Molecule-Probed Raman Spectroscopy for Femtogram-per-Liter Level Per- and Polyfluoroalkyl Substances Detection

Molecule-Probed Raman Spectroscopy for Femtogram-per-Liter Level Per- and Polyfluoroalkyl Substances Detection | 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 Article Molecule-Probed Raman Spectroscopy for Femtogram-per-Liter Level Per- and Polyfluoroalkyl Substances Detection Bo Li, Liang Zhao, Jiayue Hu, Chenchi Gong, Alexis Dyke, Han Cao, and 4 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5861495/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted You are reading this latest preprint version Abstract Per- and poly-fluoroalkyl substances (PFAS) have received significant attention due to their persistence in the environment. Because of their accumulative nature, even trace amounts can adversely impact human health and ecosystems. Here, we present Molecule-Probed Raman Spectroscopy (MPRS), an ultra-sensitive, low-cost, and fast method that can achieve the femtogram-per-liter detection of PFAS, surpassing any existing methods by at least four orders of magnitude. In contrast to existing Raman Spectroscopy monitoring the spectrum of PFAS, MPRS monitors changes in the Raman spectrum of molecular probes, methyl group (-CH 3 ) on polydimethylsiloxane, upon PFAS capture. MPRS succeeds in detecting multiple individual PFAS in water and monitoring PFAS in complex matrices such as surface water and human blood. We also demonstrated the feasibility of on-site monitoring of PFAS using a portable Raman spectrometer. Beyond its transformative detection capability, MPRS establishes a new analyte detection paradigm, paving the way for innovative material systems and instruments. Physical sciences/Materials science/Materials for devices/Sensors and biosensors Physical sciences/Materials science/Techniques and instrumentation/Characterization and analytical techniques Figures Figure 1 Figure 2 Figure 3 Figure 4 Main Per- and polyfluoroalkyl substances (PFAS) are a family of synthetic organo-fluoride compounds that have been extensively utilized in various industrial and consumer applications 1 . Characterized by their strong carbon-fluorine bonds, PFAS are resistant to environmental degradation 2 – 5 and can accumulate in biological systems 6 , 7 , which raises significant concerns over their adverse effects on human health and ecological systems. Notably, exposure to PFAS from both manufacturing and inappropriate waste disposal practices has been linked to various health risks, such as cancers and pregnancy-induced hypertension 8 , 9 . As of April 2024, the United States Environmental Protection Agency (EPA) established enforceable Maximum Contaminant Levels (MCLs) for six PFAS compounds in drinking water. For instance, the individual MCL is 4 × 10 − 9 g/L for the legacy PFAS compounds, perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) 10 . However, PFAS levels of 4 × 10 − 9 g/L in drinking water will likely lead to lower levels present in blood and biological tissues 11 . Moreover, with a progressive understanding of the impact of accumulated trace-amount PFAS, the MCL could be further tightened. Therefore, it is critical to develop analytical methods with lower detection limits than the current MCL for currently available methods. The current gold standard for PFAS detection is liquid chromatography with tandem mass spectrometry (LC-MS/MS), which requires expensive instrumentation, specialized operator training, time-consuming and labor-intensive sample processing, and is cost-prohibitive for large-scale monitoring (e.g., hundreds of dollars per sample) 12 . Significant efforts have been made to develop affordable detection methods with a target of highly sensitive and fast detection of PFAS. These methods monitor the changes in optical 13 – 18 , electrical 19 , thermal 20 , electrochemical signals 21 – 26 of a substrate upon interaction with PFAS molecules. For example, a limit of detection (LOD) of 2 × 10 –12 g/L was achieved by an impedance-based electrochemical method leveraging the two-dimensional conductive metal-organic framework (MOF) with high-density metal sites for PFOA adsorption 24 . However, these methods are facing challenges such as limited sensitivity 27 , difficulty to scale up 28 , and false positivity from other substances (e.g., ions) in complex environments 29 . Raman spectroscopy captures the vibration modes of PFAS molecules, which has received immense attention for PFAS detection due to its simplicity and ease of operation 30 . A notable example is Surface-Enhanced Raman Spectroscopy (SERS), which utilizes enhanced local electromagnetic fields between noble metal nanoparticles on the substrate to amplify the Raman signals of captured PFAS molecules. However, to our best knowledge, the LODs of the SERS for PFOA detection range from 10 –10 to 10 − 5 g/L 31–34 . Moreover, the fluorescence background of PFAS has been observed (e.g., at a PFOA concentration of 0.1 g/L) to interfere with their Raman signals 35 . In addition, the price of noble metal nanoparticles and their sophisticated manufacturing process for size and spatial distribution control elevate the cost and increase the overall processing time. This study reports on a new PFAS detection mechanism, Molecule-Probed Raman Spectroscopy (MPRS). This mechanism represents a paradigm shift in Raman Spectroscopy, moving from detecting the fingerprint spectrum of the analyte to monitoring the spectrum change of molecular probes (MPs) on a substrate upon analyte capture. The baseline signal of MPRS is strong and stable as MPs are abundant and uniformly distributed on the surface of a substrate. Upon capturing PFAS, we observed an enhancement in the Raman intensity of MPs, e.g., symmetric vibration at 2902.8 cm - 1 of -CH 3 groups on a polydimethylsiloxane (PDMS) substrate. Accordingly, we achieved femtogram-per-liter level detection of perfluorooctanoic acid (i.e., 3.7 × 10 –15 g/L), surpassing the limit of detection (LOD) of SERS for PFOA detection by at least five orders of magnitude (e.g., 10 –10 to 10 − 5 g/L) 31–34 and the LOD of the gold standard, liquid chromatography with tandem mass spectrometry (LC-MS/MS) by four orders of magnitude 12 . It is important to note ultrasensitive detection of PFAS is only one example of the application of MPRS, the new mechanism will open the gate toward unlimited combinations of MPs and analytes in water and will promote new instrumentation developments in Raman spectroscopy. Principle of MPRS and PFOA detection The MPRS design is shown in Fig. 1 a. Methyl groups (-CH 3 ) on the surface of a PDMS substrate function as the molecular probe. Fluorine (F) atoms in PFAS are connected to the carbon chain through covalent bonds and impart strong electronegativity 36 . When PFAS molecules approach -CH 3 groups on the surface of PDMS, fluorine can polarize the C-H bond in methyl groups, increasing the Raman intensity of its methyl groups. In this study, PDMS is spin-coated on a SiO₂/Si wafer to achieve a molecularly flat surface (roughness ( R q ) = 0.2 nm, Supplementary Fig. S1 ). Confocal Raman microscope (CRM) is used to focus on the surface of PDMS and capture the changes in PDMS spectrum upon PFAS adsorption. To ensure uniform adsorption of PFAS on the surface of PDMS, we utilized a combined dipping (average speed = 1.5 m/min) and sonication (40 kHz and 60 W) process for 10 min ( t adsorption = 10 min). The substrate was submerged in the solution during the entire PFAS adsorption process. The dipping creates a shear field to facilitate a uniform deposition of PFAS, while the sonication in PFAS solution not only helps to maintain well-dispersed PFAS molecules but also energizes PFAS to achieve fast deposition 37 – 39 . As a proof of concept, we first chose perfluorooctanoic acid (PFOA) dissolved in deionized (DI) water with a concentration ( C PFOA ) of 2.8 × 10 − 9 g/L. The PDMS substrate with adsorbed PFOA (PFOA@PDMS) was rinsed with DI water and dried under nitrogen. CRM measurement conditions are fixed unless mentioned otherwise (i.e., ×50 lens, 532 nm wavelength for laser excitation, 3 mW for laser power, 10 seconds for integration time, and accumulation time of 1). Figure 1 b compares the Raman spectra of PDMS and PFOA@PDMS. While most of the characteristic peaks of PDMS remain overlapping, the peak intensity ( I ) of symmetric stretching vibration of methyl groups ( ν s (-CH 3 ), 2902.8 cm − 1 ) increases by 280 counts compared to its intensity of pristine PDMS ( I 0 ) with a Raman intensity enhancement ( \(\:{R}_{\text{E}}=(I-{I}_{0})/{I}_{0}\) ) of 5.9%. Even for a shorter adsorption time ( t adsorption = 2 min), we can still achieve a R E of 1.6% (Supplementary Fig. S2a). It is interesting to know that R E has not shown notable changes within a wide range of laser power (e.g., 1 to 5 mW), demonstrating the excellent stability and tolerance of MPRS against changing measurement conditions (Supplementary Fig. S3). Both R E values at t adsorption = 2 min and 10 min are significantly larger than the instrument noise (0.5%), determined by monitoring the ν s (-CH 3 ) stretching peak at 2902.8 cm − 1 for 200 detecting cycles with an interval of 2 seconds between cycles (Supplementary Fig. S4). To verify that the signal enhancement was truly due to the adsorption of PFOA, time-of-flight secondary ion mass spectrometry (ToF-SIMS) was performed. The results demonstrate a uniform distribution of F element by capturing the ionized state of PFOA (i.e., F − ) (Fig. 1 c and 1 d, Supplementary Fig. S2b, Supplementary Fig. S2c, and Supplementary Fig. S5). It should be noted that a slight increase ( R E = 1.1%) of asymmetric methyl groups ( ν as (-CH 3 ), 2964.4 cm − 1 ) can be found, suggesting a similar fluorine-induced polarization mechanism may be applied to other vibration modes (Supplementary Fig. S6). Here, we focus on ν s (-CH 3 ) stretching at 2902.8 cm − 1 due to its larger signal-to-noise ratio to clarify the effectiveness and mechanism of MPRS. PFAS detection capabilities of MPRS Figure 2 elucidates the detection capabilities of MPRS. As shown in Fig. 2 a, the influence of PFOA concentration on the R E was illustrated at two adsorption times (i.e., t adsorption = 10 min and 2 min). Controls with PFOA (i.e., 2.8 × 10 − 7 g/L) or without PFOA in DI water were measured by MPRS and validated using LC-MS/MS (Supplementary Table S1 ). For t adsorption = 10 min (square), a linear relationship between R E and logarithmic PFOA concentrations (i.e., 2.8 × 10 − 1 to 2.8 × 10 − 17 g/L) was observed down to 2.8 × 10 − 17 g/L and then the curve reaches a plateau. A similar plateau is reached for the curve with t adsorption = 2 min (circle) when the concentration reaches 2.8 × 10 − 13 g/L and lower. This plateau matches the Raman enhancement ( R E = 0.6%) of PDMS dipped in pure DI water, which is considered the blank sample. Therefore, we defined R E = 0.6% as the water background (Supplementary Fig. S7). The LOD of MPRS can be determined using the concentration corresponding to three-fold water background (blank) in the linear fitting curve. Specifically, a LOD of 3.7 × 10 − 15 g/L for PFOA can be achieved for t adsorption = 10 min, which is 6 orders of magnitude lower than the current MCL (i.e., 4 ×10 − 9 g/L) 10 . For a fast detection with t adsorption = 2 min, we can still achieve a LOD of 4.3 × 10 − 9 g/L for PFOA. The comparison of the two curves shows that longer adsorption time leads to higher R E at the same concentration. If R E only originates from the interfacial interaction between -CH 3 on PDMS and -CF 2 /-CF 3 on PFOA, a plateau should be reached when the surface of PDMS is fully covered with PFAS. To validate this hypothesis, we increased the adsorption time (1 min to 30 min) at a fixed concentration (e.g., C PFOA = 2.8 × 10 − 9 g/L). We found the peak intensity reaches a plateau at t adsorption = 20 min as shown in Fig. 2 b. Further adsorption of PFAS on top of the existing PFAS layer could not polarize the molecular probes on PDMS due to the increased distance. To further explore MPRS detection capabilities, we investigated the response of four additional PFAS: perfluorobutanoic acid (PFBA), perfluorooctane sulfonates (PFOS), perfluorobutane sulfonate (PFBS), and hexafluoropropylene oxide dimer acid (GenX), at a concentration of 2.8 × 10 − 9 g/L (Fig. 2 c). According to the ToF-SIMS results presented in Supplementary Fig. S8, we first confirmed the uniform deposition of each PFAS onto the PDMS surface after 10 min adsorption. Although all PFAS can induce the Raman enhancement of ν s (-CH 3 ) peak at 2902.8 cm − 1 , the magnitudes of R E vary with different chain lengths and head groups. The PFAS with the same carbon chain length shows similar R E (e.g., PFOA (5.9%) and PFOS (6.8%)), whereas the R E of PFBA and PFBS are much smaller (e.g., PFBA (2.7%) and PFBS (2.6%)). The decrease in R E values can be explained by the lower partition coefficients ( K D ) of shorter-chain PFAS than longer-chain PFAS, which increases the hydrophilicity 40 , 41 . The R E of GenX is smaller than those of PFOA and PFOS which can be attributed to the increased hydrophilicity from a shorter carbon chain and additional oxygen atoms in the backbone. The advantage of MRPS is elaborated in Fig. 2 d and Supplementary Table S2, where the processing time and LOD among different PFOA detection methods are compared. It is important to note processing procedures vary drastically for different methods. However, the overall processing time should include the sample preparation time and detection time. For MPRS, the sample preparation includes substrate preparation (e.g., 1 min for spin coating PDMS + 5 min for PDMS curing) and PFAS adsorption (e.g., t adsorption = 2–10 min). The detection time of the Raman spectrum is 1–5 min depending on how many sampling points are surveyed. By contrast, the LC-MS/MS method (e.g., Methods 533, 537, and 537.1) has more than five sample preparation procedures, which take hours to days according to the equipment manual 42 – 44 . Unfortunately, since there is no standard to document the time for each procedure, to simplify the comparison in Fig. 2 d, the processing time for LC-MS/MS is set to be 24 hours and for all other methods, PFAS adsorption time ( t adsorption ) is used to compare the processing time. Similar to processing time, the definition of LOD varies with different methods as summarized in Supplementary Table S2. Still, the comparison suggests the LOD of MPRS is far superior to existing methods. It is 3 orders of magnitude lower than the state-of-the-art results from LC-MS/MS (and LC/MS/MS) with a processing time of at least 2 orders of magnitude shorter. Compared to SERS, MPRS is 5 orders of magnitude more sensitive. Moreover, MPRS can be more affordable than SERS as the substrate of MPRS is made of commercial polymer, whereas SERS requires a sophisticated and time-consuming metal deposition process. Detection mechanism The PFAS detection mechanism is revealed through a combination of classical molecular dynamics (MD) simulations and quantum ab-initio calculations using PFOA as an example. MD simulations analyze the adsorption process and energetics, providing molecular configurations for ab-initio calculations, which then explore the change of electronic structures in the -CH 3 group of PDMS as PFOA approaches. Figure 3 A illustrates the adsorption process of 50 PFOA molecules onto a PDMS substrate in water. The detailed parameter set-up can be found in Supplementary Table S3. The center of mass (COM) of the PFOA molecular cluster is initially positioned at z = 20.00 Å above the PDMS surface (see Fig. 3 b for the definition of the surface). Due to the hydrophobic nature of the difluoromethyl (-CF 2 ) and trifluoromethyl (-CF 3 ) groups, neighboring PFOA molecules coalesce into clusters and move towards the hydrophobic PDMS surface. After 20 ns, the system reaches equilibrium, with the PFOA molecules dispersing across the PDMS surface and the COM settling at z = 0.97 ± 0.23 Å. Molecular trajectories indicate that PFOA molecules tend to align parallel to the PDMS surface (Supplementary Fig. S9). In this configuration, the -CF 2 and -CF 3 groups of PFOA are strongly attracted to the methyl (-CH 3 ) groups of PDMS, while the head groups (i.e., -COOH) of PFOA orient away from the hydrophobic substrate (see Supplementary Fig. S10 for three examples of the molecular configuration). Indeed, a molar density plot (Fig. 3 b) reveals that F has a peak density of 38.83 mol/L at z = 0.76 Å, very close to PDMS, while O peaks at 3.65 mol/L at z = 3.36 Å indicating a greater distance. The close methyl-fluorocarbon interaction strongly governs the adsorption and detection of PFOA. As depicted in Fig. 3 c, the system’s potential energy decreases as PFOA approaches the PDMS substrate, confirming a thermodynamically favorable adsorption process. Notably, PFOA molecules are ionized in the aqueous environment. Our MD simulations show that ionic and neutral PFOA exhibit similar adsorption processes and results (Supplementary Fig. S11). The PFOA detection mechanism is further explored through quantum ab-initio calculations. Figure 3 d illustrates the local charge density difference near the -CH 3 group of PDMS before and after PFOA adsorption. The iso-surfaces represent a charge density difference level of 0.0005 Bohr − 3 . Since F atoms have a significantly higher electronegativity than H atoms, electrons associated with the -CH 3 group of PDMS and the -CF 3 group of PFOA tend to shift closer to the F atoms. An electron accumulation region then forms near the F atoms in the -CF 3 group, while an electron depletion region appears between the -CH 3 and -CF 3 groups. This redistribution of electrons alters the electronic structure in the C-H bond, causing local polarization of charge density within the -CH 3 group. Multiple optimized adsorption configurations were examined, all yielding consistent results (Supplementary Fig. S12). Figure 3 e presents a planar charge density color map that quantitatively reveals changes in the electronic structure of -CH 3 as it serves as a molecular probe for PFAS detection. The charge density map is plotted in a plane formed by two bonds, C-H1 and C-H2, as illustrated in the inset of Fig. 3 e. The C-H1 bond is strongly attracted by and the closest to the -CF 3 group, while the other two bonds (C-H2 and C-H3) are less affected. Due to the strong interaction with PFOA, the C-H1 bond develops a dumbbell-shaped charge density profile, showing significant changes compared to its state before PFOA adsorption (Supplementary Fig. S13). In contrast, the charge density near the C-H2 bond remains largely unchanged. These results demonstrate that the approaching C-F bonds in PFOA redistribute electrons in the -CH 3 groups of PDMS, particularly along the C-H bond closest to PFOA. The density of states (DOS) was further calculated to investigate how PFOA adsorption affects the electronic structure of the -CH 3 group in PDMS. Total and partial DOS curves for PDMS are presented in Fig. 3 f. The bandgap of pristine PDMS was found to be 4.89 eV, consistent with its insulating nature. According to the total DOS, after PFOA adsorption, small peaks appear below the bottom of the conduction band (CB), and the top edge of CB decreases. Partial DOS is further analyzed to pinpoint the influence on each atom in the -CH 3 group. In the valence band (VB), the C 2p orbitals are prevalent in the upper portion of the VB, whereas both H 1s and C 2p orbitals contribute to the lower portion of the VB, indicating strong covalence connection between the C and H atoms. After PFOA adsorption, PFOA alters the distribution of H 1s and C 2p states between − 4.69 eV and − 1.26 eV; and both H 1s and C 2p orbitals tend to occupy higher energy levels. In the CB, the C 2p orbitals are prevalent. After PFOA adsorption, the CB is shortened from 4.99 eV to 3.45 eV, while the bottom edge of CB remains unchanged. The changes in DOS and charge density distribution account for the distinct features of -CH 3 groups in the Raman scattering spectra before and after PFOA adsorption 45 . PFOA detection in real scenarios In real scenarios, PFAS detection faces challenges such as false positive signals from non-PFAS species and the requirement of on-site data collection in real-time (Fig. 4 a). We first examined the PFAS selectivity of MPRS against ions, which are common compositions of environmental water samples and human biological samples. The R E of salt/DI water solutions at 1 mM with various salts (0.6% for CaCl 2 to 0.8% for Na 2 SO 4 ) without PFOA is comparable to the water background (0.6%), suggesting limited interactions between ions and molecular probes (-CH 3 ) (Supplementary Table S4). On the other hand, adding salts (e.g., NaCl) to a PFOA-spiked DI water solution may show the difference. Figure 4 b shows the R E evolution obtained in a PFOA-spiked aqueous solution with different NaCl salt concentrations ( C NaCl ). In all tested salt/DI water systems, R E values follow linear regression (versus logarithmic C PFOA ). Adding 1 mM NaCl into a PFOA-spiked aqueous solution does not significantly change the linear regression slope compared to the case without NaCl. But higher NaCl concentrations (10 mM to 1000 mM) lead to higher slopes. Further analysis (Supplementary Fig. S14) shows a linear regression between slope and C NaCl (in logarithmic scale), demonstrating that NaCl salt can increase the adsorption efficiency of PFOA on PDMS. A similar phenomenon can be found in other salt-PFOA or mixed salt-PFOA systems (Supplementary Fig. S15). As a result, we can conclude that salts alone in aqueous solution (without PFOA) will not create a false positive signal. Instead, salts favorably enhance the interaction between PFOA and PDMS through a salting-out effect and increase the PFAS adsorption rate 40 , 46 , thereby increasing the R E . Also, the linear relationship of both R E -logarithmic C PFOA and slope-logarithmic C NaCl curves suggest the influence of salt can be predicted and calibrated. We further evaluated the MPRS performance in surface water (SW) and human blood spiked with different PFOA concentrations (the detailed processing information and real sample images can be found in Methods and Supplementary Fig. S16). These two systems are enriched with different ions and other possible contaminants. We first examined a possible R E value in SW solution without spiking PFOA. The result displays a R E (0.6 ± 1.4%, Supplementary Fig. S17) similar to the water background (Supplementary Fig. S6) suggesting no detectable PFAS in SW. Moving forward, we spiked different concentrations of PFOA into SW. As shown in Fig. 4 c, we obtained a linear correlation (slope = 0.31, r 2 = 0.96) of R E with increasing PFOA concentrations. The cation, anion, and other component concentrations in SW were summarized in Supplementary Table S5-S8. This slope is higher than the case in the PFOA/DI water system (Fig. 2 a), further elaborating that salts in SW can enhance the adsorption of PFOA on PDMS. Compared to SW, human blood is a combination of water, proteins, salts (especially Fe cations), and cells. PFOA-spiked human blood samples from 3 volunteers were examined. As shown in Fig. 4 d, two PFOA concentrations (2.8 × 10 − 9 and 2.8 × 10 − 1 g/L) were tested and R E values are significantly higher than the instrument noise (0.5%) and its corresponding pure blood backgrounds for blood samples from all three volunteers. Furthermore, we validate the potential of on-site PFAS detection using portable Raman (Fig. 4 e). Here, the laser power is increased to 50 mW and t adsorption is 2 min. A linear enhancement curve can be obtained from PFOA-spiked aqueous solutions with a concentration range from 2.8 × 10 − 12 g/L to 2.8 × 10 − 6 g/L. Compared with CRM, portable Raman can focus on the surface, but the signal of some PDMS molecules underneath the surface (not in direct contact with PFOA molecules) will be collected. However, the enhanced signal is still strong enough to differentiate the concentration of PFOA. Conclusions MPRS represents an affordable Raman detection strategy for ultrasensitive and fast detection of PFAS that meets a critical need for protecting the environment and human health as well as for implementing environmental regulation. MPRS can detect the concentration of a solution with a single known PFAS species as well as in complex systems such as surface water and blood. It should be noted that selectivity remains a challenge for MPRS when differentiating PFAS species in a multi-PFAS mixed solution. The discovery of new MPs targeting the head groups of PFAS could be a potential solution. Moreover, the integration of MPRS with other analytical methods including existing Raman spectroscopies could be a key for future development to realize both high sensitivity and selectivity. Most importantly, MPRS opens a new realm of innovation in water pollutant detection and Raman spectroscopy. From a material perspective, there is an unlimited design space for new combinations of MPs and analytes. From an instrumentation perspective, MPRS will promote the development of MP-decorated substrate manufacturing, narrow-band spectrum modules for specific MPs, and new portable and deployable testing platforms. Declarations Competing interests B.L., L.Z., W.X., and C.G. filed a U.S. Provisional Patent. The remaining authors declare no competing interests. Author contributions Conceptualization: L.Z., B.L.; Data curation: L.Z., J.H., C.G., A.D.; Formal analysis: L.Z., J. H., C.G., H.C., L.L., W.X., B.L.; Funding acquisition: W.X., B.L.; Investigation: L.Z., J.H., C.G., W.X., B.L.; Methodology: L.Z., J.H., C.G., A.D., H.C., J.W.; Project administration: L.L., W.X., B.L.; Supervision: L.L., W.X., B.L.; Visualization: L.Z., L.L., W.X., B.L.; Writing-original draft: L.Z., J.H., C.G., H.C., J.W., L.B., L.L., W.X., B.L.; Writing-review & editing: L.Z., J.H., J.W., L.B., L.L., W.X., B.L.. Acknowledgements We thank Dr. Gang Feng and Dr. Scott Dietrich at Villanova University for the support of Raman and AFM measurement; Dr. Xu Feng at the University of Delaware for the assistance and discussion with ToF-SIMS; and Dr. Sumbul Hafeez at Villanova University for the discussion on PFAS solution preparation. We also thank Mr. Rahul Sharma in Anton Paar USA, Inc. for the use of the portable Raman (Anton Paar CORA 5001 Raman spectrometer). L.Z., C.G., and B.L. were supported in part by the U.S. National Science Foundation (Grants # AM-2003077 and MRI-2018852). C. G., W.X., and B.L., acknowledge the support from the Dean’s Fellow of the College of Engineering, Villanova University. A.D. acknowledges the support from ME Junior Research Scholar, Department of Mechanical Engineering, Villanova University. L.B., J.W., and W.X. were funded in part by the Villanova University Research Catalyst Award. W.X. would like to acknowledge support by the U.S. Department of Defense through the Strategic Environmental Research and Development Program (SERDP ER23-3593). References Glüge, J. et al. An overview of the uses of per- and polyfluoroalkyl substances (PFAS). Environ. Sci. Proc. Imp. 22 , 2345-2373 (2020). Evich, M. G. et al. Per-and polyfluoroalkyl substances in the environment. Science 375 , eabg9065 (2022). Xiao, F. et al. Cross-national challenges and strategies for PFAS regulatory compliance in water infrastructure. Nat. Water 1 , 1004-1015 (2023). Gao, J. et al. Photochemical degradation pathways and near-complete defluorination of chlorinated polyfluoroalkyl substances. Nat. Water 1 , 381-390 (2023). Tokranov, A. K. et al. Predictions of groundwater PFAS occurrence at drinking water supply depths in the United States. Science 386 , 748-755 (2024). Chen, X. et al. Quantifying indirect contribution from precursors to human body burden of legacy PFASs based on paired blood and one-week duplicate diet. Environ. Sci. Technol. 56 , 5632-5640 (2022). Brunn, H. et al. PFAS: forever chemicals-persistent, bioaccumulative and mobile. Reviewing the status and the need for their phase out and remediation of contaminated sites. Environ. Sci. Eur. 35 , 20 (2023). Nicole, W. (National Institute of Environmental Health Sciences, 2013). Luo, Y. et al. Prenatal exposure of PFAS in cohorts of pregnant women: identifying the critical windows of vulnerability and health implications. Environ. Sci. Technol. 58 , 13624−13635 (2024). Read, R., Briefs, C. B. & Cases, C. C. C. PFAS National Primary Drinking Water Regulation 89 Fed. Reg. 32532 (Apr. 26, 2024) Copy Cite. Federal Register (2024). Poothong, S., Thomsen, C., Padilla-Sanchez, J. A., Papadopoulou, E. & Haug, L. S. Distribution of novel and well-known poly-and perfluoroalkyl substances (PFASs) in human serum, plasma, and whole blood. Environ. Sci. Technol. 51 , 13388-13396 (2017). Al Amin, M. et al. Recent advances in the analysis of per-and polyfluoroalkyl substances (PFAS)-A review. Environ. Technol. Innov. 19 , 100879 (2020). Dalapati, R., Hunter, M., Sk, M., Yang, X. & Zang, L. Fluorescence turn-on detection of perfluorooctanoic acid (PFOA) by perylene diimide-based metal-organic framework. ACS Appl. Mater. Interfaces 16 , 32344−32356 (2024). Zhang, K. et al. Luminescence life time-based sensing platform based on cyclometalated Iridium (III) complexes for the detection of perfluorooctanoic acid in aqueous samples. Anal. Chem. 96 , 1565-1575 (2024). Chen, Q., Zhu, P., Xiong, J., Gao, L. & Tan, K. A sensitive and selective triple-channel optical assay based on red-emissive carbon dots for the determination of PFOS. Microchem. J. 145 , 388-396 (2019). Concellón, A., Castro-Esteban, J. & Swager, T. M. Ultratrace PFAS detection using amplifying fluorescent polymers. J. Am. Chem. Soc. 145 , 11420-11430 (2023). Zheng, Z. et al. Guanidinocalix [5] arene for sensitive fluorescence detection and magnetic removal of perfluorinated pollutants. Nat. Commun. 10 , 5762 (2019). Concellón, A. & Swager, T. M. Detection of per‐and polyfluoroalkyl substances (PFAS) by interrupted energy transfer. Angew. Chem. Int. Ed. 62 , e202309928 (2023). Park, S., Gordon, C. T. & Swager, T. M. Resistivity detection of perfluoroalkyl substances with fluorous polyaniline in an electrical lateral flow sensor. Proc. Nat. Acad. Sci. USA 121 , e2317300121 (2024). Tabar, F. A. et al. Thermal determination of perfluoroalkyl substances in environmental samples employing a molecularly imprinted polyacrylamide as a receptor layer. Environ. Technol. Innov. 29 , 103021 (2023). Mashkoor, F. et al. Freestanding WS 2 -MWCNT nanocomposite for electrochemical detection of contaminants of emerging concern-perfluorooctanoic acid “A Forever Chemical” and supercapacitor applications. ACS Sustain. Chem. Eng. 11 , 13306-13319 (2023). Tian, Q. et al. Fluorine-functionalized MOF modified GCE for highly sensitive electrochemical detection of persistent pollutant perfluorooctanoic acid. Sensor. Actuat. B-Chem. 404 , 135309 (2024). Shanbhag, M. M. et al. Hafnium doped tungsten oxide intercalated carbon matrix for electrochemical detection of perfluorooctanoic acid. Chem. Eng. J. 434 , 134700 (2022). Gumyusenge, A. et al. Copper-based 2D conductive metal organic framework thin films for ultrasensitive detection of perfluoroalkyls in drinking water. (2022). Hafeez, S., Khanam, A., Cao, H., Chaplin, B. P. & Xu, W. Novel conductive and redox-active molecularly imprinted polymer for direct quantification of perfluorooctanoic acid. Environ. Sci. Technol. Lett. 11 , 871-877 (2024). Comnea-Stancu, I. R. & van Staden, J. K. F. Ultrasensitive detection of water pollutant PFOA based on AuNPs decorated NiOScZ screen-printed electrode. J. Environ. Chem. Eng. 12 , 113850 (2024). Menger, R. F., Funk, E., Henry, C. S. & Borch, T. Sensors for detecting per-and polyfluoroalkyl substances (PFAS): A critical review of development challenges, current sensors, and commercialization obstacles. Chem. Eng. J. 417 , 129133 (2021). Garg, S. et al. Nano-enabled sensing of per-/poly-fluoroalkyl substances (PFAS) from aqueous systems-A review. J. Environ. Manag. 308 , 114655 (2022). Wang, Y., Darling, S. B. & Chen, J. Selectivity of per-and polyfluoroalkyl substance sensors and sorbents in water. ACS Appl. Mater. Interfaces 13 , 60789-60814 (2021). Prakash, J. Ultrasensitive detection of emerging water contaminants using surface enhanced Raman scattering technique: Recent advancement, challenges and future prospects. Curr. Opin. Environ. Sci. Health 39 , 100552 (2024). Li, C., Fang, X., Li, H. & Zhang, X. Direct and rapid sensing of per-and polyfluoroalkyl substances using SERS-active optical fibers. ACS Appl. Opt. Mater. 2 , 610-616 (2024). Feng, Y. et al. Ag nanoparticle/Au@Ag nanorod sandwich structures for SERS-based detection of perfluoroalkyl substances. ACS Appl. Nano Mater. 6 , 13974-13983 (2023). Park, H., Park, J., Kim, W., Kim, W. & Park, J. Ultra-sensitive SERS detection of perfluorooctanoic acid based on self-assembled p-phenylenediamine nanoparticle complex. J. Hazard. Mater. 453 , 131384 (2023). McDonnell, C. et al. Aerosol jet printed surface-enhanced Raman substrates: application for high-sensitivity detection of perfluoroalkyl substances. ACS Omega 8 , 1597-1605 (2022). Bai, S. et al. Plasmonic superstructure arrays fabricated by laser near-field reduction for wide-range sers analysis of fluorescent materials. Nanomaterials 12 , 970 (2022). Krafft, M. P. & Riess, J. G. Chemistry, physical chemistry, and uses of molecular fluorocarbon-hydrocarbon diblocks, triblocks, and related compounds-Unique “Apolar” components for self-assembled colloid and interface engineering. Chem. Rev. 109 , 1714-1792 (2009). Zhao, L. et al. Wafer-scale full-coverage self-limiting assembly of particles on flexible substrates. ACS Appl. Mater. Interfaces 14 , 46095-46102 (2022). Zhou, D. et al. Ultrafast assembly and healing of nanomaterial networks on polymer substrates for flexible hybrid electronics. Appl. Mater. Today 22 , 100956 (2021). Zhou, D. et al. Ultrafast assembly and healing of nanomaterial networks on polymer substrates for flexible hybrid electronics. ACS Appl. Mater. Interfaces 11 , 33458-33464 (2019). Cai, W. et al. Increasing ionic strength and valency of cations enhance sorption through hydrophobic interactions of PFAS with soil surfaces. Sci. Total Environ. 817 , 152975 (2022). Nguyen, T. M. H. et al. Influences of chemical properties, soil properties, and solution pH on soil–water partitioning coefficients of per-and polyfluoroalkyl substances (PFASs). Environ. Sci. Technol. 54 , 15883-15892 (2020). Rosenblum, L. & Wendelken, S. Method 533: determination of per-and polyfluoroalkyl substances in drinking water by isotope dilution anion exchange solid phase extraction and liquid chromatography/tandem mass spectrometry. Tandem Mass Spectrometry 52 (2019). Shoemaker, J. & Tettenhorst, D. Method 537.1: determination of selected per-and polyfluorinated alkyl substances in drinking water by solid phase extraction and liquid chromatography/tandem mass spectrometry (LC/MS/MS). National Center for Environmental Assessment, Washington, DC (2018). Shoemaker, J., Grimmett, P. & Boutin, B. Method 537. Determination of selected perfluorinated alkyl acids in drinking water by solid phase extraction and liquid chromatography/tandem mass spectrometry (LC/MS/MS). Tandem Mass Spectrometry (LC/MS/MS) (2009). Stuart, B. H. Polymer analysis . (John Wiley & Sons, 2008). Zhao, L. et al. Universal salt-assisted assembly of MXene from suspension on polymer substrates. Nat. Commun. 15 , 10027 (2024). Additional Declarations Yes there is potential Competing Interest. B.L., L.Z., W.X., and C.G. filed a U.S. Provisional Patent. The remaining authors declare no competing interests. Supplementary Files SI.docx Supplementary information Cite Share Download PDF Status: Under Review Version 1 posted 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. 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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-5861495","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":414335618,"identity":"ee42e98a-3870-4502-80b7-b3c08d5176d3","order_by":0,"name":"Bo Li","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA0ElEQVRIiWNgGAWjYBACAwYGxgMJFQw8fOxwsQSCWhgOJJxh4GFjJkkLYxsDA/FazNkbGA48nHdYho2Z+dmDj212DPzsOQZ4tVj2HGA4kLjtMNBhbOaGM9uSGSR73uDXYnAjAaQlDeQXM2meM8xAEQK2QLTMAWlh/wbUUs9gT5yWBhugFh6gLRWHGQwkCPrlYMOBhGNgLWWSMyqO80iceVaAV4s5e/PBhz9qJOz52du3SXwwqJbjb0/egFcLMPIbULg8BJSPglEwCkbBKCAGAADh9z1hsfJAjwAAAABJRU5ErkJggg==","orcid":"https://orcid.org/0000-0001-9766-7925","institution":"Villanova University","correspondingAuthor":true,"prefix":"","firstName":"Bo","middleName":"","lastName":"Li","suffix":""},{"id":414335619,"identity":"2f47a2cf-3ac5-4919-bae5-d49c2cb70802","order_by":1,"name":"Liang Zhao","email":"","orcid":"https://orcid.org/0000-0003-1567-6516","institution":"Villanova University","correspondingAuthor":false,"prefix":"","firstName":"Liang","middleName":"","lastName":"Zhao","suffix":""},{"id":414335620,"identity":"8c1caab5-68db-42ff-a048-d2ec4fc77c2a","order_by":2,"name":"Jiayue Hu","email":"","orcid":"","institution":"Temple University","correspondingAuthor":false,"prefix":"","firstName":"Jiayue","middleName":"","lastName":"Hu","suffix":""},{"id":414335621,"identity":"85098894-4fcb-44e1-9866-441e2e4d6cf8","order_by":3,"name":"Chenchi Gong","email":"","orcid":"","institution":"Villanova University","correspondingAuthor":false,"prefix":"","firstName":"Chenchi","middleName":"","lastName":"Gong","suffix":""},{"id":414335622,"identity":"72a3e341-1c9d-41fb-94c5-7885d74af234","order_by":4,"name":"Alexis Dyke","email":"","orcid":"","institution":"Villanova University","correspondingAuthor":false,"prefix":"","firstName":"Alexis","middleName":"","lastName":"Dyke","suffix":""},{"id":414335623,"identity":"05fb747c-ecc9-4b7f-aaca-ceefc4bca0cd","order_by":5,"name":"Han Cao","email":"","orcid":"https://orcid.org/0000-0002-9451-6926","institution":"Villanova University","correspondingAuthor":false,"prefix":"","firstName":"Han","middleName":"","lastName":"Cao","suffix":""},{"id":414335624,"identity":"0aac1466-7714-45cc-b394-6a7233c291f7","order_by":6,"name":"Jianlei Wu","email":"","orcid":"","institution":"Villanova University","correspondingAuthor":false,"prefix":"","firstName":"Jianlei","middleName":"","lastName":"Wu","suffix":""},{"id":414335625,"identity":"2b2afc88-6178-4437-96b4-698b79998bbd","order_by":7,"name":"Laura Bracaglia","email":"","orcid":"","institution":"Villanova University","correspondingAuthor":false,"prefix":"","firstName":"Laura","middleName":"","lastName":"Bracaglia","suffix":""},{"id":414335626,"identity":"27acaafd-2f17-47c3-af7b-be10289acc78","order_by":8,"name":"Ling Liu","email":"","orcid":"https://orcid.org/0000-0001-8743-4570","institution":"Temple University","correspondingAuthor":false,"prefix":"","firstName":"Ling","middleName":"","lastName":"Liu","suffix":""},{"id":414335627,"identity":"e3f17ef4-4009-4e3d-a727-947e90a958e4","order_by":9,"name":"Wenqing Xu","email":"","orcid":"","institution":"Villanova University","correspondingAuthor":false,"prefix":"","firstName":"Wenqing","middleName":"","lastName":"Xu","suffix":""}],"badges":[],"createdAt":"2025-01-19 22:35:19","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-5861495/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-5861495/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":76109770,"identity":"97cecaac-6dc9-4e52-8c32-03fd68e73417","added_by":"auto","created_at":"2025-02-12 11:50:05","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":247056,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eDesign principle of MPRS for PFAS detection.\u003c/strong\u003e \u003cstrong\u003ea\u003c/strong\u003e, Schematics of PFAS (e.g., PFOA) adsorption process on a PDMS substrate and Raman testing across the PFAS and PDMS interface. \u003cstrong\u003eb\u003c/strong\u003e, Raman spectra of PDMS and PFOA@PDMS. The inset is the enlarged spectra at around 2902.8 cm\u003csup\u003e-1\u003c/sup\u003e. \u003cstrong\u003ec\u003c/strong\u003e, ToF-SIMS mapping of F\u003csup\u003e- \u003c/sup\u003eof PFOA@PDMS. Scale bar, 50 μm. \u003cstrong\u003ed\u003c/strong\u003e, Integrated ToF-SIMS spectra of PFOA@PDMS and PDMS.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-5861495/v1/faeeb42d03109af0c9fe265f.png"},{"id":76109772,"identity":"aba5ccc8-b265-4532-98f0-11704edc980c","added_by":"auto","created_at":"2025-02-12 11:50:05","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":114622,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eQuantitative control of PFAS detection. a\u003c/strong\u003e, Detection of PFOA at concentrations ranging from 2.8 × 10\u003csup\u003e-1\u003c/sup\u003e to 2.8 × 10\u003csup\u003e-21\u003c/sup\u003e g/L with \u003cem\u003et\u003c/em\u003e\u003csub\u003eadsorption\u003c/sub\u003e of 2 min and 10 min. \u003cstrong\u003eb\u003c/strong\u003e, Adsorption time-dependent detection of PFOA with a fixed concentration of 2.8 ×10\u003csup\u003e-9\u003c/sup\u003e\u003cstrong\u003e \u003c/strong\u003eg/L. \u003cstrong\u003ec\u003c/strong\u003e, Comparison of MPRS detection for different PFAS at 2.8 ×10\u003csup\u003e-9\u003c/sup\u003e\u003cstrong\u003e \u003c/strong\u003eg/L with a \u003cem\u003et\u003c/em\u003e\u003csub\u003eadsorption\u003c/sub\u003e of 10 min. \u003cstrong\u003ed\u003c/strong\u003e, Comparison of processing time and PFAS LOD between MPRS and methods collected from literature. For processing time, we use concentrating time for HPLC-MS/MS (and LC-MS), and \u003cem\u003et\u003c/em\u003e\u003csub\u003eadsorption\u003c/sub\u003e for all other methods including MPRS.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-5861495/v1/4196a5f2898496c9c167029f.png"},{"id":76109775,"identity":"3bc24425-13ea-4ab7-8e02-19518d91fb2b","added_by":"auto","created_at":"2025-02-12 11:50:06","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":260812,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eMolecular dynamics simulation and density functional theory of PFOA detection. a\u003c/strong\u003e,\u003cstrong\u003e \u003c/strong\u003eIllustration of MD model and PFOA molecules adsorption process on PDMS substrate (grey, C; green, F; red, O; white, H; blue, Si). Water molecules are omitted for clarity. A z-axis is defined starting from the surface of PDMS substrate. \u003cstrong\u003eb\u003c/strong\u003e, Atomic distribution profiles of F and O in PFOA, C in PDMS, and water as a function of z from the MD simulations. The C distribution is also plotted as a gradient background to visualize the interface, showing that PDMS and water lack a clear boundary. The PDMS surface (\u003cem\u003ez\u003c/em\u003e = 0) is defined where the molar density of C is half of its original value. \u003cstrong\u003ec\u003c/strong\u003e, System potential energy variations during the PFOA adsorption process in pure water. Pale cyan dots represent raw energy data from MD simulations. Solid curve represents the averaged energy in each location, and the shade region represents the energy standard deviation. \u003cstrong\u003ed\u003c/strong\u003e, Optimized configurations of PFOA and PDMS molecules after adsorption in DFT. The iso-surfaces show charge density difference profiles between -CH\u003csub\u003e3\u003c/sub\u003e of PDMS and -CF\u003csub\u003e3\u003c/sub\u003e of PFOA (cyan: charge accumulation, red: charge depletion). Iso-surfaces refers to a level of 0.0005 Bohr\u003csup\u003e-3\u003c/sup\u003e. \u003cstrong\u003ee\u003c/strong\u003e, Charge density distributions on C-H bonds of PDMS -CH\u003csub\u003e3\u003c/sub\u003e group near PFOA. \u003cstrong\u003ef\u003c/strong\u003e, Density of states (DOS) of PDMS, where curves show total DOS of PDMS (top), partial DOS of PDMS before (middle) and after (bottom) PFOA adsorption. The Fermi level is positioned at 0 eV. The conduction bands in partial DOS plots are amplified for clarity in insets.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-5861495/v1/c5eff6297f82f69dd74ccc34.png"},{"id":76109774,"identity":"79e3f67b-5e54-4b05-ba33-1da91e7df781","added_by":"auto","created_at":"2025-02-12 11:50:05","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":367845,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eDetection of PFOA by MPRS in complex environmental and human samples.\u003c/strong\u003e \u003cstrong\u003ea\u003c/strong\u003e, Schematic illustration of PFOA polluted water sources and on-site detection scenario. \u003cstrong\u003eb\u003c/strong\u003e, Effect of salt concentration on the \u003cem\u003eR\u003c/em\u003e\u003csub\u003eE\u003c/sub\u003e values in PFOA-spiked aqueous solution (\u003cem\u003et\u003c/em\u003e\u003csub\u003eadsoprtion\u003c/sub\u003e = 2 min). \u003cstrong\u003ec\u003c/strong\u003e, PFOA detection by MPRS in PFOA-spiked surface water (\u003cem\u003et\u003c/em\u003e\u003csub\u003eadsoprtion\u003c/sub\u003e = 2 min). \u003cstrong\u003ed\u003c/strong\u003e, PFOA detection by MPRS in PFOA-spiked human blood (\u003cem\u003et\u003c/em\u003e\u003csub\u003eadsoprtion\u003c/sub\u003e = 2 min). \u003cstrong\u003ee\u003c/strong\u003e, MPRS test of PFOA-spiked aqueous solution using a portable Raman spectrometer (\u003cem\u003et\u003c/em\u003e\u003csub\u003eadsoprtion\u003c/sub\u003e = 2 min).\u0026nbsp;\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-5861495/v1/b18f543d34126f41969a867e.png"},{"id":79047072,"identity":"39327434-93d1-4a40-bb1d-29d0c68b3344","added_by":"auto","created_at":"2025-03-23 15:03:20","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1696801,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5861495/v1/8319f5a5-829a-4cff-87e9-340f23ff3b22.pdf"},{"id":76109789,"identity":"3db65fab-c942-4a8f-ad21-ad0a6219d1bb","added_by":"auto","created_at":"2025-02-12 11:50:07","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":62218840,"visible":true,"origin":"","legend":"Supplementary information","description":"","filename":"SI.docx","url":"https://assets-eu.researchsquare.com/files/rs-5861495/v1/1291c6060b39b7a3b302cdea.docx"}],"financialInterests":"\u003cb\u003eYes\u003c/b\u003e there is potential Competing Interest.\nB.L., L.Z., W.X., and C.G. filed a U.S. Provisional Patent. The remaining authors declare no competing interests.","formattedTitle":"Molecule-Probed Raman Spectroscopy for Femtogram-per-Liter Level Per- and Polyfluoroalkyl Substances Detection","fulltext":[{"header":"Main","content":"\u003cp\u003ePer- and polyfluoroalkyl substances (PFAS) are a family of synthetic organo-fluoride compounds that have been extensively utilized in various industrial and consumer applications\u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e. Characterized by their strong carbon-fluorine bonds, PFAS are resistant to environmental degradation\u003csup\u003e\u003cspan additionalcitationids=\"CR3 CR4\" citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u003c/sup\u003e and can accumulate in biological systems\u003csup\u003e\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e,\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u003c/sup\u003e, which raises significant concerns over their adverse effects on human health and ecological systems. Notably, exposure to PFAS from both manufacturing and inappropriate waste disposal practices has been linked to various health risks, such as cancers and pregnancy-induced hypertension\u003csup\u003e\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e,\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u003c/sup\u003e. As of April 2024, the United States Environmental Protection Agency (EPA) established enforceable Maximum Contaminant Levels (MCLs) for six PFAS compounds in drinking water. For instance, the individual MCL is 4 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;9\u003c/sup\u003e g/L for the legacy PFAS compounds, perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS)\u003csup\u003e\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u003c/sup\u003e. However, PFAS levels of 4 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;9\u003c/sup\u003e g/L in drinking water will likely lead to lower levels present in blood and biological tissues\u003csup\u003e\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u003c/sup\u003e. Moreover, with a progressive understanding of the impact of accumulated trace-amount PFAS, the MCL could be further tightened. Therefore, it is critical to develop analytical methods with lower detection limits than the current MCL for currently available methods.\u003c/p\u003e \u003cp\u003eThe current gold standard for PFAS detection is liquid chromatography with tandem mass spectrometry (LC-MS/MS), which requires expensive instrumentation, specialized operator training, time-consuming and labor-intensive sample processing, and is cost-prohibitive for large-scale monitoring (e.g., hundreds of dollars per sample)\u003csup\u003e\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e. Significant efforts have been made to develop affordable detection methods with a target of highly sensitive and fast detection of PFAS. These methods monitor the changes in optical\u003csup\u003e\u003cspan additionalcitationids=\"CR14 CR15 CR16 CR17\" citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u003c/sup\u003e, electrical\u003csup\u003e\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e, thermal\u003csup\u003e\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u003c/sup\u003e, electrochemical signals\u003csup\u003e\u003cspan additionalcitationids=\"CR22 CR23 CR24 CR25\" citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u003c/sup\u003e of a substrate upon interaction with PFAS molecules. For example, a limit of detection (LOD) of 2 \u0026times; 10\u003csup\u003e\u0026ndash;12\u003c/sup\u003e g/L was achieved by an impedance-based electrochemical method leveraging the two-dimensional conductive metal-organic framework (MOF) with high-density metal sites for PFOA adsorption \u003csup\u003e\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u003c/sup\u003e. However, these methods are facing challenges such as limited sensitivity\u003csup\u003e\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u003c/sup\u003e, difficulty to scale up\u003csup\u003e\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e\u003c/sup\u003e, and false positivity from other substances (e.g., ions) in complex environments\u003csup\u003e\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eRaman spectroscopy captures the vibration modes of PFAS molecules, which has received immense attention for PFAS detection due to its simplicity and ease of operation\u003csup\u003e\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e\u003c/sup\u003e. A notable example is Surface-Enhanced Raman Spectroscopy (SERS), which utilizes enhanced local electromagnetic fields between noble metal nanoparticles on the substrate to amplify the Raman signals of captured PFAS molecules. However, to our best knowledge, the LODs of the SERS for PFOA detection range from 10\u003csup\u003e\u0026ndash;10\u003c/sup\u003e to 10\u003csup\u003e\u0026minus;\u0026thinsp;5\u003c/sup\u003e g/L\u003csup\u003e31\u0026ndash;34\u003c/sup\u003e. Moreover, the fluorescence background of PFAS has been observed (e.g., at a PFOA concentration of 0.1 g/L) to interfere with their Raman signals\u003csup\u003e\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e\u003c/sup\u003e. In addition, the price of noble metal nanoparticles and their sophisticated manufacturing process for size and spatial distribution control elevate the cost and increase the overall processing time.\u003c/p\u003e \u003cp\u003eThis study reports on a new PFAS detection mechanism, Molecule-Probed Raman Spectroscopy (MPRS). This mechanism represents a paradigm shift in Raman Spectroscopy, moving from detecting the fingerprint spectrum of the analyte to monitoring the spectrum change of molecular probes (MPs) on a substrate upon analyte capture. The baseline signal of MPRS is strong and stable as MPs are abundant and uniformly distributed on the surface of a substrate. Upon capturing PFAS, we observed an enhancement in the Raman intensity of MPs, e.g., symmetric vibration at 2902.8 cm\u003csup\u003e-\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e of -CH\u003csub\u003e3\u003c/sub\u003e groups on a polydimethylsiloxane (PDMS) substrate. Accordingly, we achieved femtogram-per-liter level detection of perfluorooctanoic acid (i.e., 3.7 \u0026times; 10\u003csup\u003e\u0026ndash;15\u003c/sup\u003e g/L), surpassing the limit of detection (LOD) of SERS for PFOA detection by at least five orders of magnitude (e.g., 10\u003csup\u003e\u0026ndash;10\u003c/sup\u003e to 10\u003csup\u003e\u0026minus;\u0026thinsp;5\u003c/sup\u003e g/L)\u003csup\u003e31\u0026ndash;34\u003c/sup\u003e and the LOD of the gold standard, liquid chromatography with tandem mass spectrometry (LC-MS/MS) by four orders of magnitude\u003csup\u003e\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e. It is important to note ultrasensitive detection of PFAS is only one example of the application of MPRS, the new mechanism will open the gate toward unlimited combinations of MPs and analytes in water and will promote new instrumentation developments in Raman spectroscopy.\u003c/p\u003e\n\u003ch3\u003ePrinciple of MPRS and PFOA detection\u003c/h3\u003e\n\u003cp\u003eThe MPRS design is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea. Methyl groups (-CH\u003csub\u003e3\u003c/sub\u003e) on the surface of a PDMS substrate function as the molecular probe. Fluorine (F) atoms in PFAS are connected to the carbon chain through covalent bonds and impart strong electronegativity\u003csup\u003e\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e\u003c/sup\u003e. When PFAS molecules approach -CH\u003csub\u003e3\u003c/sub\u003e groups on the surface of PDMS, fluorine can polarize the C-H bond in methyl groups, increasing the Raman intensity of its methyl groups. In this study, PDMS is spin-coated on a SiO₂/Si wafer to achieve a molecularly flat surface (roughness (\u003cem\u003eR\u003c/em\u003e\u003csub\u003eq\u003c/sub\u003e)\u0026thinsp;=\u0026thinsp;0.2 nm, Supplementary Fig. \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e). Confocal Raman microscope (CRM) is used to focus on the surface of PDMS and capture the changes in PDMS spectrum upon PFAS adsorption. To ensure uniform adsorption of PFAS on the surface of PDMS, we utilized a combined dipping (average speed\u0026thinsp;=\u0026thinsp;1.5 m/min) and sonication (40 kHz and 60 W) process for 10 min (\u003cem\u003et\u003c/em\u003e\u003csub\u003eadsorption\u003c/sub\u003e = 10 min). The substrate was submerged in the solution during the entire PFAS adsorption process. The dipping creates a shear field to facilitate a uniform deposition of PFAS, while the sonication in PFAS solution not only helps to maintain well-dispersed PFAS molecules but also energizes PFAS to achieve fast deposition\u003csup\u003e\u003cspan additionalcitationids=\"CR38\" citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e\u003c/sup\u003e. As a proof of concept, we first chose perfluorooctanoic acid (PFOA) dissolved in deionized (DI) water with a concentration (\u003cem\u003eC\u003c/em\u003e\u003csub\u003ePFOA\u003c/sub\u003e) of 2.8 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;9\u003c/sup\u003e g/L. The PDMS substrate with adsorbed PFOA (PFOA@PDMS) was rinsed with DI water and dried under nitrogen. CRM measurement conditions are fixed unless mentioned otherwise (i.e., \u0026times;50 lens, 532 nm wavelength for laser excitation, 3 mW for laser power, 10 seconds for integration time, and accumulation time of 1). Figure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb compares the Raman spectra of PDMS and PFOA@PDMS. While most of the characteristic peaks of PDMS remain overlapping, the peak intensity (\u003cem\u003eI\u003c/em\u003e) of symmetric stretching vibration of methyl groups (\u003cem\u003eν\u003c/em\u003e\u003csub\u003es\u003c/sub\u003e (-CH\u003csub\u003e3\u003c/sub\u003e), 2902.8 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) increases by 280 counts compared to its intensity of pristine PDMS (\u003cem\u003eI\u003c/em\u003e\u003csub\u003e0\u003c/sub\u003e) with a Raman intensity enhancement (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{R}_{\\text{E}}=(I-{I}_{0})/{I}_{0}\\)\u003c/span\u003e\u003c/span\u003e) of 5.9%. Even for a shorter adsorption time (\u003cem\u003et\u003c/em\u003e\u003csub\u003eadsorption\u003c/sub\u003e = 2 min), we can still achieve a \u003cem\u003eR\u003c/em\u003e\u003csub\u003eE\u003c/sub\u003e of 1.6% (Supplementary Fig. S2a). It is interesting to know that \u003cem\u003eR\u003c/em\u003e\u003csub\u003eE\u003c/sub\u003e has not shown notable changes within a wide range of laser power (e.g., 1 to 5 mW), demonstrating the excellent stability and tolerance of MPRS against changing measurement conditions (Supplementary Fig. S3). Both \u003cem\u003eR\u003c/em\u003e\u003csub\u003eE\u003c/sub\u003e values at \u003cem\u003et\u003c/em\u003e\u003csub\u003eadsorption\u003c/sub\u003e = 2 min and 10 min are significantly larger than the instrument noise (0.5%), determined by monitoring the \u003cem\u003eν\u003c/em\u003e\u003csub\u003es\u003c/sub\u003e (-CH\u003csub\u003e3\u003c/sub\u003e) stretching peak at 2902.8 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e for 200 detecting cycles with an interval of 2 seconds between cycles (Supplementary Fig. S4).\u003c/p\u003e \u003cp\u003eTo verify that the signal enhancement was truly due to the adsorption of PFOA, time-of-flight secondary ion mass spectrometry (ToF-SIMS) was performed. The results demonstrate a uniform distribution of F element by capturing the ionized state of PFOA (i.e., F\u003csup\u003e\u0026minus;\u003c/sup\u003e) (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec and \u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ed, Supplementary Fig. S2b, Supplementary Fig. S2c, and Supplementary Fig. S5). It should be noted that a slight increase (\u003cem\u003eR\u003c/em\u003e\u003csub\u003eE\u003c/sub\u003e = 1.1%) of asymmetric methyl groups (\u003cem\u003eν\u003c/em\u003e\u003csub\u003eas\u003c/sub\u003e (-CH\u003csub\u003e3\u003c/sub\u003e), 2964.4 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) can be found, suggesting a similar fluorine-induced polarization mechanism may be applied to other vibration modes (Supplementary Fig. S6). Here, we focus on \u003cem\u003eν\u003c/em\u003e\u003csub\u003es\u003c/sub\u003e (-CH\u003csub\u003e3\u003c/sub\u003e) stretching at 2902.8 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e due to its larger signal-to-noise ratio to clarify the effectiveness and mechanism of MPRS.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003ePFAS detection capabilities of MPRS\u003c/h2\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e elucidates the detection capabilities of MPRS. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea, the influence of PFOA concentration on the \u003cem\u003eR\u003c/em\u003e\u003csub\u003eE\u003c/sub\u003e was illustrated at two adsorption times (i.e., \u003cem\u003et\u003c/em\u003e\u003csub\u003eadsorption\u003c/sub\u003e = 10 min and 2 min). Controls with PFOA (i.e., 2.8 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;7\u003c/sup\u003e g/L) or without PFOA in DI water were measured by MPRS and validated using LC-MS/MS (Supplementary Table \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e). For \u003cem\u003et\u003c/em\u003e\u003csub\u003eadsorption\u003c/sub\u003e = 10 min (square), a linear relationship between \u003cem\u003eR\u003c/em\u003e\u003csub\u003eE\u003c/sub\u003e and logarithmic PFOA concentrations (i.e., 2.8 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e to 2.8 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;17\u003c/sup\u003e g/L) was observed down to 2.8 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;17\u003c/sup\u003e g/L and then the curve reaches a plateau. A similar plateau is reached for the curve with \u003cem\u003et\u003c/em\u003e\u003csub\u003eadsorption\u003c/sub\u003e = 2 min (circle) when the concentration reaches 2.8 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;13\u003c/sup\u003e g/L and lower. This plateau matches the Raman enhancement (\u003cem\u003eR\u003c/em\u003e\u003csub\u003eE\u003c/sub\u003e = 0.6%) of PDMS dipped in pure DI water, which is considered the blank sample. Therefore, we defined \u003cem\u003eR\u003c/em\u003e\u003csub\u003eE\u003c/sub\u003e = 0.6% as the water background (Supplementary Fig. S7). The LOD of MPRS can be determined using the concentration corresponding to three-fold water background (blank) in the linear fitting curve. Specifically, a LOD of 3.7 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;15\u003c/sup\u003e g/L for PFOA can be achieved for \u003cem\u003et\u003c/em\u003e\u003csub\u003eadsorption\u003c/sub\u003e = 10 min, which is 6 orders of magnitude lower than the current MCL (i.e., 4 \u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;9\u003c/sup\u003e g/L)\u003csup\u003e10\u003c/sup\u003e. For a fast detection with \u003cem\u003et\u003c/em\u003e\u003csub\u003eadsorption\u003c/sub\u003e = 2 min, we can still achieve a LOD of 4.3 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;9\u003c/sup\u003e g/L for PFOA. The comparison of the two curves shows that longer adsorption time leads to higher \u003cem\u003eR\u003c/em\u003e\u003csub\u003eE\u003c/sub\u003e at the same concentration. If \u003cem\u003eR\u003c/em\u003e\u003csub\u003eE\u003c/sub\u003e only originates from the interfacial interaction between -CH\u003csub\u003e3\u003c/sub\u003e on PDMS and -CF\u003csub\u003e2\u003c/sub\u003e/-CF\u003csub\u003e3\u003c/sub\u003e on PFOA, a plateau should be reached when the surface of PDMS is fully covered with PFAS. To validate this hypothesis, we increased the adsorption time (1 min to 30 min) at a fixed concentration (e.g., \u003cem\u003eC\u003c/em\u003e\u003csub\u003ePFOA\u003c/sub\u003e = 2.8 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;9\u003c/sup\u003e g/L). We found the peak intensity reaches a plateau at \u003cem\u003et\u003c/em\u003e\u003csub\u003eadsorption\u003c/sub\u003e = 20 min as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb. Further adsorption of PFAS on top of the existing PFAS layer could not polarize the molecular probes on PDMS due to the increased distance.\u003c/p\u003e \u003cp\u003eTo further explore MPRS detection capabilities, we investigated the response of four additional PFAS: perfluorobutanoic acid (PFBA), perfluorooctane sulfonates (PFOS), perfluorobutane sulfonate (PFBS), and hexafluoropropylene oxide dimer acid (GenX), at a concentration of 2.8 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;9\u003c/sup\u003e g/L (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec). According to the ToF-SIMS results presented in Supplementary Fig. S8, we first confirmed the uniform deposition of each PFAS onto the PDMS surface after 10 min adsorption. Although all PFAS can induce the Raman enhancement of \u003cem\u003eν\u003c/em\u003e\u003csub\u003es\u003c/sub\u003e (-CH\u003csub\u003e3\u003c/sub\u003e) peak at 2902.8 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, the magnitudes of \u003cem\u003eR\u003c/em\u003e\u003csub\u003eE\u003c/sub\u003e vary with different chain lengths and head groups. The PFAS with the same carbon chain length shows similar \u003cem\u003eR\u003c/em\u003e\u003csub\u003eE\u003c/sub\u003e (e.g., PFOA (5.9%) and PFOS (6.8%)), whereas the \u003cem\u003eR\u003c/em\u003e\u003csub\u003eE\u003c/sub\u003e of PFBA and PFBS are much smaller (e.g., PFBA (2.7%) and PFBS (2.6%)). The decrease in \u003cem\u003eR\u003c/em\u003e\u003csub\u003eE\u003c/sub\u003e values can be explained by the lower partition coefficients (\u003cem\u003eK\u003c/em\u003e\u003csub\u003e\u003cem\u003eD\u003c/em\u003e\u003c/sub\u003e) of shorter-chain PFAS than longer-chain PFAS, which increases the hydrophilicity\u003csup\u003e\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e,\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e\u003c/sup\u003e. The \u003cem\u003eR\u003c/em\u003e\u003csub\u003eE\u003c/sub\u003e of GenX is smaller than those of PFOA and PFOS which can be attributed to the increased hydrophilicity from a shorter carbon chain and additional oxygen atoms in the backbone.\u003c/p\u003e \u003cp\u003eThe advantage of MRPS is elaborated in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed and Supplementary Table S2, where the processing time and LOD among different PFOA detection methods are compared. It is important to note processing procedures vary drastically for different methods. However, the overall processing time should include the sample preparation time and detection time. For MPRS, the sample preparation includes substrate preparation (e.g., 1 min for spin coating PDMS\u0026thinsp;+\u0026thinsp;5 min for PDMS curing) and PFAS adsorption (e.g., \u003cem\u003et\u003c/em\u003e\u003csub\u003eadsorption\u003c/sub\u003e = 2\u0026ndash;10 min). The detection time of the Raman spectrum is 1\u0026ndash;5 min depending on how many sampling points are surveyed. By contrast, the LC-MS/MS method (e.g., Methods 533, 537, and 537.1) has more than five sample preparation procedures, which take hours to days according to the equipment manual\u003csup\u003e\u003cspan additionalcitationids=\"CR43\" citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e\u003c/sup\u003e. Unfortunately, since there is no standard to document the time for each procedure, to simplify the comparison in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed, the processing time for LC-MS/MS is set to be 24 hours and for all other methods, PFAS adsorption time (\u003cem\u003et\u003c/em\u003e\u003csub\u003eadsorption\u003c/sub\u003e) is used to compare the processing time. Similar to processing time, the definition of LOD varies with different methods as summarized in Supplementary Table S2. Still, the comparison suggests the LOD of MPRS is far superior to existing methods. It is 3 orders of magnitude lower than the state-of-the-art results from LC-MS/MS (and LC/MS/MS) with a processing time of at least 2 orders of magnitude shorter. Compared to SERS, MPRS is 5 orders of magnitude more sensitive. Moreover, MPRS can be more affordable than SERS as the substrate of MPRS is made of commercial polymer, whereas SERS requires a sophisticated and time-consuming metal deposition process.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eDetection mechanism\u003c/h3\u003e\n\u003cp\u003eThe PFAS detection mechanism is revealed through a combination of classical molecular dynamics (MD) simulations and quantum ab-initio calculations using PFOA as an example. MD simulations analyze the adsorption process and energetics, providing molecular configurations for ab-initio calculations, which then explore the change of electronic structures in the -CH\u003csub\u003e3\u003c/sub\u003e group of PDMS as PFOA approaches. Figure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eA illustrates the adsorption process of 50 PFOA molecules onto a PDMS substrate in water. The detailed parameter set-up can be found in Supplementary Table S3. The center of mass (COM) of the PFOA molecular cluster is initially positioned at \u003cem\u003ez\u003c/em\u003e\u0026thinsp;=\u0026thinsp;20.00 \u0026Aring; above the PDMS surface (see Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb for the definition of the surface). Due to the hydrophobic nature of the difluoromethyl (-CF\u003csub\u003e2\u003c/sub\u003e) and trifluoromethyl (-CF\u003csub\u003e3\u003c/sub\u003e) groups, neighboring PFOA molecules coalesce into clusters and move towards the hydrophobic PDMS surface. After 20 ns, the system reaches equilibrium, with the PFOA molecules dispersing across the PDMS surface and the COM settling at \u003cem\u003ez\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.97\u0026thinsp;\u0026plusmn;\u0026thinsp;0.23 \u0026Aring;.\u003c/p\u003e \u003cp\u003eMolecular trajectories indicate that PFOA molecules tend to align parallel to the PDMS surface (Supplementary Fig. S9). In this configuration, the -CF\u003csub\u003e2\u003c/sub\u003e and -CF\u003csub\u003e3\u003c/sub\u003e groups of PFOA are strongly attracted to the methyl (-CH\u003csub\u003e3\u003c/sub\u003e) groups of PDMS, while the head groups (i.e., -COOH) of PFOA orient away from the hydrophobic substrate (see Supplementary Fig. S10 for three examples of the molecular configuration). Indeed, a molar density plot (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb) reveals that F has a peak density of 38.83 mol/L at \u003cem\u003ez\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.76 \u0026Aring;, very close to PDMS, while O peaks at 3.65 mol/L at \u003cem\u003ez\u003c/em\u003e\u0026thinsp;=\u0026thinsp;3.36 \u0026Aring; indicating a greater distance. The close methyl-fluorocarbon interaction strongly governs the adsorption and detection of PFOA. As depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec, the system\u0026rsquo;s potential energy decreases as PFOA approaches the PDMS substrate, confirming a thermodynamically favorable adsorption process. Notably, PFOA molecules are ionized in the aqueous environment. Our MD simulations show that ionic and neutral PFOA exhibit similar adsorption processes and results (Supplementary Fig. S11).\u003c/p\u003e \u003cp\u003eThe PFOA detection mechanism is further explored through quantum ab-initio calculations. Figure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed illustrates the local charge density difference near the -CH\u003csub\u003e3\u003c/sub\u003e group of PDMS before and after PFOA adsorption. The iso-surfaces represent a charge density difference level of 0.0005 Bohr\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e. Since F atoms have a significantly higher electronegativity than H atoms, electrons associated with the -CH\u003csub\u003e3\u003c/sub\u003e group of PDMS and the -CF\u003csub\u003e3\u003c/sub\u003e group of PFOA tend to shift closer to the F atoms. An electron accumulation region then forms near the F atoms in the -CF\u003csub\u003e3\u003c/sub\u003e group, while an electron depletion region appears between the -CH\u003csub\u003e3\u003c/sub\u003e and -CF\u003csub\u003e3\u003c/sub\u003e groups. This redistribution of electrons alters the electronic structure in the C-H bond, causing local polarization of charge density within the -CH\u003csub\u003e3\u003c/sub\u003e group. Multiple optimized adsorption configurations were examined, all yielding consistent results (Supplementary Fig. S12).\u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ee presents a planar charge density color map that quantitatively reveals changes in the electronic structure of -CH\u003csub\u003e3\u003c/sub\u003e as it serves as a molecular probe for PFAS detection. The charge density map is plotted in a plane formed by two bonds, C-H1 and C-H2, as illustrated in the inset of Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ee. The C-H1 bond is strongly attracted by and the closest to the -CF\u003csub\u003e3\u003c/sub\u003e group, while the other two bonds (C-H2 and C-H3) are less affected. Due to the strong interaction with PFOA, the C-H1 bond develops a dumbbell-shaped charge density profile, showing significant changes compared to its state before PFOA adsorption (Supplementary Fig. S13). In contrast, the charge density near the C-H2 bond remains largely unchanged. These results demonstrate that the approaching C-F bonds in PFOA redistribute electrons in the -CH\u003csub\u003e3\u003c/sub\u003e groups of PDMS, particularly along the C-H bond closest to PFOA.\u003c/p\u003e \u003cp\u003eThe density of states (DOS) was further calculated to investigate how PFOA adsorption affects the electronic structure of the -CH\u003csub\u003e3\u003c/sub\u003e group in PDMS. Total and partial DOS curves for PDMS are presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ef. The bandgap of pristine PDMS was found to be 4.89 eV, consistent with its insulating nature. According to the total DOS, after PFOA adsorption, small peaks appear below the bottom of the conduction band (CB), and the top edge of CB decreases. Partial DOS is further analyzed to pinpoint the influence on each atom in the -CH\u003csub\u003e3\u003c/sub\u003e group. In the valence band (VB), the C \u003cem\u003e2p\u003c/em\u003e orbitals are prevalent in the upper portion of the VB, whereas both H \u003cem\u003e1s\u003c/em\u003e and C \u003cem\u003e2p\u003c/em\u003e orbitals contribute to the lower portion of the VB, indicating strong covalence connection between the C and H atoms. After PFOA adsorption, PFOA alters the distribution of H \u003cem\u003e1s\u003c/em\u003e and C \u003cem\u003e2p\u003c/em\u003e states between \u0026minus;\u0026thinsp;4.69 eV and \u0026minus;\u0026thinsp;1.26 eV; and both H \u003cem\u003e1s\u003c/em\u003e and C \u003cem\u003e2p\u003c/em\u003e orbitals tend to occupy higher energy levels. In the CB, the C \u003cem\u003e2p\u003c/em\u003e orbitals are prevalent. After PFOA adsorption, the CB is shortened from 4.99 eV to 3.45 eV, while the bottom edge of CB remains unchanged. The changes in DOS and charge density distribution account for the distinct features of -CH\u003csub\u003e3\u003c/sub\u003e groups in the Raman scattering spectra before and after PFOA adsorption\u003csup\u003e\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e\n\u003ch3\u003ePFOA detection in real scenarios\u003c/h3\u003e\n\u003cp\u003eIn real scenarios, PFAS detection faces challenges such as false positive signals from non-PFAS species and the requirement of on-site data collection in real-time (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea). We first examined the PFAS selectivity of MPRS against ions, which are common compositions of environmental water samples and human biological samples. The \u003cem\u003eR\u003c/em\u003e\u003csub\u003eE\u003c/sub\u003e of salt/DI water solutions at 1 mM with various salts (0.6% for CaCl\u003csub\u003e2\u003c/sub\u003e to 0.8% for Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e) without PFOA is comparable to the water background (0.6%), suggesting limited interactions between ions and molecular probes (-CH\u003csub\u003e3\u003c/sub\u003e) (Supplementary Table S4). On the other hand, adding salts (e.g., NaCl) to a PFOA-spiked DI water solution may show the difference. Figure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb shows the \u003cem\u003eR\u003c/em\u003e\u003csub\u003eE\u003c/sub\u003e evolution obtained in a PFOA-spiked aqueous solution with different NaCl salt concentrations (\u003cem\u003eC\u003c/em\u003e\u003csub\u003eNaCl\u003c/sub\u003e). In all tested salt/DI water systems, \u003cem\u003eR\u003c/em\u003e\u003csub\u003eE\u003c/sub\u003e values follow linear regression (versus logarithmic \u003cem\u003eC\u003c/em\u003e\u003csub\u003ePFOA\u003c/sub\u003e). Adding 1 mM NaCl into a PFOA-spiked aqueous solution does not significantly change the linear regression slope compared to the case without NaCl. But higher NaCl concentrations (10 mM to 1000 mM) lead to higher slopes. Further analysis (Supplementary Fig. S14) shows a linear regression between slope and \u003cem\u003eC\u003c/em\u003e\u003csub\u003eNaCl\u003c/sub\u003e (in logarithmic scale), demonstrating that NaCl salt can increase the adsorption efficiency of PFOA on PDMS. A similar phenomenon can be found in other salt-PFOA or mixed salt-PFOA systems (Supplementary Fig. S15). As a result, we can conclude that salts alone in aqueous solution (without PFOA) will not create a false positive signal. Instead, salts favorably enhance the interaction between PFOA and PDMS through a salting-out effect and increase the PFAS adsorption rate\u003csup\u003e\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e,\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e\u003c/sup\u003e, thereby increasing the \u003cem\u003eR\u003c/em\u003e\u003csub\u003eE\u003c/sub\u003e. Also, the linear relationship of both \u003cem\u003eR\u003c/em\u003e\u003csub\u003eE\u003c/sub\u003e-logarithmic \u003cem\u003eC\u003c/em\u003e\u003csub\u003ePFOA\u003c/sub\u003e and slope-logarithmic \u003cem\u003eC\u003c/em\u003e\u003csub\u003eNaCl\u003c/sub\u003e curves suggest the influence of salt can be predicted and calibrated.\u003c/p\u003e \u003cp\u003eWe further evaluated the MPRS performance in surface water (SW) and human blood spiked with different PFOA concentrations (the detailed processing information and real sample images can be found in Methods and Supplementary Fig. S16). These two systems are enriched with different ions and other possible contaminants. We first examined a possible \u003cem\u003eR\u003c/em\u003e\u003csub\u003eE\u003c/sub\u003e value in SW solution without spiking PFOA. The result displays a \u003cem\u003eR\u003c/em\u003e\u003csub\u003eE\u003c/sub\u003e (0.6\u0026thinsp;\u0026plusmn;\u0026thinsp;1.4%, Supplementary Fig. S17) similar to the water background (Supplementary Fig. S6) suggesting no detectable PFAS in SW. Moving forward, we spiked different concentrations of PFOA into SW. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ec, we obtained a linear correlation (slope\u0026thinsp;=\u0026thinsp;0.31, r\u003csup\u003e2\u003c/sup\u003e\u0026thinsp;=\u0026thinsp;0.96) of \u003cem\u003eR\u003c/em\u003e\u003csub\u003eE\u003c/sub\u003e with increasing PFOA concentrations. The cation, anion, and other component concentrations in SW were summarized in Supplementary Table S5-S8. This slope is higher than the case in the PFOA/DI water system (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea), further elaborating that salts in SW can enhance the adsorption of PFOA on PDMS. Compared to SW, human blood is a combination of water, proteins, salts (especially Fe cations), and cells. PFOA-spiked human blood samples from 3 volunteers were examined. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ed, two PFOA concentrations (2.8 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;9\u003c/sup\u003e and 2.8 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e g/L) were tested and \u003cem\u003eR\u003c/em\u003e\u003csub\u003eE\u003c/sub\u003e values are significantly higher than the instrument noise (0.5%) and its corresponding pure blood backgrounds for blood samples from all three volunteers.\u003c/p\u003e \u003cp\u003eFurthermore, we validate the potential of on-site PFAS detection using portable Raman (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ee). Here, the laser power is increased to 50 mW and \u003cem\u003et\u003c/em\u003e\u003csub\u003eadsorption\u003c/sub\u003e is 2 min. A linear enhancement curve can be obtained from PFOA-spiked aqueous solutions with a concentration range from 2.8 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;12\u003c/sup\u003e g/L to 2.8 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;6\u003c/sup\u003e g/L. Compared with CRM, portable Raman can focus on the surface, but the signal of some PDMS molecules underneath the surface (not in direct contact with PFOA molecules) will be collected. However, the enhanced signal is still strong enough to differentiate the concentration of PFOA.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"Conclusions","content":"\u003cp\u003eMPRS represents an affordable Raman detection strategy for ultrasensitive and fast detection of PFAS that meets a critical need for protecting the environment and human health as well as for implementing environmental regulation. MPRS can detect the concentration of a solution with a single known PFAS species as well as in complex systems such as surface water and blood. It should be noted that selectivity remains a challenge for MPRS when differentiating PFAS species in a multi-PFAS mixed solution. The discovery of new MPs targeting the head groups of PFAS could be a potential solution. Moreover, the integration of MPRS with other analytical methods including existing Raman spectroscopies could be a key for future development to realize both high sensitivity and selectivity. Most importantly, MPRS opens a new realm of innovation in water pollutant detection and Raman spectroscopy. From a material perspective, there is an unlimited design space for new combinations of MPs and analytes. From an instrumentation perspective, MPRS will promote the development of MP-decorated substrate manufacturing, narrow-band spectrum modules for specific MPs, and new portable and deployable testing platforms.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eCompeting interests\u003c/h2\u003e \u003cp\u003eB.L., L.Z., W.X., and C.G. filed a U.S. Provisional Patent. The remaining authors declare no competing interests.\u003c/p\u003e\u003ch2\u003eAuthor contributions\u003c/h2\u003e \u003cp\u003eConceptualization: L.Z., B.L.; Data curation: L.Z., J.H., C.G., A.D.; Formal analysis: L.Z., J. H., C.G., H.C., L.L., W.X., B.L.; Funding acquisition: W.X., B.L.; Investigation: L.Z., J.H., C.G., W.X., B.L.; Methodology: L.Z., J.H., C.G., A.D., H.C., J.W.; Project administration: L.L., W.X., B.L.; Supervision: L.L., W.X., B.L.; Visualization: L.Z., L.L., W.X., B.L.; Writing-original draft: L.Z., J.H., C.G., H.C., J.W., L.B., L.L., W.X., B.L.; Writing-review \u0026amp; editing: L.Z., J.H., J.W., L.B., L.L., W.X., B.L..\u003c/p\u003e\u003ch2\u003eAcknowledgements\u003c/h2\u003e \u003cp\u003eWe thank Dr. Gang Feng and Dr. Scott Dietrich at Villanova University for the support of Raman and AFM measurement; Dr. Xu Feng at the University of Delaware for the assistance and discussion with ToF-SIMS; and Dr. Sumbul Hafeez at Villanova University for the discussion on PFAS solution preparation. We also thank Mr. Rahul Sharma in Anton Paar USA, Inc. for the use of the portable Raman (Anton Paar CORA 5001 Raman spectrometer). L.Z., C.G., and B.L. were supported in part by the U.S. National Science Foundation (Grants # AM-2003077 and MRI-2018852). C. G., W.X., and B.L., acknowledge the support from the Dean\u0026rsquo;s Fellow of the College of Engineering, Villanova University. A.D. acknowledges the support from ME Junior Research Scholar, Department of Mechanical Engineering, Villanova University. L.B., J.W., and W.X. were funded in part by the Villanova University Research Catalyst Award. W.X. would like to acknowledge support by the U.S. Department of Defense through the Strategic Environmental Research and Development Program (SERDP ER23-3593).\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eGl\u0026uuml;ge, J.\u003cem\u003e et al.\u003c/em\u003e An overview of the uses of per- and polyfluoroalkyl substances (PFAS). \u003cem\u003eEnviron. Sci. Proc. Imp.\u003c/em\u003e \u003cstrong\u003e22\u003c/strong\u003e, 2345-2373 (2020).\u003c/li\u003e\n\u003cli\u003eEvich, M. G.\u003cem\u003e et al.\u003c/em\u003e Per-and polyfluoroalkyl substances in the environment. \u003cem\u003eScience\u003c/em\u003e \u003cstrong\u003e375\u003c/strong\u003e, eabg9065 (2022).\u003c/li\u003e\n\u003cli\u003eXiao, F.\u003cem\u003e et al.\u003c/em\u003e Cross-national challenges and strategies for PFAS regulatory compliance in water infrastructure. \u003cem\u003eNat. Water\u003c/em\u003e \u003cstrong\u003e1\u003c/strong\u003e, 1004-1015 (2023).\u003c/li\u003e\n\u003cli\u003eGao, J.\u003cem\u003e et al.\u003c/em\u003e Photochemical degradation pathways and near-complete defluorination of chlorinated polyfluoroalkyl substances. \u003cem\u003eNat. Water\u003c/em\u003e \u003cstrong\u003e1\u003c/strong\u003e, 381-390 (2023).\u003c/li\u003e\n\u003cli\u003eTokranov, A. K.\u003cem\u003e et al.\u003c/em\u003e Predictions of groundwater PFAS occurrence at drinking water supply depths in the United States. \u003cem\u003eScience\u003c/em\u003e \u003cstrong\u003e386\u003c/strong\u003e, 748-755 (2024).\u003c/li\u003e\n\u003cli\u003eChen, X.\u003cem\u003e et al.\u003c/em\u003e Quantifying indirect contribution from precursors to human body burden of legacy PFASs based on paired blood and one-week duplicate diet. \u003cem\u003eEnviron. Sci. Technol.\u003c/em\u003e \u003cstrong\u003e56\u003c/strong\u003e, 5632-5640 (2022).\u003c/li\u003e\n\u003cli\u003eBrunn, H.\u003cem\u003e et al.\u003c/em\u003e PFAS: forever chemicals-persistent, bioaccumulative and mobile. Reviewing the status and the need for their phase out and remediation of contaminated sites. \u003cem\u003eEnviron. Sci. Eur.\u003c/em\u003e \u003cstrong\u003e35\u003c/strong\u003e, 20 (2023).\u003c/li\u003e\n\u003cli\u003eNicole, W. (National Institute of Environmental Health Sciences, 2013).\u003c/li\u003e\n\u003cli\u003eLuo, Y.\u003cem\u003e et al.\u003c/em\u003e Prenatal exposure of PFAS in cohorts of pregnant women: identifying the critical windows of vulnerability and health implications. \u003cem\u003eEnviron. Sci. Technol.\u003c/em\u003e \u003cstrong\u003e58\u003c/strong\u003e, 13624\u0026minus;13635 (2024).\u003c/li\u003e\n\u003cli\u003eRead, R., Briefs, C. B. \u0026amp; Cases, C. C. C. PFAS National Primary Drinking Water Regulation 89 Fed. Reg. 32532 (Apr. 26, 2024) Copy Cite. \u003cem\u003eFederal Register\u003c/em\u003e (2024).\u003c/li\u003e\n\u003cli\u003ePoothong, S., Thomsen, C., Padilla-Sanchez, J. A., Papadopoulou, E. \u0026amp; Haug, L. S. Distribution of novel and well-known poly-and perfluoroalkyl substances (PFASs) in human serum, plasma, and whole blood. \u003cem\u003eEnviron. Sci. Technol.\u003c/em\u003e \u003cstrong\u003e51\u003c/strong\u003e, 13388-13396 (2017).\u003c/li\u003e\n\u003cli\u003eAl Amin, M.\u003cem\u003e et al.\u003c/em\u003e Recent advances in the analysis of per-and polyfluoroalkyl substances (PFAS)-A review. \u003cem\u003eEnviron. Technol. Innov.\u003c/em\u003e \u003cstrong\u003e19\u003c/strong\u003e, 100879 (2020).\u003c/li\u003e\n\u003cli\u003eDalapati, R., Hunter, M., Sk, M., Yang, X. \u0026amp; Zang, L. Fluorescence turn-on detection of perfluorooctanoic acid (PFOA) by perylene diimide-based metal-organic framework. \u003cem\u003eACS Appl. Mater. Interfaces\u003c/em\u003e \u003cstrong\u003e16\u003c/strong\u003e, 32344\u0026minus;32356 (2024).\u003c/li\u003e\n\u003cli\u003eZhang, K.\u003cem\u003e et al.\u003c/em\u003e Luminescence life time-based sensing platform based on cyclometalated Iridium (III) complexes for the detection of perfluorooctanoic acid in aqueous samples. \u003cem\u003eAnal. Chem.\u003c/em\u003e \u003cstrong\u003e96\u003c/strong\u003e, 1565-1575 (2024).\u003c/li\u003e\n\u003cli\u003eChen, Q., Zhu, P., Xiong, J., Gao, L. \u0026amp; Tan, K. A sensitive and selective triple-channel optical assay based on red-emissive carbon dots for the determination of PFOS. \u003cem\u003eMicrochem. J.\u003c/em\u003e \u003cstrong\u003e145\u003c/strong\u003e, 388-396 (2019).\u003c/li\u003e\n\u003cli\u003eConcell\u0026oacute;n, A., Castro-Esteban, J. \u0026amp; Swager, T. M. Ultratrace PFAS detection using amplifying fluorescent polymers. \u003cem\u003eJ. Am. Chem. Soc.\u003c/em\u003e \u003cstrong\u003e145\u003c/strong\u003e, 11420-11430 (2023).\u003c/li\u003e\n\u003cli\u003eZheng, Z.\u003cem\u003e et al.\u003c/em\u003e Guanidinocalix [5] arene for sensitive fluorescence detection and magnetic removal of perfluorinated pollutants. \u003cem\u003eNat. Commun.\u003c/em\u003e \u003cstrong\u003e10\u003c/strong\u003e, 5762 (2019).\u003c/li\u003e\n\u003cli\u003eConcell\u0026oacute;n, A. \u0026amp; Swager, T. M. Detection of per‐and polyfluoroalkyl substances (PFAS) by interrupted energy transfer. \u003cem\u003eAngew. Chem. Int. Ed.\u003c/em\u003e \u003cstrong\u003e62\u003c/strong\u003e, e202309928 (2023).\u003c/li\u003e\n\u003cli\u003ePark, S., Gordon, C. T. \u0026amp; Swager, T. M. Resistivity detection of perfluoroalkyl substances with fluorous polyaniline in an electrical lateral flow sensor. \u003cem\u003eProc. Nat. Acad. Sci. USA\u003c/em\u003e \u003cstrong\u003e121\u003c/strong\u003e, e2317300121 (2024).\u003c/li\u003e\n\u003cli\u003eTabar, F. A.\u003cem\u003e et al.\u003c/em\u003e Thermal determination of perfluoroalkyl substances in environmental samples employing a molecularly imprinted polyacrylamide as a receptor layer. \u003cem\u003eEnviron. Technol. Innov.\u003c/em\u003e \u003cstrong\u003e29\u003c/strong\u003e, 103021 (2023).\u003c/li\u003e\n\u003cli\u003eMashkoor, F.\u003cem\u003e et al.\u003c/em\u003e Freestanding WS\u003csub\u003e2\u003c/sub\u003e-MWCNT nanocomposite for electrochemical detection of contaminants of emerging concern-perfluorooctanoic acid \u0026ldquo;A Forever Chemical\u0026rdquo; and supercapacitor applications. \u003cem\u003eACS Sustain. Chem. Eng.\u003c/em\u003e \u003cstrong\u003e11\u003c/strong\u003e, 13306-13319 (2023).\u003c/li\u003e\n\u003cli\u003eTian, Q.\u003cem\u003e et al.\u003c/em\u003e Fluorine-functionalized MOF modified GCE for highly sensitive electrochemical detection of persistent pollutant perfluorooctanoic acid. \u003cem\u003eSensor. Actuat. B-Chem.\u003c/em\u003e \u003cstrong\u003e404\u003c/strong\u003e, 135309 (2024).\u003c/li\u003e\n\u003cli\u003eShanbhag, M. M.\u003cem\u003e et al.\u003c/em\u003e Hafnium doped tungsten oxide intercalated carbon matrix for electrochemical detection of perfluorooctanoic acid. \u003cem\u003eChem. Eng. J.\u003c/em\u003e \u003cstrong\u003e434\u003c/strong\u003e, 134700 (2022).\u003c/li\u003e\n\u003cli\u003eGumyusenge, A.\u003cem\u003e et al.\u003c/em\u003e Copper-based 2D conductive metal organic framework thin films for ultrasensitive detection of perfluoroalkyls in drinking water. (2022).\u003c/li\u003e\n\u003cli\u003eHafeez, S., Khanam, A., Cao, H., Chaplin, B. P. \u0026amp; Xu, W. Novel conductive and redox-active molecularly imprinted polymer for direct quantification of perfluorooctanoic acid. \u003cem\u003eEnviron. Sci. Technol. Lett.\u003c/em\u003e \u003cstrong\u003e11\u003c/strong\u003e, 871-877 (2024).\u003c/li\u003e\n\u003cli\u003eComnea-Stancu, I. R. \u0026amp; van Staden, J. K. F. Ultrasensitive detection of water pollutant PFOA based on AuNPs decorated NiOScZ screen-printed electrode. \u003cem\u003eJ. Environ. Chem. Eng.\u003c/em\u003e \u003cstrong\u003e12\u003c/strong\u003e, 113850 (2024).\u003c/li\u003e\n\u003cli\u003eMenger, R. F., Funk, E., Henry, C. S. \u0026amp; Borch, T. Sensors for detecting per-and polyfluoroalkyl substances (PFAS): A critical review of development challenges, current sensors, and commercialization obstacles. \u003cem\u003eChem. Eng. J.\u003c/em\u003e \u003cstrong\u003e417\u003c/strong\u003e, 129133 (2021).\u003c/li\u003e\n\u003cli\u003eGarg, S.\u003cem\u003e et al.\u003c/em\u003e Nano-enabled sensing of per-/poly-fluoroalkyl substances (PFAS) from aqueous systems-A review. \u003cem\u003eJ. Environ. Manag.\u003c/em\u003e \u003cstrong\u003e308\u003c/strong\u003e, 114655 (2022).\u003c/li\u003e\n\u003cli\u003eWang, Y., Darling, S. B. \u0026amp; Chen, J. Selectivity of per-and polyfluoroalkyl substance sensors and sorbents in water. \u003cem\u003eACS Appl. Mater. Interfaces\u003c/em\u003e \u003cstrong\u003e13\u003c/strong\u003e, 60789-60814 (2021).\u003c/li\u003e\n\u003cli\u003ePrakash, J. Ultrasensitive detection of emerging water contaminants using surface enhanced Raman scattering technique: Recent advancement, challenges and future prospects. \u003cem\u003eCurr. Opin. Environ. Sci. Health\u003c/em\u003e \u003cstrong\u003e39\u003c/strong\u003e, 100552 (2024).\u003c/li\u003e\n\u003cli\u003eLi, C., Fang, X., Li, H. \u0026amp; Zhang, X. Direct and rapid sensing of per-and polyfluoroalkyl substances using SERS-active optical fibers. \u003cem\u003eACS Appl. Opt. Mater.\u003c/em\u003e \u003cstrong\u003e2\u003c/strong\u003e, 610-616 (2024).\u003c/li\u003e\n\u003cli\u003eFeng, Y.\u003cem\u003e et al.\u003c/em\u003e Ag nanoparticle/Au@Ag nanorod sandwich structures for SERS-based detection of perfluoroalkyl substances. \u003cem\u003eACS Appl. Nano Mater.\u003c/em\u003e \u003cstrong\u003e6\u003c/strong\u003e, 13974-13983 (2023).\u003c/li\u003e\n\u003cli\u003ePark, H., Park, J., Kim, W., Kim, W. \u0026amp; Park, J. Ultra-sensitive SERS detection of perfluorooctanoic acid based on self-assembled p-phenylenediamine nanoparticle complex. \u003cem\u003eJ. Hazard. Mater.\u003c/em\u003e \u003cstrong\u003e453\u003c/strong\u003e, 131384 (2023).\u003c/li\u003e\n\u003cli\u003eMcDonnell, C.\u003cem\u003e et al.\u003c/em\u003e Aerosol jet printed surface-enhanced Raman substrates: application for high-sensitivity detection of perfluoroalkyl substances. \u003cem\u003eACS Omega\u003c/em\u003e \u003cstrong\u003e8\u003c/strong\u003e, 1597-1605 (2022).\u003c/li\u003e\n\u003cli\u003eBai, S.\u003cem\u003e et al.\u003c/em\u003e Plasmonic superstructure arrays fabricated by laser near-field reduction for wide-range sers analysis of fluorescent materials. \u003cem\u003eNanomaterials\u003c/em\u003e \u003cstrong\u003e12\u003c/strong\u003e, 970 (2022).\u003c/li\u003e\n\u003cli\u003eKrafft, M. P. \u0026amp; Riess, J. G. Chemistry, physical chemistry, and uses of molecular fluorocarbon-hydrocarbon diblocks, triblocks, and related compounds-Unique \u0026ldquo;Apolar\u0026rdquo; components for self-assembled colloid and interface engineering. \u003cem\u003eChem. Rev.\u003c/em\u003e \u003cstrong\u003e109\u003c/strong\u003e, 1714-1792 (2009).\u003c/li\u003e\n\u003cli\u003eZhao, L.\u003cem\u003e et al.\u003c/em\u003e Wafer-scale full-coverage self-limiting assembly of particles on flexible substrates. \u003cem\u003eACS Appl. Mater. Interfaces\u003c/em\u003e \u003cstrong\u003e14\u003c/strong\u003e, 46095-46102 (2022).\u003c/li\u003e\n\u003cli\u003eZhou, D.\u003cem\u003e et al.\u003c/em\u003e Ultrafast assembly and healing of nanomaterial networks on polymer substrates for flexible hybrid electronics. \u003cem\u003eAppl. Mater. Today\u003c/em\u003e \u003cstrong\u003e22\u003c/strong\u003e, 100956 (2021).\u003c/li\u003e\n\u003cli\u003eZhou, D.\u003cem\u003e et al.\u003c/em\u003e Ultrafast assembly and healing of nanomaterial networks on polymer substrates for flexible hybrid electronics. \u003cem\u003eACS Appl. Mater. Interfaces\u003c/em\u003e \u003cstrong\u003e11\u003c/strong\u003e, 33458-33464 (2019).\u003c/li\u003e\n\u003cli\u003eCai, W.\u003cem\u003e et al.\u003c/em\u003e Increasing ionic strength and valency of cations enhance sorption through hydrophobic interactions of PFAS with soil surfaces. \u003cem\u003eSci. Total Environ.\u003c/em\u003e \u003cstrong\u003e817\u003c/strong\u003e, 152975 (2022).\u003c/li\u003e\n\u003cli\u003eNguyen, T. M. H.\u003cem\u003e et al.\u003c/em\u003e Influences of chemical properties, soil properties, and solution pH on soil\u0026ndash;water partitioning coefficients of per-and polyfluoroalkyl substances (PFASs). \u003cem\u003eEnviron. Sci. Technol.\u003c/em\u003e \u003cstrong\u003e54\u003c/strong\u003e, 15883-15892 (2020).\u003c/li\u003e\n\u003cli\u003eRosenblum, L. \u0026amp; Wendelken, S. Method 533: determination of per-and polyfluoroalkyl substances in drinking water by isotope dilution anion exchange solid phase extraction and liquid chromatography/tandem mass spectrometry. \u003cem\u003eTandem Mass Spectrometry\u003c/em\u003e \u003cstrong\u003e52\u003c/strong\u003e (2019).\u003c/li\u003e\n\u003cli\u003eShoemaker, J. \u0026amp; Tettenhorst, D. Method 537.1: determination of selected per-and polyfluorinated alkyl substances in drinking water by solid phase extraction and liquid chromatography/tandem mass spectrometry (LC/MS/MS). \u003cem\u003eNational Center for Environmental Assessment, Washington, DC\u003c/em\u003e (2018).\u003c/li\u003e\n\u003cli\u003eShoemaker, J., Grimmett, P. \u0026amp; Boutin, B. Method 537. Determination of selected perfluorinated alkyl acids in drinking water by solid phase extraction and liquid chromatography/tandem mass spectrometry (LC/MS/MS). \u003cem\u003eTandem Mass Spectrometry (LC/MS/MS)\u003c/em\u003e (2009).\u003c/li\u003e\n\u003cli\u003eStuart, B. H. \u003cem\u003ePolymer analysis\u003c/em\u003e. (John Wiley \u0026amp; Sons, 2008).\u003c/li\u003e\n\u003cli\u003eZhao, L.\u003cem\u003e et al.\u003c/em\u003e Universal salt-assisted assembly of MXene from suspension on polymer substrates. \u003cem\u003eNat. Commun.\u003c/em\u003e \u003cstrong\u003e15\u003c/strong\u003e, 10027 (2024).\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"nature-portfolio","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"","title":"Nature Portfolio","twitterHandle":"","acdcEnabled":false,"dfaEnabled":false,"editorialSystem":"ejp","reportingPortfolio":"","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-5861495/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5861495/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003ePer- and poly-fluoroalkyl substances (PFAS) have received significant attention due to their persistence in the environment. Because of their accumulative nature, even trace amounts can adversely impact human health and ecosystems. Here, we present Molecule-Probed Raman Spectroscopy (MPRS), an ultra-sensitive, low-cost, and fast method that can achieve the femtogram-per-liter detection of PFAS, surpassing any existing methods by at least four orders of magnitude. In contrast to existing Raman Spectroscopy monitoring the spectrum of PFAS, MPRS monitors changes in the Raman spectrum of molecular probes, methyl group (-CH\u003csub\u003e3\u003c/sub\u003e) on polydimethylsiloxane, upon PFAS capture. MPRS succeeds in detecting multiple individual PFAS in water and monitoring PFAS in complex matrices such as surface water and human blood. We also demonstrated the feasibility of on-site monitoring of PFAS using a portable Raman spectrometer. Beyond its transformative detection capability, MPRS establishes a new analyte detection paradigm, paving the way for innovative material systems and instruments.\u003c/p\u003e","manuscriptTitle":"Molecule-Probed Raman Spectroscopy for Femtogram-per-Liter Level Per- and Polyfluoroalkyl Substances Detection","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-02-12 11:50:01","doi":"10.21203/rs.3.rs-5861495/v1","editorialEvents":[],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"nature-communications","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"NCOMMS","sideBox":"Learn more about [Nature Communications](http://www.nature.com/ncomms/)","snPcode":"","submissionUrl":"https://mts-ncomms.nature.com/","title":"Nature Communications","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"ejp","reportingPortfolio":"Nature Communications","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"7d2e5b68-d283-4b50-bb05-e8804716d773","owner":[],"postedDate":"February 12th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[{"id":44183995,"name":"Physical sciences/Materials science/Materials for devices/Sensors and biosensors"},{"id":44183996,"name":"Physical sciences/Materials science/Techniques and instrumentation/Characterization and analytical techniques"}],"tags":[],"updatedAt":"2025-07-30T19:15:16+00:00","versionOfRecord":[],"versionCreatedAt":"2025-02-12 11:50:01","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-5861495","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5861495","identity":"rs-5861495","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}