In Situ Growth of AuNPs on Glass Nanofibers for SERS Sensors

SERS-based microdevices for use as in vitro diagnostic biosensors

Advances in surface-enhanced Raman scattering (SERS) detection have helped to overcome the limitations of traditional in vitro diagnostic methods, such as fluorescence and chemiluminescence, owing to its high sensitivity and multiplex detection capability. However, for the implementation of SERS detection technology in disease diagnosis, a SERS-based assay platform capable of analyzing clinical samples is essential. Moreover, infectious diseases like COVID-19 require the development of point-of-care (POC) diagnostic technologies that can rapidly and accurately determine infection status. As an effective assay platform, SERS-based bioassays utilize SERS nanotags labeled with protein or DNA receptors on Au or Ag nanoparticles, serving as highly sensitive optical probes. Additionally, a microdevice is necessary as an interface between the target biomolecules and SERS nanotags. This review aims to introduce various microdevices developed for SERS detection, available for POC diagnostics, including LFA strips, microfluidic chips, and microarray chips. Furthermore, the article presents research findings reported in the last 20 years for the SERS-based bioassay of various diseases, such as cancer, cardiovascular diseases, and infectious diseases. Finally, the prospects of SERS bioassays are discussed concerning the integration of SERS-based microdevices and portable Raman readers into POC systems, along with the utilization of artificial intelligence technology.

Hydrogel-Coated SERS Microneedles for Drug Monitoring in Dermal Interstitial Fluid

In vivo drug monitoring is crucial for evaluating the effectiveness and safety of drug treatment. Blood sampling and analysis is the current gold standard but needs professional skills and cannot meet the requirements of point-of-care testing. Dermal interstitial fluid (ISF) showed great potential to replace blood for in vivo drug monitoring; however, the detection was challenging, and the drug distribution behavior in ISF was still unclear until now. In this study, we proposed surface-enhanced Raman spectroscopy (SERS) microneedles (MNs) for the painless and real-time analysis of drugs in ISF after intravenous injection. Using methylene blue (MB) and mitoxantrone (MTO) as model drugs, the innovative core-satellite structured Au@Ag SERS substrate, hydrogel coating over the MNs, rendered sensitive and quantitative drug detection in ISF of mice within 10 min. Based on this technique, the pharmacokinetics of the two drugs in ISF was investigated and compared with those in blood, where the drugs were analyzed via liquid chromatography-mass spectrometry. It was found that the MB concentration in ISF and blood was comparable, whereas the concentration of MTO in ISF was 2-3 orders of magnitude lower than in blood. This work proposed an efficient tool for ISF drug monitoring. More importantly, it experimentally proved that the penetration ratio of blood to ISF was drug-dependent, providing insightful information into the potential of ISF as a blood alternative for in vivo drug detection.

Block copolymer-templated surface-enhanced Raman scattering-active nanofibers for hydrogen sulfide detection

Metabolic disorders involving endogenous H2S have been linked to a variety of serious human diseases, particularly cancer. In this study, we employed nanofibers with surface-enhanced Raman scattering (SERS) activity for the detection of H2S within live cells. These nanofibers were chosen for their minimal invasiveness, high spatial resolution, and enhanced SERS sensitivity. To improve the performance of SERS, highly sensitive core-shell multibranched-Au NPs (MBAuNP)@Ag NPs were decorated on the nanofibers as SERS tags for H2S detection. A SERS probe named MBN, embedded between the Au core and Ag shell, was utilized for quantitative detection. These nanofibers exhibited excellent reproducibility (relative standard deviation (RSD) within 5.7 %) and demonstrated a strong linear relationship with sulfide concentrations ranging from 50 nM to 1 μM, with an estimated detection limit of 0.12 nM. As a proof of concept, the aforementioned nanofibers were successfully applied to detect endogenous H2S in living cells, offering a potential analytical method in the related research of detection.

Bleach Cleaning of Commercially Available Gold Nanopillar Arrays for Surface-Enhanced Raman Spectroscopy (SERS)

Surface-enhanced Raman spectroscopy (SERS) is a highly sensitive technique that can assist in trace analysis for biomedical, diagnostic, and environmental applications. However, a major limitation of SERS is surface contamination of the substrates used, which can complicate the spectral reproducibility, limits of detection, and detection of unknown analytes. This is especially prevalent with commercially available substrates as shipping under a controlled and clean environment is difficult. Here we report a method using dilute bleach solutions to remove surface contamination from commercially available substrates consisting of gold-coated nanopillar arrays that maintains functionality. The results show that this method can be used to remove background signals associated with typical surface contamination in commercially available substrates as well as remove thiolated self-assembled monolayers (SAMs). Results indicate the bleach oxidizes the surface contaminants, which can then be easily washed away. Although the metallic surface also becomes oxidized in this process, the surface can be reduced without loss of SERS activity. The SERS intensity of SAMs improved following bleach treatment across all concentrations studied.

Recent Development of Polymer Nanofibers in the Field of Optical Sensing

In recent years, owing to the continuous development of polymer nanofiber manufacturing technology, various nanofibers with different structural characteristics have emerged, allowing their application in the field of sensing to continually expand. Integrating polymer nanofibers with optical sensors takes advantage of the high sensitivity, fast response, and strong immunity to electromagnetic interference of optical sensors, enabling widespread use in biomedical science, environmental monitoring, food safety, and other fields. This paper summarizes the research progress of polymer nanofibers in optical sensors, classifies and analyzes polymer nanofiber optical sensors according to different functions (fluorescence, Raman, polarization, surface plasmon resonance, and photoelectrochemistry), and introduces the principles, structures, and properties of each type of sensor and application examples in different fields. This paper also looks forward to the future development directions and challenges of polymer nanofiber optical sensors, and provides a reference for in-depth research of sensors and industrial applications of polymer nanofibers.

Design and Synthesis of SERS Materials for In Vivo Molecular Imaging and Biosensing

Surface-enhanced Raman scattering (SERS) is a feasible and ultra-sensitive method for biomedical imaging and disease diagnosis. SERS is widely applied to in vivo imaging due to the development of functional nanoparticles encoded by Raman active molecules (SERS nanoprobes) and improvements in instruments. Herein, the recent developments in SERS active materials and their in vivo imaging and biosensing applications are overviewed. Various SERS substrates that have been successfully used for in vivo imaging are described. Then, the applications of SERS imaging in cancer detection and in vivo intraoperative guidance are summarized. The role of highly sensitive SERS biosensors in guiding the detection and prevention of diseases is discussed in detail. Moreover, its role in the identification and resection of microtumors and as a diagnostic and therapeutic platform is also reviewed. Finally, the progress and challenges associated with SERS active materials, equipment, and clinical translation are described. The present evidence suggests that SERS could be applied in clinical practice in the future.

Skin Interstitial Fluid-Based SERS Tags Labeled Microneedles for Tracking of Peritonitis Progression and Treatment Effect

Skin interstitial fluid (ISF)-based microneedle (MN) sensing has recently exhibited wide promise for the minimally invasive and painless diagnosis of diseases. However, it is still a great challenge to diagnose more disease types due to the limited in situ sensing techniques and insufficient ISF biomarker sources. Herein, ISF is employed to pioneer the tracking of acute peritonitis progression via surface-enhanced Raman scattering (SERS) tags labeled MNs patch technique. Densely deposited core-satellite gold nanoparticles and 3-mercaptophenylboronic acid as a Raman reporter enable the developed MNs patch with high sensitivity and selectivity in the determination of H₂O₂, an indicator of peritonitis development. Importantly, the MNs patch not only reliably tracks the different states of peritonitis but also evaluates the efficacy of drugs in the treatment of peritonitis, as evidenced by the altered SERS signal consistent with plasma pro-inflammatory factor (TNF-α) and peritoneum pathological manifestations. Interestingly, the major source of H₂O₂ in ISF of acute peritonitis investigated may not be through conventional blood capillary filtration pathway. This work provides a new route and technique for the early diagnosis of acute peritonitis and the evaluation of drug therapy effects. The developed MNs patch is promising to serve as a universal sensing tool to greatly enrich the variety and prospect of ISF-based disease diagnosis.

Highly sensitive SERS detection in a non-volatile liquid-phase system with nanocluster-patterned optical fiber SERS probes

The use of surface-enhanced Raman scattering (SERS) spectroscopy for the detection of substances in non-volatile systems, such as edible oil and biological cells, is an important issue in the fields of food safety and biomedicine. However, traditional dry-state SERS detection with planar SERS substrates is not suitable for highly sensitive and rapid SERS detection in non-volatile liquid-phase systems. In this paper, we take contaminant in edible oil as an example and propose an in situ SERS detection method for non-volatile complex liquid-phase systems with high-performance optical fiber SERS probes. Au-nanorod clusters are successfully prepared on optical fiber facet by a laboratory-developed laser-induced dynamic dip-coating method, and relatively high detection sensitivity (LOD of 2.4 × 10^-6 mol/L for Sudan red and 3.6 × 10^-7 mol/L for thiram in sunflower oil) and good reproducibility (RSD less than 10%) are achieved with a portable Raman spectrometer and short spectral integration time of 10 s even in complex edible oil systems. Additionally, the recovery rate experiment indicates the reliability and capability of this method for quantitative detection applications. This work provides a new insight for highly sensitive and rapid SERS detection in non-volatile liquid-phase systems with optical fiber SERS probes and may find important practical applications in food safety and biomedicine.

Paper-Based Substrate for a Surface-Enhanced Raman Spectroscopy Biosensing Platform-A Silver/Chitosan Nanocomposite Approach

Paper is a popular platform material in all areas of sensor research due to its porosity, large surface area, and biodegradability, to name but a few. Many paper-based nanocomposites have been reported in the last decade as novel substrates for surface-enhanced Raman spectroscopy (SERS). However, there are still limiting factors, like the low density of hot spots or loss of wettability. Herein, we designed a process to fabricate a silver-chitosan nanocomposite layer on paper celluloses by a layer-by-layer method and pH-triggered chitosan assembly. Under microscopic observation, the resulting material showed a nanoporous structure, and silver nanoparticles were anchored evenly over the nanocomposite layer. In SERS measurement, the detection limit of 4-aminothiophenol was 5.13 ppb. Furthermore, its mechanical property and a strategy toward further biosensing approaches were investigated.

Gold Nanoparticle-Based Photo-Cross-Linking Strategy for Cellular Target Identification of Supercomplex Molecular Systems

Cellular target identification plays an essential role in innovative drug development and pharmacological mechanism elucidation. However, very few practical experimental methodologies have been developed for identifying target proteins for supercomplex molecular systems such as biologically active phytochemicals or pharmaceutical compositions. To overcome this limitation, we synthesized gold nanoparticles (AuNPs) as solid scaffolds, which were bound with 4,4'-dihydroxybenzophenone (DHBP) as a photo-cross-linking group on the surface. Then, DHBP-modified AuNPs cross-linked various organic compounds from phytochemicals under ultraviolet radiation via carbene reactions, H-C bond insertion, for catalytic C-C bond formation. We next used the phytochemical-cross-linked AuNPs (phytoAuNPs) to pull down potential binding proteins from brain tissue lysate and identified 13 neuroprotective targets by mass spectrometry analysis. As an exemplary study, we selected Hsp60 as a crucial cellular target to further screen 14 target-binding compounds from phytochemicals through surface plasmon resonance (SPR) analysis, followed by Hsp60 activity detection and neuroprotective effect assay in cells. Collectively, this gold nanoparticle-based photo-cross-linking strategy can serve as a useful platform for discovering novel cellular targets for supercomplex molecular systems and help to explore pharmacological mechanisms and active substances.

Widely tunable surface plasmon resonance and uniquely superior SERS performance of Au nanotube network films

Three-dimensional Au network films with flexibility and transferability were fabricated based on sputtering deposition onto electrospun nanofibers as a template. The films are constructed using long Au nanotubes that are cross-linked with each other and that have dense nanoparticles on the tube wall surface. The surface plasmon resonance (SPR) peaks for the films are tunable in a wide range, from visible light to the near-infrared region, by tuning the inner diameter and/or wall thickness of the nanotubes. Such structured film exhibits significant surface-enhanced Raman scattering (SERS) activity with good signal uniformity and stability, and possesses great potential in thein situdetection of trace organic pollutants on a solid surface by simple transferring. This study provides a Au film with a unique structure and widely tunable SPR forin situSERS sensing and other needs.

Surface-Enhanced Raman Scattering Optophysiology Nanofibers for the Detection of Heavy Metals in Single Breast Cancer Cells

Mercury(II) ions (Hg²⁺) and silver ions (Ag⁺) are two of the most hazardous pollutants causing serious damage to human health. Here, we constructed surface-enhanced Raman scattering (SERS)-active nanofibers covered with 4-mercaptopyridine (4-Mpy)-modified gold nanoparticles to detect Hg²⁺ and Ag⁺. Experimental evidence suggests that the observed spectral changes originate from the combined effect of (i) the coordination between the nitrogen on 4-Mpy and the metal ions and (ii) the 4-Mpy molecular orientation (from flatter to more perpendicular with respect to the metal surface). The relative intensity of a pair of characteristic Raman peaks (at ∼428 and ∼708 cm^-1) was used to quantify the metal ion concentration, greatly increasing the reproducibility of the measurement compared to signal-on or signal-off detection based on a single SERS peak. The detection limit of this method for Hg²⁺ is lower than that for the Ag⁺ (5 vs 100 nM), which can be explained by the stronger interaction energy between Hg²⁺ and N compared to Ag⁺ and N, as demonstrated by density functional theory calculations. The Hg²⁺ and Ag⁺ ions can be masked by adding ethylenediaminetetraacetate and Cl^-, respectively, to the Hg²⁺ and Ag⁺ samples. The good sensitivity, high reproducibility, and excellent selectivity of these nanosensors were also demonstrated. Furthermore, detection of Hg²⁺ in living breast cancer cells at the subcellular level is possible, thanks to the nanometric size of the herein described SERS nanosensors, allowing high spatial resolution and minimal cell damage.