/d0451922317563741c0ac97a.png"},{"id":49828582,"identity":"9c60555e-d56b-4e4e-ba2a-4456f1ebf522","added_by":"auto","created_at":"2024-01-18 16:04:23","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":11516,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of substrate rotation rate on the increment of film extinction per one deposition cycle\u0026nbsp;\u003c/p\u003e","description":"","filename":"11.png","url":"https://assets-eu.researchsquare.com/files/rs-3871911/v1/0728ba7037f4aff6978f9aa9.png"},{"id":49829824,"identity":"2735a3fc-227a-426b-958f-1da393c610b9","added_by":"auto","created_at":"2024-01-18 16:20:23","extension":"png","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":201383,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of thermal treatment on the spectrum (left) and optical homogeneity of the film (right). 1 – 30-fold down-sized spectrum of the composite hydrogel in 0.2 cm cell, 2 – spectrum of the film dried at 100°C, 3 – spectrum of the film heated at 550°C, 4 and 5 – boundary lines of the range of heated film variation spectrum for its rotation by 0°, 90°, 180° and 270° in the plane perpendicular to the light beam in the spectrophotometer\u0026nbsp;\u003c/p\u003e","description":"","filename":"12.png","url":"https://assets-eu.researchsquare.com/files/rs-3871911/v1/0a02b375f2dac9111ce4ce1d.png"},{"id":49828591,"identity":"1b234a27-ab3e-4cfc-8db9-a762c531893e","added_by":"auto","created_at":"2024-01-18 16:04:23","extension":"png","order_by":13,"title":"Figure 13","display":"","copyAsset":false,"role":"figure","size":3744357,"visible":true,"origin":"","legend":"\u003cp\u003eDigital photographs of films I–II dried at 100°C, and film III heated at 550°C, against the light (a) and dark background (b), as well as film III, heated at 380°C (c), and the surface of film III heated at 550°C and illuminated with a red laser, at a ×10 magnification (c)\u0026nbsp;\u003c/p\u003e","description":"","filename":"13.png","url":"https://assets-eu.researchsquare.com/files/rs-3871911/v1/abd100c4a238c999f5043d3c.png"},{"id":49828592,"identity":"847a7a13-01e0-403d-9cd7-7d103ae6dc75","added_by":"auto","created_at":"2024-01-18 16:04:23","extension":"png","order_by":14,"title":"Figure 14","display":"","copyAsset":false,"role":"figure","size":1742929,"visible":true,"origin":"","legend":"\u003cp\u003eSEM images of film I dried at 100°C (a) and film III heated at 550°C (b) at different magnifications\u0026nbsp;\u003c/p\u003e","description":"","filename":"14.png","url":"https://assets-eu.researchsquare.com/files/rs-3871911/v1/f110e09e5a1ff2a4dcb420a5.png"},{"id":49829487,"identity":"5f50c626-1a4a-42b4-a42b-339d58c2273f","added_by":"auto","created_at":"2024-01-18 16:12:23","extension":"png","order_by":15,"title":"Figure 15","display":"","copyAsset":false,"role":"figure","size":783616,"visible":true,"origin":"","legend":"\u003cp\u003eProduct obtained by pouring a composite hydrogel into a polystyrene cell and then spontaneously drying in air at room temperature, top view (left) and bottom view (right)\u003c/p\u003e","description":"","filename":"15.png","url":"https://assets-eu.researchsquare.com/files/rs-3871911/v1/4f331959907e3228438c9b0b.png"},{"id":53403710,"identity":"e2f43d17-7f22-452b-a03d-c12fd78a2714","added_by":"auto","created_at":"2024-03-25 15:13:59","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":7957394,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-3871911/v1/aee6c8db-6a48-4e12-b22e-86e41793c4aa.pdf"},{"id":49829486,"identity":"041a9761-eb24-41d5-bb0e-8991934e055e","added_by":"auto","created_at":"2024-01-18 16:12:23","extension":"jpeg","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":67783,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eGraphical abstract\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"floatimage1.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-3871911/v1/d292098c38d30d8224ef8347.jpeg"}],"financialInterests":"No competing interests reported.","formattedTitle":"Hybrid composite of gold nanoparticles with polyacrylamide hydrogel: one-step synthesis, preparation of plasmon films, characterization","fulltext":[{"header":"Highlights","content":"\u003cul\u003e\n \u003cli\u003eA hybrid composite of gold nanoparticles with polyacrylamide hydrogel was synthesized by a one-pot, one-step method from H[AuCl\u003csub\u003e4\u003c/sub\u003e] and acrylamide\u0026nbsp;\u003c/li\u003e\n \u003cli\u003eOptimal conditions for the synthesis of a stable product are initial concentrations of 3 mM for gold and 1 M for acrylamide, temperature 60\u0026deg;C\u0026nbsp;\u003c/li\u003e\n \u003cli\u003eUsing a composite hydrogel on glass, films of a dry composite of gold nanoparticles with polyacrylamide were obtained by dehydration at 100\u0026deg;C and thin gold after heating at 550\u0026deg;C\u0026nbsp;\u003c/li\u003e\n \u003cli\u003eSurface plasmon resonance bands in the spectra of the synthesized hybrid composite hydrogel and of films have favorable for use in optical sensing well-defined maxima in the wavelength range 570-600 nm\u0026nbsp;\u003c/li\u003e\n\u003c/ul\u003e"},{"header":"1 Introduction","content":"\u003cp\u003eNanoparticles (NPs) are of great importance for modern science and technology. Nor sole NPs but their ensembles are significant for their practical use [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e], either in liquid media (solvents or solutions), in solid matrices (polymers, glasses, ceramics), or in the form of 1\u0026ndash;2D-structures in fibers and on surfaces (layers, films). Combinations of NPs with matrices form nanocomposites, which are hybrid if the matrices are based on organic or biological polymers. Hybrid nanocomposites composed of plasmon metal NPs of Au (or Ag), distributed in semi-solid (soft) matrices of polymer hydrogels attract special attention [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Unlike composites with solid matrices possessing fixed static properties, hybrid gel composites open the way to dynamic materials allowing controllable changes of properties and responses to various external chemical, physical or mechanical actions (stimuli) [\u003cspan additionalcitationids=\"CR4\" citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. These composite materials not only combine the properties of structured NPs ensembles and matrices but also gain some new functions [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eDue to the local surface plasmon resonance (SPR) arising in nanometer-sized metal particles under the action of light, Au NPs are able to absorb, concentrate, scatter, redistribute and transform (convert) photon energy [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan additionalcitationids=\"CR7\" citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. In this respect, Au NPs in hybrid composites may act as optical sensors (probes) for reagents and media [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan additionalcitationids=\"CR8 CR9\" citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e], substrates for SERS [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e], contrast agents for visualization of nano- and micrometer-sized objects [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e], optical filters [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e], as photocatalytic and photothermal triggers of physicochemical and mechanical processes at the micro level [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. In addition, they may serve as light guides due to plasmon interactions [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e], and render electrical conduction to materials due to the metal nature of the cores [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. It is essential that gold is not toxic, biocompatible [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e] and possesses high affinity to DNA [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eIn turn, polymer hydrogels, which are polymer networks cross-linked through covalent bridges or/and labile bonds (hydrogen, molecular) and are able to absorb and retain water reversibly in the amount up to 99% of the mass of hydrogel [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e], act in hybrid composites as a matrix medium providing dispersity and stability of the structured NPs ensemble [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. In addition, they may, in particular after additional modifications, function as smart materials that respond to the action of various stimuli (light, temperature, solvent, pH, chemical reagents, physical deformation) reversibly changing their volume and structure, switching gel/solution or gel/solid states, and self-restoring [\u003cspan additionalcitationids=\"CR16 CR17\" citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eHydrogels described in publications are based on polyaniline [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e], cellulose [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e], DNA [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e], polyanhydride (polifeprosan 20) [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e], organosilicon polymers [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. Many studies deal with the hydrogels based on the derivatives of polyacrylamide (PAAm) [\u003cspan additionalcitationids=\"CR16\" citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e, \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e] and their composites with Au NPs [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. High hydration degree and three-dimensional network-type structure render polymer hydrogels similarity and compatibility with biological tissues of living organisms [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e], and Au NPs are also biocompatible, as mentioned above, so the application potential of hybrid Au NPs composites with the hydrogels of PAAm and its derivatives is first of all directed towards medicine. Possible application areas include theranostics, photoacoustic visualization, and photothermal therapy [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e], drug transport, molecular recognition, chemical valves and chemical-mechanical energy transformation, artificial tissues/muscles [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e], compact sensitive sensor devices [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e], controllable photoinduced drug release [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eIt should also be stressed that polyacrylamide hydrogel is well suitable for developing microstructures with high spatial resolution using already refined methods, for example soft lithography [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e], which is essential for the application of composite gels in working devices.\u003c/p\u003e \u003cp\u003eFour approaches to obtaining hybrid polymeric nanocomposites are known: 1) the formation of a polymeric matrix in NPs suspension, 2) inclusion of NPs into preliminarily formed polymer matrix, 3) \u003cem\u003ein situ\u003c/em\u003e synthesis of NPs in the preliminarily formed polymer, and 4) the formation of polymeric matrix promoted by functionalized NPs [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. With all these approaches, the synthesis is relatively complex and multi-step. In our work, we tested the approach based on the simultaneous synthesis of Au NPs and PAAm from a mixture of precursors, which are HAuCl\u003csub\u003e4\u003c/sub\u003e and acrylamide (AAm).\u003c/p\u003e \u003cp\u003eThe objectives of our investigation were: 1) to test the possibility of the single-stage synthesis of a hybrid composite of Au NPs with PAAm hydrogel through HAuCl\u003csub\u003e4\u003c/sub\u003e reduction with acrylamide and simultaneous radical polymerization of AAm, initiated by ammonium persulfate, in the aqueous solution; 2) to optimize the conditions for obtaining phase-stable product, with respect to the initial concentrations of Au and AAm; 3) to study the effect of concentration-related synthesis conditions on the morphology and structure of Au NPs; 4) to obtain the plasmon films from the solid composite of Au NPs/PAAm and after thermal removal of the polymer matrix, and to characterize these films.\u003c/p\u003e"},{"header":"2 Experimental","content":"\u003cp\u003eThe chemicals used in the work were HAuCl\u003csub\u003e4\u003c/sub\u003e\u0026middot;\u003cem\u003ex\u003c/em\u003eH\u003csub\u003e2\u003c/sub\u003eO preparation obtained from metal gold (wire) according to a generally accepted procedure [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e] and the following reagents: acrylamide for electrophoresis (\u0026gt;\u0026thinsp;99.0%, specially pure reagent grade, Medigen), ammonium persulfate (98%, reagent grade, Sigma-Aldrich).\u003c/p\u003e \u003cp\u003eTo synthesize a hybrid composite of Au NPs with PAAm hydrogel, weighed portions of crystal HAuCl\u003csub\u003e4\u003c/sub\u003e∙\u003cem\u003ex\u003c/em\u003eH\u003csub\u003e2\u003c/sub\u003eO and AAm powder, placed in one vessel, were poured with an aqueous solution of 1.2 mM (NH\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e8\u003c/sub\u003e, heated to the desired temperature (55\u0026deg;, 60\u0026deg;, or 65\u0026deg;C), which was the initiator of radical polymerization of AAm. The mixture was stirred until the solid components dissolved. The reaction mixture was kept in a closed vessel for 6 hours in a drying box at the selected temperature. In kinetic experiments, the mixture was pored into a thermostated spectrophotometric cell to record the changes in the UV-vis spectrum during the synthesis.\u003c/p\u003e \u003cp\u003eThe substrates for making the films were square, 25\u0026times;25\u0026times;1 mm in size, cut from microscopic slides (Heinz Herenz, Germany). Substrate preparation included the treatment in an ultrasonic bath for 10 min in the 2% aqueous solution of Fairy detergent, washing with distilled water, exposure in a mixture of concentrated H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e and H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e (3:1), washing with deionized water, drying in the air in the drying box at 100\u0026deg;C. The films were deposited by spin-coating. The deposition cycle proceeded as follows: a portion of the gel was dropped into the center of the substrate, spinning was turned on and continued at the fixed spin rate (ω) for the necessary time interval (\u003cem\u003et\u003c/em\u003e, relatively long because of the high viscosity of the gel), and dried in the air at 100\u0026deg;C. To form the film, the deposition cycle was repeated as many times as necessary (n). Drying caused the formation of a solid composite film of Au NPs and PAAm, while subsequent heating at 550\u0026deg;C resulted in the formation of an isle-type thin gold film.\u003c/p\u003e \u003cp\u003eThe UV-vis spectra of solutions were recorded with respect to water, and films with respect to pure substrates, with the help of Shimadzu UV-1700 spectrophotometer.\u003c/p\u003e \u003cp\u003eThe average hydrodynamic diameter of the polymer globules of PAAm in hydrogels (\u003cem\u003ed\u003c/em\u003e\u003csub\u003ePAAm\u003c/sub\u003e) was measured by means of photon-correlation spectroscopy at an angle of 90\u0026deg; in the quartz cell with the section of 1\u0026times;1 cm at room temperature using a 90Plus spectrometer (Brookhaven Inst). Averaging was carried out over the number of particles within the hypothesis of lognormal distribution.\u003c/p\u003e \u003cp\u003eX-ray diffraction investigation of Au NPs in hydrogels and in dried products was carried out using an X-ray diffractometer Bruker D8 Venture (microfocus tube Incoatec 1\u0026micro;S 3.0 Cu, detector PHOTON 3, resolution 768\u0026times;1024, \u003cem\u003eD\u003c/em\u003e\u0026thinsp;=\u0026thinsp;60 mm, 2θ\u003csub\u003eD\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;\u0026minus;\u0026thinsp;40\u0026deg;). The samples were prepared as follows. A drop of hydrogel with Au NPs was deposited onto a slide, and a piece with linear size\u0026thinsp;~\u0026thinsp;0.3 mm was cut off the surface after drying. For sample No. 2, Si powder (SRM 640a, \u003cem\u003ea\u003c/em\u003e\u0026thinsp;=\u0026thinsp;5.430593 \u0026Aring;) was added into the gel to be used further on as an internal standard. The samples were fixed on the goniometer head, centered, and examination was carried out using Debye-Scherrer scheme. The Debye-Scherrer powder patterns were recorded in the mode with the sample completing the turn around the axis φ for 10\u0026ndash;30 min. The introduction of corrections for the reference and the transition to the standard form I(2θ) were performed using the DIOPTAS software [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. To determine the size of coherent scattering regions (CSR) with the POWDER CELL software [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e], the full-profile refinement was carried out (using pseudo-Voigt function) within the angle range from 42.8\u0026deg; to 46.0\u0026deg;2θ, where the (200)\u003csub\u003eAu\u003c/sub\u003e reflection was located. Broadening (Δ) of this reflection was calculated with respect to (220)\u003csub\u003eSi\u003c/sub\u003e (FWHM\u0026thinsp;=\u0026thinsp;0.332\u0026deg;2θ).\u003c/p\u003e \u003cp\u003eSynchronous thermal analysis (STA) was performed using an STA 449F1 Jupiter\u0026reg; instrument (Germany) within the temperature range 30\u0026deg;-1200\u0026deg;C in the atmosphere of synthetic air at the gas flow rate of argon 40 mL/min and oxygen 10 mL/min with the heating rate of 10\u003csup\u003eo\u003c/sup\u003eC/min. Closed crucibles made of Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e were used. The reference sample was an empty crucible with a cap. Experimental data were treated using the Proteus analysis software package.\u003c/p\u003e"},{"header":"3 Results and discussion","content":"\u003cdiv id=\"Sec4\"\u003e\n \u003ch2\u003e3.1 Synthesis of the hybrid composite\u003c/h2\u003e\n \u003cp\u003eThe composite of Au NPs with PAAm hydrogel was obtained by conducting two parallel processes simultaneously in the aqueous solution: synthesis of gold NPs through the reduction of [AuCl\u003csub\u003e4\u003c/sub\u003e]\u003csup\u003e\u0026ndash;\u003c/sup\u003e by the olefin fragment of AAm, and the radical polymerization of AAm. The possibility of these processes to take place was separately determined previously [\u003cspan\u003e27\u003c/span\u003e, \u003cspan\u003e28\u003c/span\u003e].\u003c/p\u003e\n \u003cp\u003eThe UV spectroscopic investigation within the range of 300\u0026ndash;1000 nm allowed us to observe the formation of Au NPs, while other components did not absorb the light at wavelengths longer than 350 nm. The appearance and enhancement of extinction (light absorption\u0026thinsp;+\u0026thinsp;scattering) in the region of ~\u0026thinsp;550 and \u0026gt;\u0026thinsp;650 nm was due to the bands associated with individual and collective SPR of the growing Au NPs (Fig.\u0026nbsp;\u003cspan\u003e1\u003c/span\u003ea). Particle formation was not fast, and it continued after 6-hours long heating stopped, which was confirmed by the spectrum recorded 4 days later. The same was confirmed by the spectra of synthesis products, recorded after heating for 6 hours at different temperatures (Fig.\u0026nbsp;\u003cspan\u003e1\u003c/span\u003eb), and by the behavior of kinetic curves at fixed wavelengths (Fig.\u0026nbsp;\u003cspan\u003e1\u003c/span\u003ec,d). The higher was temperature, the higher was the intensity of spectrum, and therefore the process extent. Kinetic curves at the wavelength of 775 nm in the region of collective SPR exhibited the induction period because the interaction between particles and the collective resonance caused by this interaction emerged not immediately but while the particles were accumulated and grew. Table\u0026nbsp;\u003cspan\u003e1\u003c/span\u003e presents the conditions under which the samples of composite hydrogels were obtained for the purpose of revealing the effect of initial concentrations of gold and acrylamide. Not all these products were homogeneous hydrogels; depending on \u003cem\u003eс\u003c/em\u003e\u003csub\u003eAAm\u003c/sub\u003e and \u003cem\u003eс\u003c/em\u003e\u003csub\u003eAu\u003c/sub\u003e, some samples exhibited insufficient phase stability, and Au NPs were partially or almost completely separated in the form of precipitate.\u003c/p\u003e\n \u003cdiv\u003e\n \u003ctable id=\"Tab1\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv\u003eTable 1\u003c/div\u003e\n \u003cdiv\u003e\n \u003cp\u003eThe studied samples of composite hydrogels: No., obtaining conditions (\u003cem\u003ec\u003c/em\u003e\u003csub\u003e(NH4)2S2O8\u003c/sub\u003e=1.2 mM, 60\u0026deg;C), the presence of precipitates\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003ccolgroup cols=\"4\"\u003e\u003c/colgroup\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eNo.\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eс\u003c/em\u003e\u003csub\u003eAu\u003c/sub\u003e, mM\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eс\u003c/em\u003e\u003csub\u003eAAm\u003c/sub\u003e, M\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003ePrecipitate\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.26\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026ndash;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.26\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026ndash;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.26\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.26\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e+\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.26\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e+\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e+\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026ndash;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026ndash;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026ndash;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e+\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec5\"\u003e\n \u003ch2\u003e3.2 Effect of acrylamide concentration\u003c/h2\u003e\n \u003cp\u003eWith an increase in initial AAm concentration, we observed an increase in the viscosity of the formed polymer hydrogels and the average hydrodynamic diameter of PAAm globules \u0026ndash; \u003cem\u003ed\u003c/em\u003e\u003csub\u003ePAAm\u003c/sub\u003e= 49\u0026thinsp;\u0026plusmn;\u0026thinsp;6 nm (\u003cem\u003eс\u003c/em\u003e\u003csub\u003eAAm\u003c/sub\u003e=0.25 M), 94\u0026thinsp;\u0026plusmn;\u0026thinsp;13 nm (0.5 M), and 158\u0026thinsp;\u0026plusmn;\u0026thinsp;32 nm (1 M). With the fixed gold concentration \u003cem\u003eс\u003c/em\u003e\u003csub\u003eAu\u003c/sub\u003e=0.26 mM, homogeneous and storage-stable for 1 month were the products for acrylamide concentration \u003cem\u003eс\u003c/em\u003e\u003csub\u003eAAm\u003c/sub\u003e=1 and 0.5 M, while for \u003cem\u003eс\u003c/em\u003e\u003csub\u003eAAm\u003c/sub\u003e=0.26 and 0.1 M the precipitate of Au NPs was present (Table\u0026nbsp;\u003cspan\u003e1\u003c/span\u003e). Comparison of the spectra of products immediately after the synthesis during heating and a month later, after storage under usual conditions (Fig.\u0026nbsp;\u003cspan\u003e2\u003c/span\u003e), allows us to assume the following. The stability of products in the case of high \u003cem\u003eс\u003c/em\u003e\u003csub\u003eAAm\u003c/sub\u003e concentrations may be explained by higher acrylamide polymerization rate with respect to the rate of Au NP formation, as well as by the higher viscosity of gel matrix with NPs. The gel medium affected also the rate of Au NPs formation: in the medium with higher viscosity, for \u003cem\u003eс\u003c/em\u003e\u003csub\u003eAAm\u003c/sub\u003e=1 M, the intensity of spectrum related to the synthesis product was initially lower (therefore, the extent of NPs formation was lower) than the intensity of product spectrum at \u003cem\u003eс\u003c/em\u003e\u003csub\u003eAAm\u003c/sub\u003e=0.5 M, other synthesis conditions being equal (Fig.\u0026nbsp;\u003cspan\u003e2\u003c/span\u003ea,b). A month later, the intensities of the spectra approached each other due to complete recovery and [AuCl\u003csub\u003e4\u003c/sub\u003e]\u003csup\u003e\u0026ndash;\u003c/sup\u003e transformation into Au NPs. In this situation, the intensity of individual SPR band of the particles at ~\u0026thinsp;540 nm was higher for the product with the matrix possessing higher viscosity, while the intensity of the band of collective SPR within the range of ~\u0026thinsp;760\u0026ndash;780 nm was higher for the product with less viscous matrix. In the case of low acrylamide concentration \u003cem\u003eс\u003c/em\u003e\u003csub\u003eAAm\u003c/sub\u003e, the intensity of spectra was initially low, especially for \u003cem\u003eс\u003c/em\u003e\u003csub\u003eAAm\u003c/sub\u003e=0.1 M (Fig.\u0026nbsp;\u003cspan\u003e2\u003c/span\u003ec,d), and a month later it dropped almost to zero because of Au NPs sedimentation.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec6\"\u003e\n \u003ch2\u003e3.3 Effect of gold concentration\u003c/h2\u003e\n \u003cp\u003eThe effect of gold concentration at the constant acrylamide concentration \u003cem\u003eс\u003c/em\u003e\u003csub\u003eAAm\u003c/sub\u003e=1 M is illustrated by product spectra presented in Fig.\u0026nbsp;\u003cspan\u003e3\u003c/span\u003e. The best result was obtained for \u003cem\u003eс\u003c/em\u003e\u003csub\u003eAu\u003c/sub\u003e=3 mM (Fig.\u0026nbsp;\u003cspan\u003e3\u003c/span\u003eb): the product was stable, its spectrum reached its maximal limiting intensity during heating at 60\u0026deg;С for 6 hours, remained unchanged further on, and contained a clearly pronounced SPR band related to individual NPs. At \u003cem\u003eс\u003c/em\u003e\u003csub\u003eAu\u003c/sub\u003e=10 and 1 mM, NPs coagulation and precipitation occurred, almost complete in the case of 10 mM Au (Fig.\u0026nbsp;\u003cspan\u003e3\u003c/span\u003ea,c). At \u003cem\u003eс\u003c/em\u003e\u003csub\u003eAu\u003c/sub\u003e=0.26 mM, the process of Au NPs formation continued for a long time after 6-hour long heating was finished (Fig.\u0026nbsp;\u003cspan\u003e3\u003c/span\u003ed).\u003c/p\u003e\n \u003cp\u003eSo, the following conditions were chosen as optimal for the synthesis of stable hybrid composite of Au NPs with PAAm hydrogel: \u003cem\u003eс\u003c/em\u003e\u003csub\u003eAu\u003c/sub\u003e=3 mM, \u003cem\u003eс\u003c/em\u003e\u003csub\u003eAAm\u003c/sub\u003e=1 M, \u003cem\u003ec\u003c/em\u003e\u003csub\u003e(NH4)2S2O8\u003c/sub\u003e=1.2 mM, temperature 60\u0026deg;C, heating time 6 hours. The product obtained under these conditions was a transparent thick gel, violet in transmitted light and brown in reflected light. Synthesis result was steadily reproduced in independent experiments (Fig.\u0026nbsp;\u003cspan\u003e4\u003c/span\u003e).\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec7\"\u003e\n \u003ch2\u003e3.4 X-ray investigation\u003c/h2\u003e\n \u003cp\u003eInvestigation of the products presented in Tables\u0026nbsp;\u003cspan\u003e1\u003c/span\u003e and \u003cspan\u003e2\u003c/span\u003e revealed the presence of gold as the only crystal phase (Fig.\u0026nbsp;\u003cspan\u003e5\u003c/span\u003e). Sample No. 1 of composite hydrogel, synthesized at \u003cem\u003eс\u003c/em\u003e\u003csub\u003eAu\u003c/sub\u003e=0.26 mM and \u003cem\u003eс\u003c/em\u003e\u003csub\u003eAAm\u003c/sub\u003e=1 M, turned out to be X-ray amorphous, in other cases the size of CSR was estimated for Au NPs. The obtained values, along with the positions of maxima and the full width at half-maximum (FWHM), are shown in Table\u0026nbsp;\u003cspan\u003e2\u003c/span\u003e. Under the optimal synthesis conditions (\u003cem\u003eс\u003c/em\u003e\u003csub\u003eAu\u003c/sub\u003e=3 mM, \u003cem\u003eс\u003c/em\u003e\u003csub\u003eAAm\u003c/sub\u003e=1 M), CSR size for gold in NPs was 20\u0026ndash;22 nm (samples Nos. 6 and 8). A decrease in \u003cem\u003eс\u003c/em\u003e\u003csub\u003eAAm\u003c/sub\u003e from 1 to 0.1 M at the fixed low gold concentration \u003cem\u003eс\u003c/em\u003e\u003csub\u003eAu\u003c/sub\u003e=0.26 mM caused an increase in CSR size: No. 1 \u0026ndash; amorphous, No. 4\u0026ndash;18 nm. For higher gold concentration (\u003cem\u003eс\u003c/em\u003e\u003csub\u003eAu\u003c/sub\u003e=3 mM), a decrease in \u003cem\u003eс\u003c/em\u003e\u003csub\u003eAAm\u003c/sub\u003e from 1 to 0.5 M caused a slight increase in CSR size from 20 (No. 8) to 23 (No. 9). For the fixed acrylamide concentration \u003cem\u003eс\u003c/em\u003e\u003csub\u003eAAm\u003c/sub\u003e=1 M, an increase in gold concentration \u003cem\u003eс\u003c/em\u003e\u003csub\u003eAu\u003c/sub\u003e from 0.26 to 3 and then to 10 mM caused a substantial increase in CSR size up to 87 nm (No. 5). At constant \u003cem\u003eс\u003c/em\u003e\u003csub\u003eAAm\u003c/sub\u003e=0.5 M, an increase in \u003cem\u003eс\u003c/em\u003e\u003csub\u003eAu\u003c/sub\u003e from 0.26 to 3 mM caused an increase in CSR size from 10 (No. 2) to 23 nm (No. 9).\u003c/p\u003e\n \u003cdiv\u003e\n \u003ctable id=\"Tab2\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv\u003eTable 2\u003c/div\u003e\n \u003cdiv\u003e\n \u003cp\u003eResults of the treatment of (200)\u003csub\u003eAu\u003c/sub\u003e reflection profile in the diffraction patterns of gel and precipitate samples\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003ccolgroup cols=\"5\"\u003e\u003c/colgroup\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eNo.\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e2\u0026theta; (200), \u0026deg;\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eFWHM (200), \u0026deg;\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u0026Delta; \u003csup\u003ea\u003c/sup\u003e, \u0026deg;\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eCSR, nm\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1 \u003csup\u003eb\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026ndash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026ndash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026ndash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026ndash;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e44.29\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.303\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.971\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e10\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e44.31\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.215\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.883\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e11 \u003csup\u003ec\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e44.29\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.867\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.535\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e18 \u003csup\u003ec\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e44.33\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.442\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.110\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e87 \u003csup\u003ec\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e44.29\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.771\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.439\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e22\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e44,29\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.908\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.576\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e17\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e44.29\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.809\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.477\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e20\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e44.31\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.741\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.409\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e23\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003ctfoot\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"5\"\u003e\u003csup\u003ea\u003c/sup\u003e with respect to the (220)\u003csub\u003eSi\u003c/sub\u003e line (FWHM\u0026thinsp;=\u0026thinsp;0.332\u0026deg;2\u0026theta;); \u003csup\u003eb\u003c/sup\u003e amorphous; \u003csup\u003ec\u003c/sup\u003e for precipitate\u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tfoot\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec8\"\u003e\n \u003ch2\u003e3.5 Transmission electron microscopy\u003c/h2\u003e\n \u003cp\u003eThe TEM images of X-ray amorphous product No. 1 revealed the presence of isometric particles (Fig.\u0026nbsp;\u003cspan\u003e6\u003c/span\u003e), the size of cross sections varies from 21 to 31 nm; the average value is \u003cem\u003ed\u003c/em\u003e\u0026thinsp;=\u0026thinsp;24.5\u0026thinsp;\u0026plusmn;\u0026thinsp;1.2 nm (size distribution is shown in the insert to Fig.\u0026nbsp;\u003cspan\u003e6\u003c/span\u003e). It may be assumed that there is a gel layer between NPs. In the product No. 8, obtained under optimal conditions (\u003cem\u003eс\u003c/em\u003e\u003csub\u003eAu\u003c/sub\u003e=3 mM and \u003cem\u003eс\u003c/em\u003e\u003csub\u003eAAm\u003c/sub\u003e=1 M), NPs of different shapes are observed: spheroids, cubes and bars (Fig.\u0026nbsp;\u003cspan\u003e7\u003c/span\u003e). Spheroid particles (Fig.\u0026nbsp;\u003cspan\u003e7\u003c/span\u003ea) are up to ~\u0026thinsp;102 nm in size and are composed of small crystallites (according to estimations, the size of CSR is 20 nm). Cubes and bars look like single crystals of the same nature at different growth stages, but they may also be intergrown. In the dark-field images of cubes, thickness contours are clearly seen (Fig.\u0026nbsp;\u003cspan\u003e7\u003c/span\u003eb), while the images of bars exhibit steps at facets (Fig.\u0026nbsp;\u003cspan\u003e7\u003c/span\u003ec). Composite hydrogel No. 9, synthesized at lower acrylamide concentration c\u003csub\u003eAAm\u003c/sub\u003e=0.5 M and c\u003csub\u003eAu\u003c/sub\u003e=3 mM, contained the same large spheroidal faceted polycrystals, as well as smaller crystals\u0026thinsp;~\u0026thinsp;50 nm in size, shaped like hexagonal pyramids some of which were coalesced along the narrow interblock boundary (Fig.\u0026nbsp;\u003cspan\u003e8\u003c/span\u003e).\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec9\"\u003e\n \u003ch2\u003e3.6 Thermal analysis\u003c/h2\u003e\n \u003cp\u003eBy the example of products No. 8 and 9, the decomposition of composite hydrogels proceeded in 4 steps (Table\u0026nbsp;\u003cspan\u003e3\u003c/span\u003e, Fig.\u0026nbsp;\u003cspan\u003e9\u003c/span\u003e). The first two steps that proceeded up to ~\u0026thinsp;337\u0026deg; (No. 8)/339\u0026deg;C (No. 9) were accompanied by insignificant endo-effects and were related to the removal of volatile components from the composite. At the third step, up to ~\u0026thinsp;442\u0026deg;/421\u0026deg;C, decomposition (destruction) of the organic matrix proceeded, and exo-effect was observed. The fourth step, up to ~\u0026thinsp;667\u0026deg;/802\u0026deg;C, proceeded with a substantial exothermal effect with the maximum at 577\u0026deg;/510\u0026deg;C and corresponded to the complete combustion of carbon-containing products formed at previous steps of decomposition. No mass changes were observed during subsequent heating to 1200\u0026deg;C. Since gold content in the products did not exceed\u0026thinsp;~\u0026thinsp;0.06% as provided by synthesis conditions, the complete mass loss during heating was in fact 100%.\u003c/p\u003e\n \u003cdiv\u003e\n \u003ctable id=\"Tab3\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv\u003eTable 3\u003c/div\u003e\n \u003cdiv\u003e\n \u003cp\u003eResults of thermal analysis of products No. 8 and No. 9\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003ccolgroup cols=\"6\"\u003e\u003c/colgroup\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eProduct\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eDecomposition step\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eTemperature range, \u0026deg;C\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eMass loss, %\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eТ\u003c/em\u003e\u003csub\u003eDTG\u003c/sub\u003e, \u0026deg;C\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eТ\u003c/em\u003e\u003csub\u003eDSC\u003c/sub\u003e, \u0026deg;C\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNo. 8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eI\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e30\u0026ndash;205\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e174\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eII\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e205\u0026ndash;337\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e21\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e274\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eIII\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e337\u0026ndash;442\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e22\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e388\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eIV\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e442\u0026ndash;667\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e50\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e590\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e577\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNo. 9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eI\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e30\u0026ndash;213\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e135\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eII\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e213\u0026ndash;339\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e21\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e273\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eIII\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e339\u0026ndash;421\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e14\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e390\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eIV\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e421\u0026ndash;802\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e58\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e540\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e510\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n \u003cp\u003e\u003cem\u003eNote\u003c/em\u003e: a portion of 10.4 mg (No. 8) and 2.52 mg (No. 9);\u0026nbsp;\u003cem\u003eТ\u003c/em\u003e\u003csub\u003eDTG\u003c/sub\u003e \u0026ndash; temperature corresponding to the maximal mass loss rate at decomposition step;\u0026nbsp;\u003cem\u003eТ\u003c/em\u003e\u003csub\u003eDSC\u003c/sub\u003e \u0026ndash; temperature at which the maximal thermal effect of decomposition is achieved\u0026nbsp;\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec10\"\u003e\n \u003ch2\u003e3.7 Plasmon films\u003c/h2\u003e\n \u003cp\u003eThe films were obtained using composite hydrogel No. 8. The spectra of the film at deposition cycles 1\u0026ndash;8 are shown in Fig.\u0026nbsp;\u003cspan\u003e10\u003c/span\u003e along with growth dependences showing the changes of film extinction at specific wavelengths (\u003cem\u003eA\u003c/em\u003e\u003csub\u003e\u0026lambda;\u003c/sub\u003e) depending on the number of cycles (n) \u0026ndash; at the maximum of SPR band of nanoparticles, as well as to the left and to the right of the maximum. The intensity of spectrum increased with an increase in film thickness. Judging from the linearity of growth dependences \u003cem\u003eA\u003c/em\u003e\u003csub\u003e\u0026lambda;\u003c/sub\u003e=\u003cem\u003ea\u003c/em\u003e\u0026thinsp;+\u0026thinsp;\u003cem\u003eb\u003c/em\u003e\u0026middot;n, where \u003cem\u003ea\u003c/em\u003e and \u003cem\u003eb\u003c/em\u003e are parameters, an increment per one cycle was approximately the same in the described experiments.\u003c/p\u003e\n \u003cp\u003eTests of the effect of substrate rotation rate on film formation showed that an increase in \u0026omega; above ~\u0026thinsp;1000 rpm was unreasonable because it caused a substantial decrease in extinction increment (Fig.\u0026nbsp;\u003cspan\u003e11\u003c/span\u003e), which means also a decrease in film thickness at formation cycle because of the removal of substantial gel portion from the substrate under the action of centrifugal force.\u003c/p\u003e\n \u003cp\u003eThe transition from hydrogels to the films of dry composite containing Au NPs and PAAm and then to thin films composed of gold alone implied the necessity of thermal treatment of the samples. The spectra of composite hydrogel and its film after drying at 100\u0026deg;C, as well as after organic mass burning at 550\u0026deg;C, are compared in Fig.\u0026nbsp;\u003cspan\u003e12\u003c/span\u003e. Initial hydrogel had a spectrum with the parameters of SPR band maximum \u0026lambda;\u003csub\u003emax\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;556 nm and \u003cem\u003eA\u003c/em\u003e\u003csub\u003emax\u003c/sub\u003e=0.076. After drying, the distances between Au NPs distributed in PAAm matrix decreased, while the interaction between them increased, so that, in qualitative agreement with the theory [\u003cspan\u003e29\u003c/span\u003e, \u003cspan\u003e30\u003c/span\u003e], the position of SPR band shifted to longer wavelengths by 30 nm to \u0026lambda;\u003csub\u003emax\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;586 nm, while the intensity was conserved: \u003cem\u003eA\u003c/em\u003e\u003csub\u003emax\u003c/sub\u003e=0.076. Further burning of the matrix at high temperature seemed not to change Au NPs arrangement on substrate surface, as band position remained almost the same: \u0026lambda;\u003csub\u003emax\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;583 nm, though extinction at the maximum slightly decreased (\u003cem\u003eA\u003c/em\u003e\u003csub\u003emax\u003c/sub\u003e=0.072) because of slight band broadening. Thin Au film obtained after thermal treatment possessed high optical homogeneity. This was confirmed by the spectra of the film recorded at different sample rotation angles in the plane perpendicular to the light beam direction in the spectrophotometer (Fig.\u0026nbsp;\u003cspan\u003e12\u003c/span\u003e). Since the beam has the shape of a projection of a narrow slit of the spectrophotometer onto the sample plane, rotation of the sample in a plane perpendicular to the beam leads to the beam hitting and measuring the spectrum in different parts of the film.\u003c/p\u003e\n \u003cp\u003eDigital photographs of three films I-III after different kinds of thermal treatment are shown in Fig.\u0026nbsp;\u003cspan\u003e13\u003c/span\u003ea-c. The films were prepared from the same hydrogel (\u003cem\u003eс\u003c/em\u003e\u003csub\u003eAu\u003c/sub\u003e=3 mM, \u003cem\u003eс\u003c/em\u003e\u003csub\u003eAAm\u003c/sub\u003e=1 M) but had different thickness and therefore different extinction values. Immediately after formation and drying in the air at 100\u0026deg;C, extinction values at the maximum of individual SPR band of films were \u003cem\u003eA\u003c/em\u003e\u003csub\u003emax\u003c/sub\u003e=0.085 (I, \u0026lambda;\u003csub\u003emax\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;584 nm), 0.365 (II, 589 nm) and 0.076 (III, 586 nm). Then film III was heated at first at 380\u0026deg;C, and then at 550\u0026deg;C. Visually, the films looked thin and transparent, lilac (I, II) or pinkish (III) in color on a light background and brown on a dark background. The lines drawn on a white sheet below the films are well seen (Fig.\u0026nbsp;\u003cspan\u003e13\u003c/span\u003ea), so is the texture of a black support (Fig.\u0026nbsp;\u003cspan\u003e13\u003c/span\u003eb). The appearance of sample III* provided evidence that partial destruction of the organic matrix and its tarring took place after heating at 380\u0026deg;C (Fig.\u0026nbsp;\u003cspan\u003e13\u003c/span\u003ec). It is seen at a 10-fold magnification in the photograph of sample III after complete matrix burnoff that the film was composed of uniform granules (Fig.\u0026nbsp;\u003cspan\u003e13\u003c/span\u003ed). In addition, periodic waviness is seen, which may be due to sample rotation during film deposition using the spin-coating method.\u003c/p\u003e\n \u003cp\u003eThe SEM images of Au NPs in the dried film I were blurred because of the polymeric matrix (Fig.\u0026nbsp;\u003cspan\u003e14\u003c/span\u003ea). One can see in sharper images of annealed sample III that the film was composed of rounded particles up to ~\u0026thinsp;200 nm in diameter, distributed uniformly over the surface. Evaluation of the number of particles per unit area was ~\u0026thinsp;20 \u0026micro;m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e=2\u0026times;10\u003csup\u003e9\u003c/sup\u003e cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan\u003e14\u003c/span\u003eb). Taking into account the TEM and X-ray data, it can be assumed that the particles visible in the SEM images were clusters or islands of smaller particles (\u0026lt;\u0026thinsp;100 nm) that were recorded by TEM and, in turn, consisted of even smaller crystallites (CSR\u0026thinsp;~\u0026thinsp;20 nm).\u003c/p\u003e\n \u003cp\u003eTest experiments have shown that the obtained composite hydrogel may be used to manufacture products by means of casting. Transparent films and plates of Au NPs composite with PAAm can be obtained on smooth surfaces. A result of hydrogel casting in a mould, which was a standard cell, 1 cm in size, made of polystyrene, is shown in Fig.\u0026nbsp;\u003cspan\u003e15\u003c/span\u003e. While water was evaporated from hydrogel in the cell, the gel under drying was dragged to cell walls, and after complete drying the composite followed the shape of cell. Due to the weak adhesion of dry composite to glass and plastics, cast products are well separated from the mould. Filaments can be formed by pressing the composite hydrogel through extrusion nozzles.\u003c/p\u003e\n\u003c/div\u003e"},{"header":"4 Conclusions","content":"\u003cp\u003eA single-stage synthesis of the hybrid composite of Au NPs with polyacrylamide hydrogel from a mixture of crystal HAuCl\u003csub\u003e4\u003c/sub\u003e∙\u003cem\u003ex\u003c/em\u003eH\u003csub\u003e2\u003c/sub\u003eO, acrylamide powder, water, and a small amount of (NH\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e8\u003c/sub\u003e as additive to initiate AAm polymerization has been developed as a result of the studies. After initial reagent mixing to make a homogeneous solution, the synthesis does not require operator\u0026rsquo;s intervention. Under optimal conditions (initial concentrations: \u003cem\u003eс\u003c/em\u003e\u003csub\u003eAu\u003c/sub\u003e=3 mM, \u003cem\u003eс\u003c/em\u003e\u003csub\u003eAAm\u003c/sub\u003e=1 M, \u003cem\u003ec\u003c/em\u003e\u003csub\u003e(NH4)2S2O8\u003c/sub\u003e=1.2 mM, temperature: 60\u0026deg;C, heating time: 6 hours) a stable product is obtained, containing polycrystalline Au NPs up to ~\u0026thinsp;10\u003csup\u003e2\u003c/sup\u003e nm in size, with a clearly pronounced SPR band with the maximum at λ\u003csub\u003emax\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;552 nm. The hybrid composite may be used to obtain the plasmon films of dry Au NPs-PAAm composite or thin Au films after thermal removal of the polymer matrix. The hybrid composite is also suitable for obtaining filaments and products by the mould casting.\u003c/p\u003e \u003cp\u003eHydrogel, solid composite, and products made of it (films, plates, fibers, etc.), in particular after additional targeted chemical modification (functionalization) of Au NPs and/or PAAm matrix, may be of interest as a basis for further studies for plasmon sensorics of substances and media in chemistry and biomedicine.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e We express our gratitude to Ph.D. V.I. Zaikovsky (Boreskov Institute of Catalysis SB RAS) and Ph.D. E.A. Maksimovsky (Nikolaev Institute of Inorganic Chemistry SB RAS) for obtaining TEM and SEM images, respectively.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e This work was supported by the Russian Foundation for Basic Research (Grant No. 20-03-00017) and the Ministry of Science and Higher Education of the Russian Federation (Grant Nos. 121031700315-2 and 121031700313-8).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor Contributions\u003c/strong\u003e All authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by Vladimir Tatarchuk (synthesis, UV-visible spectroscopy data), Sergey Gromilov (XRD data) and Pavel Plyusnin (synchronous thermal analysis data). The first draft of the manuscript was written by Vladimir Tatarchuk, and all authors commented on the previous versions of the manuscript. All authors have read and approved the final manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eComplliance with ethical standards\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflict of interest\u0026nbsp;\u003c/strong\u003eThe authors declare that they have no competing interests.\u003c/p\u003e\n\u003cp\u003e\u003cbr\u003e\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eYi C, Yang Y, Liu B, He J, Nie Z (2020) Polymer-guided assembly of inorganic nanoparticles. Chem Soc Rev 49:465-508. https://doi.org/10.1039/c9cs00725c\u003cu\u003e \u003c/u\u003e\u003c/li\u003e\n\u003cli\u003eLi Z, Fan Q, Yin Y (2022) Colloidal self-assembly approaches to smart nanostructured materials. Chem Rev 122:4976-5067. https://doi.org/10.1021/acs.chemrev.1c00482 \u003c/li\u003e\n\u003cli\u003ePastoriza-Santos I, Kinnear C, P\u0026eacute;rez-Juste J, Mulvaney P, Liz-Marz\u0026aacute;n LM (2018) Plasmonic polymer nanocomposites. Nature Rev Mater 3:375-391. https://doi.org/10.1038/s41578-018-0050-7 \u003c/li\u003e\n\u003cli\u003eLi D, He Q, Li J (2009) Smart core-shell nanocomposites: Intelligent polymers modified gold nanoparticles. Adv Coll Inter Sci 149:28-38. https://doi.org/10.1016/j.cis.2008.12.007 \u003c/li\u003e\n\u003cli\u003eJiang C, Qian Y, Gao Q, Dong J, Qian W (2010) In Situ controllable preparation of gold nanorods in thermo-responsive hydrogels and their application in surface enhanced Raman scattering. J Mater Chem 20:8711\u0026ndash;8716. https://doi.org/10.1039/c0jm01582b\u003cu\u003e \u003c/u\u003e\u003c/li\u003e\n\u003cli\u003eZhan C, Moskovits M, Tian Z-Q (2020) Recent progress and prospects in plasmon-mediated chemical reaction. Matter 3:42-56. https://doi.org/10.1016/j.matt.2020.03.019\u003cu\u003e \u003c/u\u003e\u003c/li\u003e\n\u003cli\u003eGuglielmi M, Martucci A (2018) Sol-gel nanocomposites for optical applications. J Sol-Gel Sci Technol 88:551-563. https://doi.org/10.1007/s10971-018-4846-0 \u003c/li\u003e\n\u003cli\u003eWang C, Liu X, Wulf V, Vázquez-González M, Fadeev M, Willner I (2019) DNA-Based hydrogels loaded with Au nanoparticles or Au nanorods: Thermoresponsive plasmonic matrices for shape-memory, self-healing, controlled release, and mechanical applications. ACS Nano 13:3424-3433. https://doi.org/10.1021/acsnano.8b09470 \u003c/li\u003e\n\u003cli\u003eKallontzi S, Fabris L, Jitianu M, Hernandez A, Jitianu A, Klein LC (2019) Gold nanoparticles in melting gels. J Sol-Gel Sci Technol 91:189-197. https://doi.org/10.1007/s10971-019-04997-2 \u003c/li\u003e\n\u003cli\u003eWang P, Zhang L, Xia Y, Tong L, Xu X, Ying Y (2012) Polymer nanofibers embedded with aligned gold nanorods: A new platform for plasmonic studies and optical sensing. Nano Lett 12:31453150. https://doi.org/10.1021/nl301055f \u003c/li\u003e\n\u003cli\u003ePardo-Yissar V, Gabai R, Shipway AN, Bourenko T, Willner I (2001) Gold nanoparticle-hydrogel composites with solvent-switchable electronic properties. Adv Mater 13:1320-1323. https://doi.org/10.1002/1521-4095(200109)13:17\u0026lt;1320::AID-ADMA1320\u0026gt;3.0.CO;2-8 \u003c/li\u003e\n\u003cli\u003eYata T, Takahashi Y, Tan M, Nakatsuji H, Ohtsuki S, Murakami T, Imahori H, Umeki Y, Shiomi T, Takakura Y, Nishikawa M (2017) DNA nanotechnology-based composite-type gold nanoparticle immunostimulatory DNA hydrogel for tumor photothermal immunotherapy. Biomaterials 146:136-145. https://doi.org/10.1016/j.biomaterials.2017.09.014 \u003c/li\u003e\n\u003cli\u003eCorrea S, Grosskopf AK, Lopez Hernandez H, Chan D, Yu AC, Stapleton LM, Appel EA (2021) Translational Applications of Hydrogels. Chem Rev 121:11385-11457. https://doi.org/10.1021/acs.chemrev.0c01177 \u003c/li\u003e\n\u003cli\u003ePan L, Yu G, Zhai D, Lee HR, Zhao W, Liu N, Wang H, Tee BC-K, Shi Y, Cui Y, Bao Z (2012) Hierarchical nanostructured conducting polymer hydrogel with high electrochemical activity. PNAS 109:9287-9292. https://doi.org/10.1073/pnas.1202636109 \u003c/li\u003e\n\u003cli\u003eDing F, Ding H, Shen Z, Qian L, Ouyang J, Zeng S, Seery TAP, Li J, Wu G, Chavez SE, Smith AT, Liu L, Li Y, Sun L (2021) Super stretchable and compressible hydrogels inspired by hook-and-loop fasteners. Langmuir 37:7760-7770. https://doi.org/10.1021/acs.langmuir.1c00924 \u003c/li\u003e\n\u003cli\u003eLu C-H, Qi X-J, Orbach R, Yang H-H, Mironi-Harpaz I, Seliktar D, Willner I (2013) Switchable catalytic acrylamide hydrogels cross-linked by hemin-G-quadruplexes. Nano Lett 13:1298-1302. https://doi.org/10.1021/nl400078g \u003c/li\u003e\n\u003cli\u003eLiu X, Zhang J, Fadeev M, Li Z, Wulf V, Tian H, Willner I (2019) Chemical and photochemical DNA \u0026ldquo;gears\u0026rdquo; reversibly control stiffness, shape-memory, self-healing and controlled release properties of polyacrylamide hydrogels Chem Sci 10:1008-1016. https://doi.org/10.1039/c8sc04292f \u003c/li\u003e\n\u003cli\u003eZhao D, Zhu Y, Cheng W, Xu G, Wang Q, Liu S, Li J, Chen C, Yu H, Hu L (2020) A dynamic gel with reversible and tunable topological networks and performances. Matter 2:390-403. https://doi.org/10.1016/j.matt.2019.10.020 \u003c/li\u003e\n\u003cli\u003eXiao Y, Wang C, Liu K, Wei L, Luo Z, Zeng M, Yi Y (2021) Promising pure gold aerogel: in situ preparation by composite sol\u0026ndash;gel and application in catalytic removal of pollutants and SERS. J Sol-Gel Sci Technol 99:614-626. https://doi.org/10.1007/s10971-021-05597-9 \u003c/li\u003e\n\u003cli\u003eWang F, Huang Q, Su H, Cui H (2023) Self-assembling paclitaxel-mediated stimulation of tumor-associated macrophages for postoperative treatment of glioblastoma. PNAS 120:e2204621120. https://doi.org/10.1073/pnas.2204621120 \u003c/li\u003e\n\u003cli\u003eHeo YJ, Shibata H, Okitsu T, Kawanishi T, Takeuchi S (2011) Long-term in vivo glucose monitoring using fluorescent hydrogel fibers. PNAS 108:13399-13403. https://doi.org/10.1073/pnas.1104954108 \u003c/li\u003e\n\u003cli\u003eWard MA, Georgiou TK (2011) Thermoresponsive polymers for biomedical applications. Polymers 3:1215-1242. https://doi.org/10.3390/polym3031215 \u003c/li\u003e\n\u003cli\u003eDi Benedetto F, Biasco A, Pisignano D, Cingolani R (2005) Patterning polyacrylamide hydrogels by soft lithography. Nanotechnology 16:S165-S170. https://doi.org/10.1088/0957-4484/16/5/006 \u003c/li\u003e\n\u003cli\u003eBrauer G (ed) Handbook of Preparative Inorganic Chemistry (1965) New York, Acad. Press \u003c/li\u003e\n\u003cli\u003ePrescher C, Prakapenka VB (2015) DIOPTAS: a program for reduction of two-dimensional X-ray diffraction data and data exploration. High Pressure Research 35:223-230. https://doi.org/10.1080/08957959.2015.1059835\u003cu\u003e \u003c/u\u003e\u003c/li\u003e\n\u003cli\u003eKraus W, Nolze G (1996) POWDER CELL \u0026ndash; a program for the representation and manipulation of crystal structures and calculation of the resulting X-ray powder patterns. J Appl Crystallogr 29:301-303. https://doi.org/10.1107/S0021889895014920\u003cu\u003e \u003c/u\u003e\u003c/li\u003e\n\u003cli\u003eTatarchuk VV, Dobrolubova YO, Druzhinina IA, Zaikovskii VI, Gevko PN, Maksimovskii EA, Gromilov SA (2016) Facile synthesis of gold nanoparticles in aqueous acrylamide solution. Russ J Inorg Chem 61:535-543. https://doi.org/10.1134/S0036023616040203 \u003c/li\u003e\n\u003cli\u003eTatarchuk V, Druzhinina I, Zaikovskii V, Maksimovskii E, Korolkov I, Antonova O (2018) Synthesis of ZnO nanoparticles and a composite with polyacrylamide in acrylamide solutions. J Sol-Gel Sci Technol 85:66-75. https://doi.org/10.1007/s10971-017-4512-y \u003c/li\u003e\n\u003cli\u003eJiang C, Markutsya S, Tsukruk VV (2004) Collective and individual plasmon resonances in nanoparticle films obtained by spin-assisted layer-by-layer assembly. Langmuir 20:882-890. https://doi.org/10.1021/la0355085 \u003c/li\u003e\n\u003cli\u003eStorhoff JJ, Lazarides AA, Mucic RC, Mirkin CA, Letsinger RL, Schatz GC (2000) What controls the optical properties of DNA-linked gold nanoparticle assemblies? J Am Chem Soc 122:4640-4650. https://doi.org/10.1021/ja9938251 \u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"journal-of-sol-gel-science-and-technology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jsst","sideBox":"Learn more about [Journal of Sol-Gel Science and Technology](https://www.springer.com/journal/10971)","snPcode":"10971","submissionUrl":"https://submission.springernature.com/new-submission/10971/3","title":"Journal of Sol-Gel Science and Technology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"hybrid composite, gold nanoparticles, polyacrylamide hydrogel","lastPublishedDoi":"10.21203/rs.3.rs-3871911/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-3871911/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"Hybrid composites of gold nanoparticles (Au NPs) with polymer hydrogels are promising platforms for the development of new materials that can respond to external stimuli (chemical, physical, mechanical), reversibly absorb/release water and reagents, act as plasmonic sensors, and also be triggers of photochemical processes and photothermal actuators of micromechanical processes. In our study we have (1) proposed a one-step method for the synthesis of a hybrid composite of Au NPs with polyacrylamide hydrogel (PAAm) by the reduction of HAuCl 4 with acrylamide (AAm) and simultaneous radical polymerization of AAm in an aqueous solution, (2) optimized the conditions for obtaining a phase-stable product, (3) studied the effect of the initial concentrations of Au and AAm on the morphology and structure of Au NPs, (4) obtained and characterized plasmonic films from the Au NPs-PAAm composite and after thermal removal of the polymer matrix. The methods of UV-visible and photon correlation spectroscopy, X-ray diffraction, synchronous thermal analysis, transmission and scanning electron microscopy were used in the work. 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