Enhanced mid-IR detection characteristics of microplastics and nanoplastics using gold nanorods cluster at microneedle tips

Enhanced mid-IR detection characteristics of microplastics and nanoplastics using gold nanorods cluster at microneedle tips | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Enhanced mid-IR detection characteristics of microplastics and nanoplastics using gold nanorods cluster at microneedle tips Hyeyeon Hur, Cholong Kim, Ahyeon Jo, Gillhwan Kim, Jonghoon Choi, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6209048/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 2 You are reading this latest preprint version Abstract In this study, characterization of surface enhanced infrared absorption (SEIRA) spectroscopy under attenuated total reflection (ATR) mode was provided to effectively identify irregularly shaped microplastics (MPs) through mid-IR plasmon and phonon resonance effect. Here, MPs specific binding microneedle array was fabricated and examined for the mid-IR detection through surface plasmon and phonon effects out of aggregates or clusters of gold nanorods (Au NRs), which were short-range-ordered among the Au NRs spaced within sub-wavelength scale. The densely packed Au NRs clusters were embedded at microneedle’s tips, which were conjugated by a short amino acid oligo-peptide of polystyrene binding peptide (PSBP) having a strong selectivity toward PS MPs and PS nanoplastics for selective capturing or binding. For comparison, Raman spectroscopies were also adopted for accomplishment of surface enhanced Raman spectroscopy (SERS) peaks for the PS MPs. The microneedle arrays were fabricated by poly dimehtylsiloxane (PDMS) molded stamp or imprint method with commercial adhesive polymer of Norland optical adhesive (NOA). The resonant couplings between the PS MPs and the short-range-ordered Au NRs clusters were confirmed by the SEIRA peaks under both conical and pyramidal shaped microneedle formats to identify a low concentration of MPs (0.1 mg/mL) sample in PS aqueous solution. In addition, SEM images could also confirm existences of PS MPs specifically bound with PSBP conjugated Au NRs at microneedle tips. Through this study, efficient MPs detection platforms based on plasmon and phonon SEIRA effects could be newly provided for small quantity identification of MPs samples to ensure spatial resolution for many applications. Microplastics Microneedle SEIRA gold nanorods Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 1 Introduction Contamination of aquatic ecosystems with microplastics (MPs) has recently been a severe threat to human society, which has been reported through many studies [Ivleva et al. 2017; Sharma et al. 2017, Barboza et al. 2018]. For example, the MPs uptake and ingestion have been demonstrated in marine biota through feeding chain among organisms, which eventually could threaten the final predator of human beings [Sharma et al. 2017].Also, their negative impacts on the aquatic biota have been described to be fatal to living creatures, even when their size are in nano-scale [Barboza et al. 2018; Hernandez et al. 2019; Hwang et al. 2020]. Apart from environmental pollution itself, humans have been also affected hazardous aspects of by MPs [Hernandez et al. 2019; Hwang et al. 2020]. Even worse, it will be accelerated over a short period of time, and the related problems cannot be substantially ignored. Therefore, as the first step to solve this problem, a reliable sensor that selectively bind and detect MPs is urgently required [Shim et al. 2017; Nguyen et al. 2019; Shin et al. 2024]. So far, detection and quantification about the MPs have been mainly resorted to fluorescent labeling of the MPs at the first hand [Shim et al. 2017; Nguyen et al. 2019; Shin et al. 2024]. However, due to the complicated procedures to stain MPs with fluorescent media, the labeling method has been lagged. Very recently, there have been many reports about the MP detection based on vibrational spectroscopic methods. Usually, Fourier transform IR (FTIR) spectroscopy and Raman spectroscopy have been pursued and introduced [Shim et al. 2017; Nguyen et al. 2019; Shin et al. 2024; Araujo et al. 2018; Schymanski et al. 2018; Anger et al. 2019; Kniggerndorf et al. 2019; Primpke et al. 2018]. Practically, instead of the FTIR, Raman spectroscopy has been more intensively adopted for the detection of MPs [Araujo et al. 2018; Schymanski et al. 2018; Anger et al. 2019; Kniggerndorf et al. 2019]. Conventionally, it has been known that utilization of FTIR for extremely low sensing amount of target was severely limited by low IR absorption due to cross-section or length smaller than 50 mm [Shim et al. 2017; Nguyen et al. 2019]. Even worse, especially for waste MPs, their irregular surface would scatter any incident light beam to be used for the IR absorption. These obstacles have included not only shape limitation, but also analysis artefact, background effect, and resultant analysis interpretations [Shim et al. 2017; Primpke et al. 2018]. In other hand, surface enhanced IR spectroscopy (SEIRA) has been intensively proposed by an aid of metal nanoantenna’s rough surface to be applied as a sensor platform for organic material detection [Neubrech et al. 2017]. Owing to the resonant electron or plasmon oscillation within the nanoantenna, it has been continuously reported that magnitude of IR detection could be dramatically enhanced [Neubrech et al. 2017]. Utilization of plasmonic frequency of metal nanostructure or nanoantenna could be devised with the enhanced molecular vibrations of target molecules especially with organic targets including polymers. In other hand, mid-IR peak enhancements have been rare since commonly utilized nanoantenna of gold nanorods (Au NRs) have been known within VIS to near IR ranges [Stanley 2012; Zhong et al. 2015]. Typically, a sole plasmonic in mid-IR have not been widely observed and it is challenged by reasons of intrinsic noise and light emitter’s intrication [Stanley 2012; Zhong et al. 2015; Wang et al. 2020; Sahu et al. 2021; Bibikova et al. 2017; Arul et al. 2022]. In fact, traveling wave of the mid-IR known as a surface plasmon polariton (SPP) or phonon resonance should be interpreted by antenna theory and circuit analysis [Caldwell et al. 2015; Stanley 2012; Zhong et al. 2015]. In real experiment, sophisticated light control provided by waveguide have been mostly employed. However, the light of mid-IR could be confined with or without energy loss and the impedance of metal surface can be altered by adding nano-features such as slots and ridges [Stanley 2012; Zhong et al. 2015; Arul et al. 2022]. For example, using Au nanowires (NWs) or Au NRs, conjugated ligand chemicals’ peaks were successfully enhanced in its IR signals [Wang et al. 2020] and SERS and surface enhanced Raman resonance spectroscopy (SERRS) could be significantly achieved using Au NRs [Sahu et al. 2021]. Very recently, SEIRA could be obtained with Au NPs (30 nm~500 nm), which were fabricated lift-off lithography or fabricated as meta-film with stringent lattice fabrication [Bibikova et al. 2017; Arul et al. 2022]. In these reports, FTIR signals based on gold nanoclusters (Au NCs) and nanoparticles (NPs) were enhanced in peaks only under attenuated total reflection (ATR) mode. Both Au NCs and Au NPs were meta-films, which were short-range-ordered nano-structures, and the measurement setup of the ATR modes were under sub-wavelength gap in confined regions on mirror or mirror-like film such as Si wafer [Bibikova et al. 2017; Arul et al. 2022]. Meanwhile, a variety of microneedle technologies have been developed to be mainly adopted for efficient drug delivery with functions of transdermal injections of needles. Recently, the microneedle was designed to have plasmonic effect from gold nanorods (Au NRs) to detect pH by being punched and pierced into an agarose sample [Van Duyne et al. 2019]. The microneedle was replicated with Norland optical adhesive (NOA) 65 prepolymer stamping using poly dimethyl siloxane (PDMS) mold. The stamping or imprinting technology using PDMS soft-mold has been extensively developed for the patterning methodology of very delicate figures using NOA 63 or 65. Here, the microneedle-based surface enhanced Raman spectroscopy (SERS) application could open up a new era as a novel sensing platform in terms of new applicability for the microneedle [Van Duyne et al. 2019]. Very recently, approaches to accomplish selective capturing of MPs have been introduced for efficient MPs detection methods using engineered oligo-peptides, which was robustly proved by fluorescent labeling on MPs [Oh et al. 2021; Ahn et al. 2024]. Using the MPs specific binding affinities of the oligo-peptides, metal nano-structures could excite the localized surface plasmon resonance (LSPR) by sandwich binding towards MPs, which could enhance the UV-Vis wavelength absorbance of polystyrene (PS) MPs [Oh et al. 2021; Ahn et al. 2024]. In this study, the clustered Au NRs embedded at the tips of microneedle arrays were used to induce SEIRA peaks. Conjugation of polystyrene binding peptide (PSBP), which is very specifically bound to PS MPs surface, was attained by tethering PSBP on the surface of Au NRs. The Au NRs were randomly stacked at the tip of microneedle during fabrication process, where the Au NRs could be closely packed at each other and formed as a cluster to evoke the mid-IR signal enhancement. Here, closely packed Au NRs clusters were adopted as a key enabler for mid-IR emitter and the enabler typically requires a tight confinement of the light for phonon resonance. In turn, when IR spectrum is acquired under the ATR mode, the randomly spaced Au NRs and reflection prism is believed to be a source of light confinement [Arul et al. 2022]. The bindings of between PSBP and PS were subsequentially confirmed by enhanced signals of SEIRA and SERS originated from the clustered Au NRs, which were immobilized at the tip of microneedle. By taking an SEM image, we confirmed the sensing ability of the microneedles that can sense nano-sized or micro-sized plastics, which were proximate analytes of the Au NRs [Ahn et al. 2024]. Moreover, the microneedle array format in this paper will be advantageous in the sampling process of MPs or nanoplastic samples, where the needle array can have a sieving effect toward MP samples, which could reduce background signal effect. At the same time, rapid dry-up of aqueous MPs samples could be attained as well due to microneedle’s high surface energy. 2 Materials & Methods Materials Au NRs (40nm´7,000nm, >30 mg/mL in H 2 O) and dimethyl sulfoxide (DMSO, ≥99.5%) were purchased from Sigma-Aldrich. PS binding peptide (PSBP, SH-Ahx(σ-aminohexanoic acid)-HWGMWSY (His-Trp-Gly-Met-Trp-Ser-Tyr) > 80% by HPLC) was purchased from PEPTRON Co. Norland Optical Adhesive 63 (NOA 63) was purchased from Norland Product Inc. Irregularly shaped MPs samples of polystyrene (PS, > 10 mm, 75 mm < x < 106 mm sieved) were prepared by cryo-grinding method, which mimicked mechanical fragmentation of PS litter in normal environments. The PDMS microneedle molds or masters were fabricated by direct CO 2 laser ablations or replica production based on commercial pyrmidal shaped microneedle array [Kim et al. 2009; Ahn et al 2024]. Microneedle fabrication PDMS substrate was thermally cured by mixing prepolymer A and B (Silgard 189, Dupont) at 10:1 ratio (vol/vol). For a master of pyramidal microneedle array, commercially available polycarbonate (PC) based microneedle array (Smicna Pte Ltd, Singapore) was adopted to fabricate PDMS mold for imprint. For a type of pyramidal microneedle array, commercially available polycarbonate (PC) based microneedle array was adopted as a master to fabricate PDMS mold. For a conical shaped microneedle array, CO 2 laser (1080 nm, Korea stamp, PL 40) ablated PDMS pattern was formed to shape conically engraved and conditions were varied with laser intensity and IR laser speed [K im et al. 2009; Ahn et al 2024].After washing the laser-patterned PDMS mold three times with acetone and DI water, a prelolymer of NOA 63 was drop-casted on the laser engraved PDMS mold to form conical shaped microneedle array as shown in Figure 1. Then, a vacuum was applied to fill up the NOA 63 prepolymer solution into the empty region of the PSMS mold. The NOA 63 swamp could overflow the mold with temporary bubble formation. Here, identical 3-5 stampings for 3-5 min could be performed with one PDMS mold without any mechanical failure. After no bubbles were remained in the mold, the NOA 63 moiety was stamped or imprinted onto the bare glass and apply the UV light from bottom side of glass substrate for 25 min. Finally, it was baked for 10 min on a hot plate at 70 o C to completely solidify the transparent microneedle array as illustrated in Fig. 2. The Au NRs to combine PS and PSBP were applied at the first step of filling the PDMS mold to occupy tip side of microneedle. So, before using NOA 63 on mold, Au NRs was applied at the tip end of the microneedle. Au NRs solution is dropped onto the mold. Then, as described above, the mold containing Au NRs also was applied with vacuum. Since the Au NRs were dissolved in water, it is heated at 70 o C until the aqueous phase of the Au NRs solution evaporates. Conjugation of PSBP on surface of Au NRs Before sensing step of PS MPs through PSBP specific binding at the microneedle’s tip, the tip surface of the microneedle embedded with the Au NRs was oxidized using a plasma pipette (FEMTO Science, Korea) to expose the passivated Au NRs by NOA 63. Since PSBP is a peptide harboring thiol (-SH) group at N-terminal, it was efficiently conjugated to the Au NRs on the tip of the microneedle. So, the microneedle was incubated with PSBP conjugation solution at a concentration of 1mg/mL in DMSO solution and rinsed with 4 mL DI water for 25 min to remove any remained unconjugated PSBP [Oh et al. 2021; Ahn et al 2024]. The conjugation of the PSBP on Au NRs and specific binding of PS MPs on the PSBP conjugated Au NRs were identified by FTIR spectroscopy on IR card as shown in Figure S1. Detection of MPs with SEM, enhanced FTIR and Raman-spectroscopy The PSBP conjugated microneedle was cleaned three times with DI water. To attach PS MPs, the sample solutions were prepared at concentrations of 0.1 mg/mL, 1 mg/mL, 10 mg/mL, and 100 mg/mL PS MPs in DI water. The specific binding recognition and capturing process was incubated for 25 min and then washed with DI water to remove non-specifically adsorbed PS MPs. The plane scanning electron microscopy (SEM: S-4800, Hitachi, Japan) image of the Au NRs/NOA 63 microneedle showed the surface shape and length of the needle array. The sharp shape is advantageous for binding PS well and making the plasmon effect through the Au NRs antenna for strong IR peak detection. The Au NRs/NOA 63 microneedles conjugated with PSBP and selectively bound with PS MPs were applied upside-down to a flat surface of FTIR spectrometer (IRTracer-100, Shimadzu, Japan) using attenuated total reflection (ATR) module. The IR scan range was 800-4,000 cm -1 and 16 scans were averaged. Au NRs/NOA 63 microneedle, PSBP/Au NRs/NOA 63 microneedle (as control), PS/Au NRs/NOA 63 (as MP detecting sample) microneedle and PS/PSBP/Au NRs/NOA 63 microneedle have been tested in the same procedure. In the supplementary information, it can see the results of FTIR measurements of the solution at 400-4000 cm -1 . Raman spectroscopy (Raman 532ER, Wasatch Photonics, UT, USA) was measured in the range of 200-4000 cm -1 , and the Raman peak of the sample in solution as well as the microneedle sample was measured without any laser focusing tools. All the FTIR and Raman spectral measurements were conducted in ambient environment at room temperature. 3 Results and Discussion Utilization of the imprint method has not been very popular to fabricate microneedle structure [Van Duyne et al. 2019; Ahn et al. 2024]. For fabrication of microneedle PDMS molds, cost-effective methods were utilized. The CO 2 laser writer could engrave the conical shaped microneedle tips through a direct ablation of PDMS substrate and the pyramidal microneedle mold could be also adopted by using a commercially available master as shown in Figure 1.24 The imprint fabrication of NOA 63 polymeric microneedle using Au NRs targeted to SERS detection was previously reported [Van Duyne et al. 2019]. In the report, plasmon resonance at 785 nm laser was used to measure pH dependence of samples (e.g. skin) having the integrated intensity of SERS signal. In addition, the Au NRs were randomly layered at the surface of pyramidal microneedle under fixed angle of laser scattering [Van Duyne et al. 2019]. In fact, method of immobilized nanorods assembly (INRA) have been continuously developed for the SERS substrates [Ahn et al. 2024]. Moreover, by tilting optimization of microneedle’s tips at incident Raman spectrum, extinction from substrate could be minimized at least. Conventionally, the INRA has been constructed in the forms of nanopillars or nanorods to provide hotspots of SERS. However, the fabrication of nanopillars often have involved complicated process to be precisely controlled in their arrays. Therefore, in this study, aparting from common NRs’ fabrication for mid-IR signal enhancement, the Au NRs were randomly positioned to form nanocluster at the microneedle’s apex or tip by tactile fabrication protocol, where the Au NRs were closely packed to evoke a random light confinement for the mid-IR absorption as explained in Figure 1 [KarKer et al. 2015]. At the same time, in this study, the Au NRs were positioned at the tips or apex of microneedles’ tips, where very specific binding of PS MPs could be accomplished through polymer specific probe or receptor, PSBP, that were tethered to the nanoantenna of Au NRs for the plasmonic effect [Oh et al. 2021; Ahn et al. 2024]. The imprint process was illustrated in details as shown in Figure 2. Figure S2 illustrates the detection procedure protocol, where the blue bottle shapes represent for PS MPs. Here, the location of Au NRs at the microneedle tips could be very effective to have SEIRA signals at various laser exposure angles to IR scattering, which could tune the enhancement of IR signal with mechanical or geometrical controls of microneedles as shown in Fig. S2. In other word, the localization of clustered Au NRs at microneedle’s tips could be an efficient strategy for an induction of hotspots for SEIRA. As shown in a schematic diagram of Fig. S2, multi-colored peptides in helix form represent for PSBP, whose 3D shaped PSBP was a simulated shape based on the amino acid sequence. Fabrication of Microneedle with Au NRs The clustered Au NRs in this study has been the simplest nano-resonator for the plasmon and phonon excitement, which has been commercially available. Fabrication of microneedle was designed to efficiently embed Au NRs packed at the tip as shown in Figure 3(a), which could raise a chance to arrange the Au NRs perpendicular to the substrate. Since electromagnetic field of laser light, which is used as IR light source to be absorbed into detector, is not precisely vertical to the substrate, the microneedle array should be tilted and rotated to capture the maximum SEIRA signals. In fact, it has been known that IR beam scattering could be collected significantly at a specific configuration of sample geometry [Neubrech et al. 2017]. The tip was oxidized using a plasma pipette or small orifice of oxygen plasma treatment tool as illustrated in Fig. 2 to expose the Au NRs, which were buried during stamping under NOA 63. To identify the exposure of buried Au NRs’ surface to air, electron dispersed X-ray spectroscopy (EDX) analysis was performed at microneedle’s tips and Au contents were compared between before and after the O 2 plasma pipette treatments in Figure S3. Then, the oxidized part was incubated in the PSBP solution for 25 min to conjugate the thiol-functionalized PSBP. After combining of the probe peptide, sufficiently rinsing, with DI water and air gun drying were done repeatedly. Then, incubation of the microneedle tips in the PS MP solution was lasted once more for 20-25 min. In this way, the PSBP conjugated Au NRs would be a detection center, which was shown in Figure S4 for a conical shaped microneedle format for 0.1 mg/mL PS MPs sample. As shown in Figure 3(b), it was also demonstrated that PS MPs (0.1 mg/mL PS MPs sample) have been captured specifically at the tips of microneedles with pyramidal shaped format. SEM of Microneedle conjugated with PS Fig. 3(a) contains a SEM image of a pyramidal microneedle array incorporating only PSBP at the microneedle’s tip before any MP PS introduction. Fig. 3(b) show a microneedle that combines PS MPs at the tips. As shown in Fig. 3(b), PS MPs were attached only to the tips of the microneedle, where samples of different sizes of PS MPs were detected. Therefore, it was soundly proved that microneedle’s tips could capture the PS MPs regardless of the size of the MPs. As shown in the SEM images of Fig. 3(b), even though the PS MPs sample was prepared by the sieving step (75 mm < x < 106 mm), nano-szied or nano-plastics could be identified. Fig. S4 also represents that PS MPs were selectively captured at conical shaped microneedle’s tips as identified by SEM analysis. Since SEIRA’s prestigious advantage lies in an allowance of analytes at extremely low concentrations and small sizes, the SEM images in Fig. 3(b) and Fig. S4 also could prove that even small MPs (< 50 mm) selectively bound to needles’ tips could produce SERS and SEIRA signals, if their signals are appeared significantly. As a simple format of MPs detection, micro-Raman spectroscopy has been developed for the detection of MP content of drinking water having plastic bottles [Schymanski et al. 2018]. The single use bottles were contaminated by polypropylene (PP) and polyethylene terephthalate (PET).However, filtration process was required for the collection of the MPs. However, the Raman spectroscopy has been resorted to a format of microscopy to detect MPs on a flat surface. In the study, microneedle array format was adopted to identify the captured MPs to efficiently measure the target MPs with microneedle’s sieving effect as an alternative filtration process and without microscopy setup. Enhanced signal FTIR & Raman detection of MPs on Microneedle’s tips In Figure 4, FTIR spectra were obtained for the conical shaped microneedle selectively harboring the MP PS samples at the tips. For the control measurements, tip end of microneedle only with PSPB conjugation having no PS binding was measured in green line of Fig. 4. In addition, tip end of microneedle having PS MP non-specific binding incubation step without the PSBP conjugation on Au NRs were also measured and compared at the same time as shown in the Fig. 4. As shown in Fig. 4, there are no noticeable peaks about PS without the probe peptide of the PSBP on Au NRs, even though there could be non-specific binding or adsorption step with PS sample (violet line). Most IR sources are thermal emitters, which drive intrinsically broad spectra and low directionality [Stanley 2012]. However, the line widths of spectra and directionality are known to be tuned by tailoring the surface of the metal. There can be two reasons why there are no PS-related distinguishable peaks in green and violet line spectra. One is that, without the PSBP, there is no PS nano-plastics or MPs at the tip in spite that there still would be physical or Van der Waals adsorptions of PS MPs on the surface of tip. In short, there could be very small quantity of PS MPs to be physically adsorbed. However, the detection signal of the PS MPs in Fig. 4 was explicitly non-detectable low in the cases of both non-enhancement medium and antenna without any introduction of linker between Au NRs and target PS MPs. In addition, since there exist with Au NRs and NOA 63 polymeric substance, the FTIR spectra in blue line could represent for peaks about both Au NRs and NOA 63. In order to ensure the simplest protocol using the microneedle’s tips, the FTIR spectra were obtained in ATR mode under mirror-like Si wafer with down-faced position having flat surface. The detection of PS MPs could be confirmed with SEIRA peaks of MORE THAN 100 times amplified at 1450 cm -1 , 1700 cm -1 , and 1750 cm -1 as shown in Fig. 4. Unfortunately, there were no significant signal enhancement for Raman spectra with the conical shaped microneedle (data not shown). Figure 5 shows (a) ATR-FTIR and (b) Raman spectra of pyramidal shaped microneedle array harboring the PS MPs (from 0.1 mg/mL PS MPs solution) at the tips. As shown in Fig. 5(a) of FTIR spectra, most of trend spectra for samples having only PSBP without PS MPs capturing and only physically adsorbed PS MPs without the PSBP were similar throughout the entire wavenumber. However, for the microneedle’s tips having sequential conjugation of PSBP and incubation with PS MPs solution, the major peaks of the transmittance could be distinctly confirmed with amplifications at 1450 cm -1 , 1700 cm -1 , and 1750 cm -1 . Since the component of microneedle tip was based on NOA 63, which was also polymeric benzene containing material similar to PS MPs, there could be some chance to have pronounced polymeric peaks at 1450 cm -1 , 1700 cm -1 , and 1750 cm -1 even without nanoantenna like clustered Au NRs. However, there are no strong peaks for the characteristic positions. The enhanced peaks in Fig. 5(a) could be enhanced and amplified due to plasmon-polariton resonance effect of the Au NRs differently with the enhanced peaks in Fig. 4 [Caldwell et al. 2015; Stanley 2012; Zhong et al. 2015]. Therefore, it can be recognized that the tip shapes of the microneedle could affect the enhancement critically. In addition, there have been frequent issues about size limitation of MPs detection specifically with Raman spectroscopy. It has been reported that smaller MPs than 20 mm have been considered to be non-detectable in the Raman microscopy format [Anger et al. 2019]. For the Raman spectroscopy using laser irradiation, to minimize shadow effect from the microneedles’ apexes, configuration of side-illumination was found to be more effective to have high signal amplifications. In the same thread, in this study, the tilting degree for the configurations were optimized by mechanical trial-and-errors with XYZ position gauged stage. However, no direct top illumination of the 532 nm laser light was successful to have the enhanced peaks in this study. As shown in Fig. 5(b) of Raman spectra, even though there is no exact positioning peak out of PSBP at tip or apex of Au NRs, there could be still enhancement of signals from specific capturing of MPs of PS at 2950 cm -1 . When ∼1 mm sized PS MPs were examined, the peak at 3058 cm -1 was reported to be significantly detectable, which was from aromatic C-H stretch of PS MPs. As shown in Fig. 5(b), non-plasmonic Raman spectra were characterized at 1050 cm -1 , 1700 cm -1 , 2850 cm -1 , 2850 cm -1 , and 3058 cm -1 with sample of PS powder (scattered 5 mg on 0.25 cm 2 area). Particularly, the peak at 3058 cm -1 was most significantly detected with the PS powder. However, when PS nano-plastics or PS MPs were detected at the tip of microneedle, the peak at 2900 cm -1 was exclusively highlighted. In addition, apparent peaks at 1700 cm -1 and 1750 cm -1 as like as Fig. 4 and Fig. 5(a) with SEIRA results were also represented while the peak of the PS powder does not have. The peak at 1700 cm -1 was identified with both enhanced FTIR in Fig. 5 at 2855 cm -1 , 2987 cm -1 , and 3058 cm -1 and Raman in Fig. 5(b), simultaneously. The peak at 2855 cm -1 is believed to be from aliphatic C-H stretch of PS MPs [Aroujo et al. 2018; Anger et al. 2019; Kniggendorf et al. 2019]. The distinction of peaks between bare PS MPs powder and PS MPs bound to PSBP conjugated Au NRs at the microneedle clearly shows specific or exclusive detection. At the same time, the peak shifts between two PS MP samples from 3058 cm -1 to 2855 cm -1 proves the plasmonic effect out of Au NRs as well. In fact, a typical Raman spectroscopy has suffered from low sensitivity and diffraction-limited spatial resolution. As shown in Fig. 5(b), through the adoption of tip-located Au NRs microneedle, moderate spatial resolution could be achieved due to plasmonic effect and finite number of Au NRs exposed to binding towards MPs. 4 Conclusions In this paper, microneedles were fabricated by stamp or imprint process using NOA 63 embedding short-range-ordered Au NRs clusters at the microneedle tip for SEIRA detection of irregularly shaped MPs. The Au NRs edged tips could enable mid-IR sensing enhancement under ATR mode, which could have microscale gap for light confining under mirror films. The microneedle’s tips were also targeted to improve lateral resolution and fully exposed to selectively capture PS MPs using PSBP, which specifically binds at the surface of PS MPs. The SEM images taken at the tips of microneedle arrays after MPs capturing could confirm that the particle size of MPs was widely detected from 10 micrometers to 100 micrometers, which can overcome a common obstacle using ATR-FTIR. In addition, it was confirmed that SEIRA to detect MPs was successfully accomplished due to plasmon and phonon nano-resonator roles of Au NRs. This study could provide a simple and efficient nanostructure application for MPs detection to provide mid-IR signal enhancement. Since format of the microneedle is convenient to handle and carry, a quick point-of-care test for real environmental MPs contamination will be available with further development of IR measurement tool. Declarations Acknowledgment This work was conducted with the support of the Korea Environment Industry & Technology Institute (KEITI) through Ecological Imitation-based Environmental Pollution Management Technology Development Project and Measurement and funded by the Korea Ministry of Environment (MOE) (Grant number: 2019002790002). This work was also supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) grant funded by the Ministry of Education (No. 2022R1A2C1008509). 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Ivleva NP; Wiesheu AC; Niessner R (2017) Microplastic in Aquatic Ecosystems, Angew. Chem, Int. Ed. 56 : 1720-1739. https://doi.org/10.1002/anie.201606957. Karakolis EG; Nguyen B; You JB; Rochman CM; Sinton D (2019) Fluorescent Dyes for Visualizing Microplastic Particles and Fibers in Laboratory-Based Studies, Environ. Sci. Technol. Lett, 6: 334-340. https://doi.org/10.1021/acs.estlett.9b00241. Karker NA; Dharmalingam G; Carpenter MA (2015) Thermal Energy Harvesting Near-Infrared Radiation and Accessing Low Temperatures with Plasmonic Sensors, Nanoscale , 7: 17798-17804. https://doi.org/10.1039/C5NR04996A. Kim B-J; Kim H-J; Jung SM; Sung J-K; Lee HH (2009) Fabrication of Microneedle Using Laser Written PDMS Mold for Molecule Transport into Plant Skin." Biochip J. 3: 281-286. https://doi.org/10.1007/s13206-009-0034-9. Kniggendorf A-K; Wetzel C; Roth B (2019) Microplastics Detection in Streaming Tap Water with Raman Spectroscopy, Sensors 19: 1839. https://doi.org/10.3390/s19081839. Neubrech F; Huck C; Weber K; Pucci A; Giessen H (2017) Surface-Enhanced Infrared Spectroscopy Using Resonant Nanoantennas, Chem. Rev. 117: 5110-5145. https://doi.org/10.1021/acs.chemrev.6b007 Nguyen B; Claveau-Mallet D; Hernandez LM; Xu EG; Farner JM; Tufenkji N (2019) Separation and Analysis of Microplastics and Nanoplastics in Complex Environmental Samples, Acc. Chem. Res. 52: 858-866. https://doi.org/10.1021/acs.accounts.8b00602. Oh S; Hur H; Kim Y; Shin S; Woo H; Choi J; Lee HH (2021) Peptide Specific Nanoplastic Detection Based on Sandwich Typed Localized Surface Plasmon Resonance. Nanomater. 11: 2887. https://doi.org/10.3390/nano11112887. Park JE; Yonet-Tanyeri N; van Ende E; Henry A-I; White BEP; Mrksich M; Van Duyne RP (2019) Plasmonic Microneedle Arrays for in Situ Sensing with Surface-Enhanced Raman Spectroscopy (SERS) Nano Lett. 19: 6862-6868. https://doi.org/10.1021/acs.nanolett.9b02897. Primpke S; Wirth M; Lorenz C; Gerdts G (2018) Reference Database Design for the Automated Analysis of Microplastic Samples Based on Fourier Transform Infrared (FTIR) Spectroscopy, Anal. Bioanal. Chem. 410: 5131-5141. https://doi.org/10.1007/s00216-018-1156-x. Sahu BK; Dwivedi A; Pal KK; Pandian R; Dhara S; Das A (2021) Optimized Au NRs for efficient SERS and SERRS performances with molecular and longitudinal surface plasmon resonance, Appl. Surf. Sci. 537: 147615. https://doi.org/10.1016/j.apsusc.2020.147615. Schymanski D; Goldbeck C; Humpf H-U; Fürst P (2018) Analysis of Microplastics in Water by Micro-Raman Spectroscopy: Release of Plastic Particles from Different Packaging into Mineral Water, Water Res. 129: 154-162. https://doi.org/10.1016/j.watres.2017.11.011. Sharma S; Chatterjee S (2017) Microplastic Pollution, a Threat to Marine Ecosystem and Human Health: A Short Review, Environ. Sci. Pollut. Res. 24 : 21530-21537. https://doi.org/10.1007/s11356-017-9910-8. Shim WJ; Hong SH; Eo S (2017) Identification Methods in Microplastic Analysis: A Review, Anal. Meth. 9: 1384. https://doi.org/10.1039/C6AY02558G. Shin S, Jeon B, Kang W, Kim C, Choi J, Hong SC, Lee HH (2024) Characterization of microfluidic trap and mixer module for rapid fluorescent tagging of microplastics. Microfluid. Nanofluid. 28: 18 https://doi.org/10.1007/s10404-024-02716-0 Stanley R (2012) Plasmonics in the mid-infrared, Nature Photon. 6: 409-411. https://doi.org/10.1038/nphoton.2012.150. Wang D; Wang X; Lin H; Wang B; Jiang J; Li Z (2020) Surface-Enhanced Infrared Absorption of Ligands on Colloidal Gold Nanowires through Resonant Coupling, Anal. Chem. 92: 3494-3498. https://doi.org/10.1021/acs.analchem.9b04737. Zhong Y; Malagari SD; Hamilton T; Wasserman D (2015) Review of mid-infrared plasmonic materials, J. Nanophoton. 9: 093791. https://doi.org/10.1117/1.JNP.9.093791. Additional Declarations No competing interests reported. Supplementary Files SIMicroneedleSEIRAMPsNPsdetection20250312.docx Cite Share Download PDF Status: Under Review Version 1 posted Submission checks completed at journal 19 Apr, 2025 First submitted to journal 19 Apr, 2025 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. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. 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-6209048","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":445170092,"identity":"dd97c852-dfd9-485f-ba99-7607bbe79952","order_by":0,"name":"Hyeyeon Hur","email":"","orcid":"","institution":"Myongji University","correspondingAuthor":false,"prefix":"","firstName":"Hyeyeon","middleName":"","lastName":"Hur","suffix":""},{"id":445170093,"identity":"7fe32ff1-1155-44a7-9ff8-750a24fa4940","order_by":1,"name":"Cholong Kim","email":"","orcid":"","institution":"Myongji University","correspondingAuthor":false,"prefix":"","firstName":"Cholong","middleName":"","lastName":"Kim","suffix":""},{"id":445170094,"identity":"03ff6fc4-8853-4cb2-afda-79bd17f0a361","order_by":2,"name":"Ahyeon Jo","email":"","orcid":"","institution":"Myongji University","correspondingAuthor":false,"prefix":"","firstName":"Ahyeon","middleName":"","lastName":"Jo","suffix":""},{"id":445170095,"identity":"a8c7ae7a-ec43-4ad4-84ce-1e6f1ea34e97","order_by":3,"name":"Gillhwan Kim","email":"","orcid":"","institution":"Myongji University","correspondingAuthor":false,"prefix":"","firstName":"Gillhwan","middleName":"","lastName":"Kim","suffix":""},{"id":445170096,"identity":"bc06bf3c-357b-4380-8455-a113fd043c58","order_by":4,"name":"Jonghoon Choi","email":"","orcid":"","institution":"Chung-Ang University","correspondingAuthor":false,"prefix":"","firstName":"Jonghoon","middleName":"","lastName":"Choi","suffix":""},{"id":445170097,"identity":"bc68e78f-7829-4899-89be-89a4ba5c9431","order_by":5,"name":"Hyun Ho Lee","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAt0lEQVRIiWNgGAWjYBACAyBmZmCwYWBsAPMTiNaSRrqWwzA+EVrMJXLMHhdUnI9mnpHA+OEHQ1o+QS2WM3LMjWecuZ3bOCOBWbKHIceygaDDbuSYSfO2gbUwSDMwVBgQtAWq5RzYlt+kaDkA0sIGtCWHCC1nnpVJ85xJzm3sedhm2WOQRoSW48nbpHkq7HI3ticfvvGjIpmwFgaBBAht2ACKTCI0MDDwH4DQ8sQoHgWjYBSMgpEJAC/sOQ/gE+zgAAAAAElFTkSuQmCC","orcid":"","institution":"Myongji University","correspondingAuthor":true,"prefix":"","firstName":"Hyun","middleName":"Ho","lastName":"Lee","suffix":""}],"badges":[],"createdAt":"2025-03-12 06:23:15","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6209048/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6209048/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":81176837,"identity":"ae18b407-ed82-43f9-9740-a4f2cdf24634","added_by":"auto","created_at":"2025-04-23 06:29:18","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":86936,"visible":true,"origin":"","legend":"\u003cp\u003eFabrication of conical microneedle PDMS molds by direct CO\u003csub\u003e2\u003c/sub\u003e laser ablation and pyramidal master\u003c/p\u003e","description":"","filename":"1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6209048/v1/0b2783d3a590696d6f79c634.jpg"},{"id":81175978,"identity":"541950b0-57f8-4ad4-a188-39c485a54ee1","added_by":"auto","created_at":"2025-04-23 06:21:18","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":65547,"visible":true,"origin":"","legend":"\u003cp\u003eIllustration of stamp or imprint fabrication process of microneedle replica and Au NPs embedded microneedle’s tip on Si wafer or glass\u003c/p\u003e","description":"","filename":"2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6209048/v1/42721186085a294b04b1e376.jpg"},{"id":81176838,"identity":"2a67da70-366a-4e02-a45f-4e4a402ad91f","added_by":"auto","created_at":"2025-04-23 06:29:18","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":119752,"visible":true,"origin":"","legend":"\u003cp\u003eImage of NOA microneedle array (a) casted or replicated by commercial pyramidal shaped array and (b) SEM images of PS MPs captured by PSBP conjugated Au NPs cluster at microneedle’s tips\u003c/p\u003e","description":"","filename":"3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6209048/v1/76d3b125a17ffcc2d7624bbc.jpg"},{"id":81175979,"identity":"a5cf6001-28d8-4a62-b65a-dadba5561798","added_by":"auto","created_at":"2025-04-23 06:21:18","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":54087,"visible":true,"origin":"","legend":"\u003cp\u003eEnhanced FTIR spectra at tips of conical shaped microneedle array on Si wafer\u003c/p\u003e","description":"","filename":"4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6209048/v1/101bf648e16b61fdce38aed4.jpg"},{"id":81175981,"identity":"36c23bbb-4dbb-4c59-9b1a-5fd96bab80f5","added_by":"auto","created_at":"2025-04-23 06:21:18","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":90934,"visible":true,"origin":"","legend":"\u003cp\u003eFTIR and Raman peaks by Au NRs clusters at pyramidal shaped microneedle on Si wafer (a) SEIRA and (b) SERS by plasmon and phonon effect for the detection of PS MPs\u003c/p\u003e","description":"","filename":"5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6209048/v1/e64dd3a183e836885eb4e141.jpg"},{"id":81176839,"identity":"07a488e0-a485-4144-a15e-9b0c8c421934","added_by":"auto","created_at":"2025-04-23 06:29:23","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":928611,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6209048/v1/aad78763-8936-4aa5-8614-6e1270cc78e4.pdf"},{"id":81175982,"identity":"f8d332a6-7ad8-479c-a780-e022808a7b47","added_by":"auto","created_at":"2025-04-23 06:21:18","extension":"docx","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":2093641,"visible":true,"origin":"","legend":"","description":"","filename":"SIMicroneedleSEIRAMPsNPsdetection20250312.docx","url":"https://assets-eu.researchsquare.com/files/rs-6209048/v1/40331e08f1ee253ae9d06ac7.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Enhanced mid-IR detection characteristics of microplastics and nanoplastics using gold nanorods cluster at microneedle tips","fulltext":[{"header":"1 Introduction","content":"\u003cp\u003eContamination of aquatic ecosystems with microplastics (MPs) has recently been a severe threat to human society, which has been reported through many studies [Ivleva et al. 2017; Sharma et al. 2017, Barboza et al. 2018]. For example, the MPs uptake and ingestion have been demonstrated in marine biota through feeding chain among organisms, which eventually could threaten the final predator of human beings [Sharma et al. 2017].Also, their negative impacts on the aquatic biota have been described to be fatal to living creatures, even when their size are in nano-scale [Barboza et al. 2018; Hernandez et al. 2019; Hwang et al. 2020]. Apart from environmental pollution itself, humans have been also affected hazardous aspects of by MPs [Hernandez et al. 2019; Hwang et al. 2020]. Even worse, it will be accelerated over a short period of time, and the related problems cannot be substantially ignored. Therefore, as the first step to solve this problem, a reliable sensor that selectively bind and detect MPs is urgently required [Shim et al. 2017; Nguyen et al. 2019; Shin et al. 2024].\u003c/p\u003e\n\u003cp\u003eSo far, detection and quantification about the MPs have been mainly resorted to fluorescent labeling of the MPs at the first hand [Shim et al. 2017; Nguyen et al. 2019; Shin et al. 2024]. However, due to the complicated procedures to stain MPs with fluorescent media, the labeling method has been lagged. Very recently, there have been many reports about the MP detection based on vibrational spectroscopic methods. Usually, Fourier transform IR (FTIR) spectroscopy and Raman spectroscopy have been pursued and introduced [Shim et al. 2017; Nguyen et al. 2019; Shin et al. 2024; Araujo et al. 2018; Schymanski et al. 2018; Anger et al. 2019; Kniggerndorf et al. 2019; Primpke et al. 2018]. Practically, instead of the FTIR, Raman spectroscopy has been more intensively adopted for the detection of MPs [Araujo et al. 2018; Schymanski et al. 2018; Anger et al. 2019; Kniggerndorf et al. 2019].\u003c/p\u003e\n\u003cp\u003eConventionally, it has been known that utilization of FTIR for extremely low sensing amount of target was severely limited by low IR absorption due to cross-section or length smaller than 50\u0026nbsp;mm [Shim et al. 2017; Nguyen et al. 2019]. Even worse, especially for waste MPs, their irregular surface would scatter any incident light beam to be used for the IR absorption. These obstacles have included not only shape limitation, but also analysis artefact, background effect, and resultant analysis interpretations [Shim et al. 2017; Primpke et al. 2018].\u003c/p\u003e\n\u003cp\u003eIn other hand, surface enhanced IR spectroscopy (SEIRA) has been intensively proposed by an aid of metal nanoantenna’s rough surface to be applied as a sensor platform for organic material detection [Neubrech et al. 2017]. Owing to the resonant electron or plasmon oscillation within the nanoantenna, it has been continuously reported that magnitude of IR detection could be dramatically enhanced [Neubrech et al. 2017]. Utilization of plasmonic frequency of metal nanostructure or nanoantenna could be devised with the enhanced molecular vibrations of target molecules especially with organic targets including polymers.\u003c/p\u003e\n\u003cp\u003eIn other hand, mid-IR peak enhancements have been rare since commonly utilized nanoantenna of gold nanorods (Au NRs) have been known within VIS to near IR ranges [Stanley 2012; Zhong et al. 2015].\u003c/p\u003e\n\u003cp\u003eTypically, a sole plasmonic in mid-IR have not been widely observed and it is challenged by reasons of intrinsic noise and light emitter’s intrication [Stanley 2012; Zhong et al. 2015; Wang et al. 2020; Sahu et al. 2021; Bibikova et al. 2017; Arul et al. 2022]. In fact, traveling wave of the mid-IR known as a surface plasmon polariton (SPP) or phonon resonance should be interpreted by antenna theory and circuit analysis [Caldwell et al. 2015; Stanley 2012; Zhong et al. 2015]. In real experiment, sophisticated light control provided by waveguide have been mostly employed. However, the light of mid-IR could be confined with or without energy loss and the impedance of metal surface can be altered by adding nano-features such as slots and ridges [Stanley 2012; Zhong et al. 2015; Arul et al. 2022].\u003c/p\u003e\n\u003cp\u003eFor example, using Au nanowires (NWs) or Au NRs, conjugated ligand chemicals’ peaks were successfully enhanced in its IR signals [Wang et al. 2020] and SERS and surface enhanced Raman resonance spectroscopy (SERRS) could be significantly achieved using Au NRs [Sahu et al. 2021].\u003c/p\u003e\n\u003cp\u003eVery recently, SEIRA could be obtained with Au NPs (30 nm~500 nm), which were fabricated lift-off lithography or fabricated as meta-film with stringent lattice fabrication [Bibikova et al. 2017; Arul et al. 2022]. In these reports, FTIR signals based on gold nanoclusters (Au NCs) and nanoparticles (NPs) were enhanced in peaks only under attenuated total reflection (ATR) mode. Both Au NCs and Au NPs were meta-films, which were short-range-ordered nano-structures, and the measurement setup of the ATR modes were under sub-wavelength gap in confined regions on mirror or mirror-like film such as Si wafer [Bibikova et al. 2017; Arul et al. 2022].\u003c/p\u003e\n\u003cp\u003eMeanwhile, a variety of microneedle technologies have been developed to be mainly adopted for efficient drug delivery with functions of transdermal injections of needles. Recently, the microneedle was designed to have plasmonic effect from gold nanorods (Au NRs) to detect pH by being punched and pierced into an agarose sample [Van Duyne et al. 2019]. The microneedle was replicated with Norland optical adhesive (NOA) 65 prepolymer stamping using poly dimethyl siloxane (PDMS) mold. The stamping or imprinting technology using PDMS soft-mold has been extensively developed for the patterning methodology of very delicate figures using NOA 63 or 65. Here, the microneedle-based surface enhanced Raman spectroscopy (SERS) application could open up a new era as a novel sensing platform in terms of new applicability for the microneedle [Van Duyne et al. 2019].\u003c/p\u003e\n\u003cp\u003eVery recently, approaches to accomplish selective capturing of MPs have been introduced for efficient MPs detection methods using engineered oligo-peptides, which was robustly proved by fluorescent labeling on MPs [Oh et al. 2021; Ahn et al. 2024]. Using the MPs specific binding affinities of the oligo-peptides, metal nano-structures could excite the localized surface plasmon resonance (LSPR) by sandwich binding towards MPs, which could enhance the UV-Vis wavelength absorbance of polystyrene (PS) MPs [Oh et al. 2021; Ahn et al. 2024].\u003c/p\u003e\n\u003cp\u003eIn this study, the clustered Au NRs embedded at the tips of microneedle arrays were used to induce SEIRA peaks. Conjugation of polystyrene binding peptide (PSBP), which is very specifically bound to PS MPs surface, was attained by tethering PSBP on the surface of Au NRs. The Au NRs were randomly stacked at the tip of microneedle during fabrication process, where the Au NRs could be closely packed at each other and formed as a cluster to evoke the mid-IR signal enhancement. Here, closely packed Au NRs clusters were adopted as a key enabler for mid-IR emitter and the enabler typically requires a tight confinement of the light for phonon resonance. In turn, when IR spectrum is acquired under the ATR mode, the randomly spaced Au NRs and reflection prism is believed to be a source of light confinement [Arul et al. 2022].\u003c/p\u003e\n\u003cp\u003eThe bindings of between PSBP and PS were subsequentially confirmed by enhanced signals of SEIRA and SERS originated from the clustered Au NRs, which were immobilized at the tip of microneedle. By taking an SEM image, we confirmed the sensing ability of the microneedles that can sense nano-sized or micro-sized plastics, which were proximate analytes of the Au NRs [Ahn et al. 2024].\u003c/p\u003e\n\u003cp\u003eMoreover, the microneedle array format in this paper will be advantageous in the sampling process of MPs or nanoplastic samples, where the needle array can have a sieving effect toward MP samples, which could reduce background signal effect. At the same time, rapid dry-up of aqueous MPs samples could be attained as well due to microneedle’s high surface energy.\u003c/p\u003e"},{"header":"2 Materials \u0026 Methods","content":"\u003cp\u003e\u003cstrong\u003eMaterials\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAu NRs (40nm´7,000nm, \u0026gt;30\u0026nbsp;mg/mL in H\u003csub\u003e2\u003c/sub\u003eO) and dimethyl sulfoxide (DMSO,\u0026nbsp;≥99.5%) were purchased from Sigma-Aldrich. PS binding peptide (PSBP, SH-Ahx(σ-aminohexanoic acid)-HWGMWSY (His-Trp-Gly-Met-Trp-Ser-Tyr) \u0026gt; 80% by HPLC) was purchased from PEPTRON Co. Norland Optical Adhesive 63 (NOA 63) was purchased from Norland Product Inc. Irregularly shaped MPs samples of polystyrene (PS, \u0026gt; 10\u0026nbsp;mm, 75\u0026nbsp;mm \u0026lt; x \u0026lt; 106\u0026nbsp;mm sieved) were prepared by cryo-grinding method, which mimicked mechanical fragmentation of PS litter in normal environments. The PDMS microneedle molds or masters were fabricated by direct CO\u003csub\u003e2\u003c/sub\u003e laser ablations or replica production based on commercial pyrmidal shaped microneedle array [Kim et al. 2009; Ahn et al 2024].\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMicroneedle fabrication\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003ePDMS substrate was thermally cured by mixing prepolymer A and B (Silgard 189, Dupont) at 10:1 ratio (vol/vol). For a master of pyramidal microneedle array, commercially available polycarbonate (PC) based microneedle array (Smicna Pte Ltd, Singapore) was adopted to fabricate PDMS mold for imprint.\u0026nbsp;For a type of pyramidal microneedle array, commercially available polycarbonate (PC) based microneedle array was adopted as a master to fabricate PDMS mold. For a conical shaped microneedle array, CO\u003csub\u003e2\u003c/sub\u003e laser (1080 nm, Korea stamp, PL 40) ablated PDMS pattern was formed to shape conically engraved and conditions were varied with laser intensity and IR laser speed [K im et al. 2009; Ahn et al 2024].After washing the laser-patterned PDMS mold three times with acetone and DI water, a prelolymer of NOA 63 was drop-casted on the laser engraved PDMS mold to form conical shaped microneedle array as shown in Figure 1.\u003c/p\u003e\n\u003cp\u003eThen, a vacuum was applied to fill up the NOA 63 prepolymer solution into the empty region of the PSMS mold. The NOA 63 swamp could overflow the mold with temporary bubble formation. Here, identical 3-5 stampings for 3-5 min could be performed with one PDMS mold without any mechanical failure. After no bubbles were remained in the mold, the NOA 63 moiety was stamped or imprinted onto the bare glass and apply the UV light from bottom side of glass substrate for 25 min. Finally, it was baked for 10 min on a hot plate at 70 \u003csup\u003eo\u003c/sup\u003eC to completely solidify the transparent microneedle array as illustrated in Fig. 2.\u003c/p\u003e\n\u003cp\u003eThe Au NRs to combine PS and PSBP were applied at the first step of filling the PDMS mold to occupy tip side of microneedle. So, before using NOA 63 on mold, Au NRs was applied at the tip end of the microneedle. Au NRs solution is dropped onto the mold. Then, as described above, the mold containing Au NRs also was applied with vacuum. Since the Au NRs were dissolved in water, it is heated at 70 \u003csup\u003eo\u003c/sup\u003eC until the aqueous phase of the Au NRs solution evaporates.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConjugation of PSBP on surface of Au NRs\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eBefore sensing step of PS MPs through PSBP specific binding at the microneedle’s tip, the tip surface of the microneedle embedded with the Au NRs was oxidized using a plasma pipette (FEMTO Science, Korea) to expose the passivated Au NRs by NOA 63. Since PSBP is a peptide harboring thiol (-SH) group at N-terminal, it was efficiently conjugated to the Au NRs on the tip of the microneedle. So, the microneedle was incubated with PSBP conjugation solution at a concentration of 1mg/mL in DMSO solution and rinsed with 4 mL DI water for 25 min to remove any remained unconjugated PSBP [Oh et al. 2021; Ahn et al 2024]. The conjugation of the PSBP on Au NRs and specific binding of PS MPs on the PSBP conjugated Au NRs were identified by FTIR spectroscopy on IR card as shown in Figure S1.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDetection of MPs with SEM, enhanced FTIR and Raman-spectroscopy\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe PSBP conjugated microneedle was cleaned three times with DI water. To attach PS MPs, the sample solutions were prepared at concentrations of 0.1 mg/mL, 1 mg/mL, 10 mg/mL, and 100 mg/mL PS MPs in DI water. The specific binding recognition and capturing process was incubated for 25 min and then washed with DI water to remove non-specifically adsorbed PS MPs.\u003c/p\u003e\n\u003cp\u003eThe plane scanning electron microscopy (SEM: S-4800, Hitachi, Japan) image of the Au NRs/NOA 63 microneedle showed the surface shape and length of the needle array. The sharp shape is advantageous for binding PS well and making the plasmon effect through the Au NRs antenna for strong IR peak detection. The Au NRs/NOA 63 microneedles conjugated with PSBP and selectively bound with PS MPs were applied upside-down to a flat surface of FTIR spectrometer (IRTracer-100, Shimadzu, Japan) using attenuated total reflection (ATR) module. The IR scan range was 800-4,000 cm\u003csup\u003e-1\u003c/sup\u003e and 16 scans were averaged. Au NRs/NOA 63 microneedle, PSBP/Au NRs/NOA 63 microneedle (as control), PS/Au NRs/NOA 63 (as MP detecting sample) microneedle and PS/PSBP/Au NRs/NOA 63 microneedle have been tested in the same procedure. In the supplementary information, it can see the results of FTIR measurements of the solution at 400-4000 cm\u003csup\u003e-1\u003c/sup\u003e. Raman spectroscopy (Raman 532ER, Wasatch Photonics, UT, USA) was measured in the range of 200-4000 cm\u003csup\u003e-1\u003c/sup\u003e, and the Raman peak of the sample in solution as well as the microneedle sample was measured without any laser focusing tools. All the FTIR and Raman spectral measurements were conducted in ambient environment at room temperature.\u003c/p\u003e"},{"header":"3 Results and Discussion","content":"\u003cp\u003eUtilization of the imprint method has not been very popular to fabricate microneedle structure [Van Duyne et al. 2019; Ahn et al. 2024]. For fabrication of microneedle PDMS molds, cost-effective methods were utilized. The CO\u003csub\u003e2\u003c/sub\u003e laser writer could engrave the conical shaped microneedle tips through a direct ablation of PDMS substrate and the pyramidal microneedle mold could be also adopted by using a commercially available master as shown in Figure 1.24 The imprint fabrication of NOA 63 polymeric microneedle using Au NRs targeted to SERS detection was previously reported [Van Duyne et al. 2019]. In the report, plasmon resonance at 785 nm laser was used to measure pH dependence of samples (e.g. skin) having the integrated intensity of SERS signal. In addition, the Au NRs were randomly layered at the surface of pyramidal microneedle under fixed angle of laser scattering [Van Duyne et al. 2019]. In fact, method of immobilized nanorods assembly (INRA) have been continuously developed for the SERS substrates [Ahn et al. 2024]. Moreover, by tilting optimization of microneedle’s tips at incident Raman spectrum, extinction from substrate could be minimized at least. Conventionally, the INRA has been constructed in the forms of nanopillars or nanorods to provide hotspots of SERS. However, the fabrication of nanopillars often have involved complicated process to be precisely controlled in their arrays. Therefore, in this study, aparting from common NRs’ fabrication for mid-IR signal enhancement, the Au NRs were randomly positioned to form nanocluster at the microneedle’s apex or tip by tactile fabrication protocol, where the Au NRs were closely packed to evoke a random light confinement for the mid-IR absorption as explained in Figure 1 [KarKer et al. 2015].\u003c/p\u003e\n\u003cp\u003eAt the same time, in this study, the Au NRs were positioned at the tips or apex of microneedles’ tips, where very specific binding of PS MPs could be accomplished through polymer specific probe or receptor, PSBP, that were tethered to the nanoantenna of Au NRs for the plasmonic effect [Oh et al. 2021; Ahn et al. 2024]. The imprint process was illustrated in details as shown in Figure 2.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eFigure S2 illustrates the detection procedure protocol, where the blue bottle shapes represent for PS MPs. Here, the location of Au NRs at the microneedle tips could be very effective to have SEIRA signals at various laser exposure angles to IR scattering, which could tune the enhancement of IR signal with mechanical or geometrical controls of microneedles as shown in Fig. S2. In other word, the localization of clustered Au NRs at microneedle’s tips could be an efficient strategy for an induction of hotspots for SEIRA. As shown in a schematic diagram of Fig. S2, multi-colored peptides in helix form represent for PSBP, whose 3D shaped PSBP was a simulated shape based on the amino acid sequence.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFabrication of Microneedle with Au NRs\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe clustered Au NRs in this study has been the simplest nano-resonator for the plasmon and phonon excitement, which has been commercially available. Fabrication of microneedle was designed to efficiently embed Au NRs packed at the tip as shown in Figure 3(a), which could raise a chance to arrange the Au NRs perpendicular to the substrate.\u0026nbsp;Since electromagnetic field of laser light, which is used as IR light source to be absorbed into detector, is not precisely vertical to the substrate, the microneedle array should be tilted and rotated to capture the maximum SEIRA signals.\u0026nbsp;In fact, it has been known that IR beam scattering could be collected significantly at a specific configuration of sample geometry [Neubrech et al. 2017].\u003c/p\u003e\n\u003cp\u003eThe tip was oxidized using a plasma pipette or small orifice of oxygen plasma treatment tool as illustrated in Fig. 2 to expose the Au NRs, which were buried during stamping under NOA 63. To identify the exposure of buried Au NRs’ surface to air, electron dispersed X-ray spectroscopy (EDX) analysis was performed at microneedle’s tips and Au contents were compared between before and after the O\u003csub\u003e2\u003c/sub\u003e plasma pipette treatments in Figure S3. Then, the oxidized part was incubated in the PSBP solution for 25 min to conjugate the thiol-functionalized PSBP.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eAfter combining of the probe peptide, sufficiently rinsing, with DI water and air gun drying were done repeatedly. Then, incubation of the microneedle tips in the PS MP solution was lasted once more for 20-25 min. In this way, the PSBP conjugated Au NRs would be a detection center, which was shown in Figure S4 for a conical shaped microneedle format for 0.1 mg/mL PS MPs sample. As shown in Figure 3(b), it was also demonstrated that PS MPs (0.1 mg/mL PS MPs sample) have been captured specifically at the tips of microneedles with pyramidal shaped format.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eSEM of Microneedle conjugated with PS\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eFig. 3(a) contains a SEM image of a pyramidal microneedle array incorporating only PSBP at the microneedle’s tip before any MP PS introduction. Fig. 3(b) show a microneedle that combines PS MPs at the tips. As shown in Fig. 3(b), PS MPs were attached only to the tips of the microneedle, where samples of different sizes of PS MPs were detected. Therefore, it was soundly proved that microneedle’s tips could capture the PS MPs regardless of the size of the MPs. As shown in the SEM images of Fig. 3(b), even though the PS MPs sample was prepared by the sieving step (75\u0026nbsp;mm \u0026lt; x \u0026lt; 106\u0026nbsp;mm), nano-szied or nano-plastics could be identified. Fig. S4 also represents that PS MPs were selectively captured at conical shaped microneedle’s tips as identified by SEM analysis.\u003c/p\u003e\n\u003cp\u003eSince SEIRA’s prestigious advantage lies in an allowance of analytes at extremely low concentrations and small sizes, the SEM images in Fig. 3(b) and Fig. S4 also could prove that even small MPs (\u0026lt; 50\u0026nbsp;mm) selectively bound to needles’ tips could produce SERS and SEIRA signals, if their signals are appeared significantly. As a simple format of MPs detection, micro-Raman spectroscopy has been developed for the detection of MP content of drinking water having plastic bottles [Schymanski et al. 2018]. The single use bottles were contaminated by polypropylene (PP) and polyethylene terephthalate (PET).However, filtration process was required for the collection of the MPs. However, the Raman spectroscopy has been resorted to a format of microscopy to detect MPs on a flat surface. In the study, microneedle array format was adopted to identify the captured MPs to efficiently measure the target MPs with microneedle’s sieving effect as an alternative filtration process and without microscopy setup.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEnhanced signal FTIR \u0026amp; Raman detection of MPs on Microneedle’s tips\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eIn Figure 4, FTIR spectra were obtained for the conical shaped microneedle selectively harboring the MP PS samples at the tips. For the control measurements, tip end of microneedle only with PSPB conjugation having no PS binding was measured in green line of Fig. 4. In addition, tip end of microneedle having PS MP non-specific binding incubation step without the PSBP conjugation on Au NRs were also measured and compared at the same time as shown in the Fig. 4. As shown in Fig. 4, there are no noticeable peaks about PS without the probe peptide of the PSBP on Au NRs, even though there could be non-specific binding or adsorption step with PS sample (violet line). Most IR sources are thermal emitters, which drive intrinsically broad spectra and low directionality [Stanley 2012]. However, the line widths of spectra and directionality are known to be tuned by tailoring the surface of the metal.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;There can be two reasons why there are no PS-related distinguishable peaks in green and violet line spectra. One is that, without the PSBP, there is no PS nano-plastics or MPs at the tip in spite that there still would be physical or Van der Waals adsorptions of PS MPs on the surface of tip. In short, there could be very small quantity of PS MPs to be physically adsorbed. However, the detection signal of the PS MPs in Fig. 4 was explicitly non-detectable low in the cases of both non-enhancement medium and antenna without any introduction of linker between Au NRs and target PS MPs. In addition, since there exist with Au NRs and NOA 63 polymeric substance, the FTIR spectra in blue line could represent for peaks about both Au NRs and NOA 63. In order to ensure the simplest protocol using the microneedle’s tips, the FTIR spectra were obtained in ATR mode under mirror-like Si wafer with down-faced position having flat surface. The detection of PS MPs could be confirmed with SEIRA peaks of MORE THAN 100 times amplified at 1450 cm\u003csup\u003e-1\u003c/sup\u003e, 1700 cm\u003csup\u003e-1\u003c/sup\u003e, and 1750 cm\u003csup\u003e-1\u003c/sup\u003e as shown in Fig. 4. Unfortunately, there were no significant signal enhancement for Raman spectra with the conical shaped microneedle (data not shown).\u003c/p\u003e\n\u003cp\u003eFigure 5 shows (a) ATR-FTIR and (b) Raman spectra of pyramidal shaped microneedle array harboring the PS MPs (from 0.1 mg/mL PS MPs solution) at the tips. As shown in Fig. 5(a) of FTIR spectra, most of trend spectra for samples having only PSBP without PS MPs capturing and only physically adsorbed PS MPs without the PSBP were similar throughout the entire wavenumber. However, for the microneedle’s tips having sequential conjugation of PSBP and incubation with PS MPs solution, the major peaks of the transmittance could be distinctly confirmed with amplifications at 1450 cm\u003csup\u003e-1\u003c/sup\u003e, 1700 cm\u003csup\u003e-1\u003c/sup\u003e, and 1750 cm\u003csup\u003e-1\u003c/sup\u003e. Since the component of microneedle tip was based on NOA 63, which was also polymeric benzene containing material similar to PS MPs, there could be some chance to have pronounced polymeric peaks at 1450 cm\u003csup\u003e-1\u003c/sup\u003e, 1700 cm\u003csup\u003e-1\u003c/sup\u003e, and 1750 cm\u003csup\u003e-1\u003c/sup\u003e even without nanoantenna like clustered Au NRs. However, there are no strong peaks for the characteristic positions. The enhanced peaks in Fig. 5(a) could be enhanced and amplified due to plasmon-polariton resonance effect of the Au NRs differently with the enhanced peaks in Fig. 4 [Caldwell et al. 2015; Stanley 2012; Zhong et al. 2015]. Therefore, it can be recognized that the tip shapes of the microneedle could affect the enhancement critically.\u003c/p\u003e\n\u003cp\u003eIn addition, there have been frequent issues about size limitation of MPs detection specifically with Raman spectroscopy. It has been reported that smaller MPs than 20\u0026nbsp;mm have been considered to be non-detectable in the Raman microscopy format [Anger et al. 2019]. For the Raman spectroscopy using laser irradiation, to minimize shadow effect from the microneedles’ apexes, configuration of side-illumination was found to be more effective to have high signal amplifications. In the same thread, in this study, the tilting degree for the configurations were optimized by mechanical trial-and-errors with XYZ position gauged stage. However, no direct top illumination of the 532 nm laser light was successful to have the enhanced peaks in this study.\u003c/p\u003e\n\u003cp\u003eAs shown in Fig. 5(b) of Raman spectra, even though there is no exact positioning peak out of PSBP at tip or apex of Au NRs, there could be still enhancement of signals from specific capturing of MPs of PS at 2950 cm\u003csup\u003e-1\u003c/sup\u003e. When\u0026nbsp;∼1 mm sized PS MPs were examined, the peak at 3058 cm\u003csup\u003e-1\u003c/sup\u003e was reported to be significantly detectable, which was from aromatic C-H stretch of PS MPs. As shown in Fig. 5(b), non-plasmonic Raman spectra were characterized at 1050 cm\u003csup\u003e-1\u003c/sup\u003e, 1700 cm\u003csup\u003e-1\u003c/sup\u003e, 2850 cm\u003csup\u003e-1\u003c/sup\u003e, 2850 cm\u003csup\u003e-1\u003c/sup\u003e, and 3058 cm\u003csup\u003e-1\u003c/sup\u003e with sample of PS powder (scattered 5 mg on 0.25 cm\u003csup\u003e2\u003c/sup\u003e area). Particularly, the peak at 3058 cm\u003csup\u003e-1\u0026nbsp;\u003c/sup\u003ewas most significantly detected with the PS powder. However, when PS nano-plastics or PS MPs were detected at the tip of microneedle, the peak at 2900 cm\u003csup\u003e-1\u003c/sup\u003e was exclusively highlighted. In addition, apparent peaks at 1700 cm\u003csup\u003e-1\u003c/sup\u003e and 1750 cm\u003csup\u003e-1\u003c/sup\u003e as like as Fig. 4 and Fig. 5(a) with SEIRA results were also represented while the peak of the PS powder does not have. The peak at 1700 cm\u003csup\u003e-1\u003c/sup\u003e was identified with both enhanced FTIR in Fig. 5 at 2855 cm\u003csup\u003e-1\u003c/sup\u003e, 2987 cm\u003csup\u003e-1\u003c/sup\u003e, and 3058 cm\u003csup\u003e-1\u003c/sup\u003e and Raman in Fig. 5(b), simultaneously.\u003c/p\u003e\n\u003cp\u003eThe peak at 2855 cm\u003csup\u003e-1\u003c/sup\u003e is believed to be from aliphatic C-H stretch of PS MPs [Aroujo et al. 2018; Anger et al. 2019; Kniggendorf et al. 2019]. The distinction of peaks between bare PS MPs powder and PS MPs bound to PSBP conjugated Au NRs at the microneedle clearly shows specific or exclusive detection. At the same time, the peak shifts between two PS MP samples from 3058 cm\u003csup\u003e-1\u003c/sup\u003e to 2855 cm\u003csup\u003e-1\u003c/sup\u003e proves the plasmonic effect out of Au NRs as well. In fact, a typical Raman spectroscopy has suffered from low sensitivity and diffraction-limited spatial resolution. As shown in Fig. 5(b), through the adoption of tip-located Au NRs microneedle, moderate spatial resolution could be achieved due to plasmonic effect and finite number of Au NRs exposed to binding towards MPs.\u003c/p\u003e"},{"header":"4 Conclusions","content":"\u003cp\u003eIn this paper, microneedles were fabricated by stamp or imprint process using NOA 63 embedding short-range-ordered Au NRs clusters at the microneedle tip for SEIRA detection of irregularly shaped MPs. The Au NRs edged tips could enable mid-IR sensing enhancement under ATR mode, which could have microscale gap for light confining under mirror films. The microneedle\u0026rsquo;s tips were also targeted to improve lateral resolution and fully exposed to selectively capture PS MPs using PSBP, which specifically binds at the surface of PS MPs. The SEM images taken at the tips of microneedle arrays after MPs capturing could confirm that the particle size of MPs was widely detected from 10 micrometers to 100 micrometers, which can overcome a common obstacle using ATR-FTIR. In addition, it was confirmed that SEIRA to detect MPs was successfully accomplished due to plasmon and phonon nano-resonator roles of Au NRs. This study could provide a simple and efficient nanostructure application for MPs detection to provide mid-IR signal enhancement. Since format of the microneedle is convenient to handle and carry, a quick point-of-care test for real environmental MPs contamination will be available with further development of IR measurement tool.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgment\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was conducted with the support of the Korea Environment Industry \u0026amp; Technology Institute (KEITI) through Ecological Imitation-based Environmental Pollution Management Technology Development Project and Measurement and funded by the Korea Ministry of Environment (MOE) (Grant number: 2019002790002). This work was also supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) grant funded by the Ministry of Education (No. 2022R1A2C1008509).\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eAhn S, Kim N, Choi Y, Kim J, Hwang H, Kim C, Lee H-Y, Kim S, Kim JS, Lee HH, Choi J (2024) Peptide-Decorated Microneedles for the Detection of Microplastics. \u003cem\u003eBiosensors\u003c/em\u003e. 14: 140. https://doi.org/10.3390/bios14030140\u003c/li\u003e\n\u003cli\u003eAnger, P. M.; von der Esch, E.; Baumann, T.; Elsner, M.; Niessner, R.; Ivleva, N. 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Nanophoton.\u003c/em\u003e 9: 093791. https://doi.org/10.1117/1.JNP.9.093791. \u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"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":"advances-in-industrial-and-engineering-chemistry","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"Learn more about [Advances in Industrial and Engineering Chemistry](https://link.springer.com/journal/44405)","snPcode":"44405","submissionUrl":"https://submission.springernature.com/new-submission/44405/3","title":"Advances in Industrial and Engineering Chemistry","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Open","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Microplastics, Microneedle, SEIRA, gold nanorods","lastPublishedDoi":"10.21203/rs.3.rs-6209048/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6209048/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"In this study, characterization of surface enhanced infrared absorption (SEIRA) spectroscopy under attenuated total reflection (ATR) mode was provided to effectively identify irregularly shaped microplastics (MPs) through mid-IR plasmon and phonon resonance effect. Here, MPs specific binding microneedle array was fabricated and examined for the mid-IR detection through surface plasmon and phonon effects out of aggregates or clusters of gold nanorods (Au NRs), which were short-range-ordered among the Au NRs spaced within sub-wavelength scale. The densely packed Au NRs clusters were embedded at microneedle’s tips, which were conjugated by a short amino acid oligo-peptide of polystyrene binding peptide (PSBP) having a strong selectivity toward PS MPs and PS nanoplastics for selective capturing or binding. For comparison, Raman spectroscopies were also adopted for accomplishment of surface enhanced Raman spectroscopy (SERS) peaks for the PS MPs. The microneedle arrays were fabricated by poly dimehtylsiloxane (PDMS) molded stamp or imprint method with commercial adhesive polymer of Norland optical adhesive (NOA). The resonant couplings between the PS MPs and the short-range-ordered Au NRs clusters were confirmed by the SEIRA peaks under both conical and pyramidal shaped microneedle formats to identify a low concentration of MPs (0.1 mg/mL) sample in PS aqueous solution. In addition, SEM images could also confirm existences of PS MPs specifically bound with PSBP conjugated Au NRs at microneedle tips. Through this study, efficient MPs detection platforms based on plasmon and phonon SEIRA effects could be newly provided for small quantity identification of MPs samples to ensure spatial resolution for many applications.","manuscriptTitle":"Enhanced mid-IR detection characteristics of microplastics and nanoplastics using gold nanorods cluster at microneedle tips","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-04-23 06:21:13","doi":"10.21203/rs.3.rs-6209048/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"checksComplete","content":"","date":"2025-04-19T15:03:20+00:00","index":"","fulltext":""},{"type":"submitted","content":"Advances in Industrial and Engineering Chemistry","date":"2025-04-19T11:52:38+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"advances-in-industrial-and-engineering-chemistry","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"Learn more about [Advances in Industrial and Engineering Chemistry](https://link.springer.com/journal/44405)","snPcode":"44405","submissionUrl":"https://submission.springernature.com/new-submission/44405/3","title":"Advances in Industrial and Engineering Chemistry","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Open","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"26c58212-4b15-4482-93ea-29a13427cc90","owner":[],"postedDate":"April 23rd, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2025-04-28T02:23:26+00:00","versionOfRecord":[],"versionCreatedAt":"2025-04-23 06:21:13","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-6209048","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6209048","identity":"rs-6209048","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}