Synthesis of PVDF membrane loaded with wrinkled Au NPs for sensitive detection of R6G

Silver nanoparticles modified sulfur-containing POSS polymer membrane substrate for adsorption and surface-enhanced Raman scattering analysis of chrysoidine in food samples

In analysis of complex samples, the stability and sensitivity of surface-enhanced Raman scattering (SERS) substrates may be compromised by matrix interference. To address this issue, a membrane substrate was prepared for fast enrichment, separation, and detection of chrysoidine all-in-one. The silver nanoparticles modified sulfur-containing POSS polymer (AgNPs/POSS-P-S) SERS membrane substrate was fabricated using polyhedral oligomeric silsesquioxane (POSS) as support materials. Through in-situ growth, AgNPs were uniformly modified on POSS-P-S to ensure the stability and SERS activity of the membrane substrate. The enhancement factor of the malachite green was up to 5.3 × 105. By loading the AgNPs/POSS-P-S on membrane, on the other hand, the SERS membrane substrate can also serve as an adsorption medium for separating chrysoidine from sample matrix. Furthermore, the specific sensing mechanism of AgNPs/POSS-P-S for chrysoidine was investigated and a fast, sensitive, and selective method for its quantification was established, with a linear range of 0.010-2.0 mg/L and the limits of detection at 3.7 μg/L. In addition, the SERS method was successfully applied for the analysis of chrysoidine in beverages and chili products with the recoveries in the range of 83.5%-113.4 % and the relative standard deviations in 3.2%-9.0 %. The proposed AgNPs/POSS-P-S membrane based SRES method has great potential for rapid chrysoidine analysis in food samples.

Solid chip-based detection of trace morphine in solutions via portable surface-enhanced Raman spectroscopy

The accurate, sensitive and portable detection of morphine is important to handle judicial cases, but remains to be a great challenge. In this work, a flexible route is presented for the accurate identification and efficient detection of trace morphine in solutions based on surface-enhanced Raman spectroscopy (SERS) and a solid substrate/chip. A gold-coated jagged silicon nanoarray (Au-JSiNA) is designed and prepared via Si-based polystyrene colloidal template-reactive ion etching and sputtering deposition of Au. Such Au-JSiNA has three-dimensional nanostructure with good structural uniformity, high SERS activity and hydrophobic surface. Adopting this Au-JSiNA as SERS chip, trace morphine in solutions could be detected and identified in both dropping and soaking ways, and the limit of detection is below 10-4 mg/mL. Importantly, such chip is especially suitable for the detection of trace morphine in aqueous solutions and even domestic sewage. The good SERS performance is attributed to the high-density nanotips and nanogaps on this chip as well as its hydrophobic surface. Additionally, the appropriate surface modification of this Au-JSiNA chip with 3-mercapto-1-propanol or 3-mercaptopropionic acid/1-(3-dimethylaminopropyl)-3-ethylcarbodiimide can further increase its SERS performances to morphine. This work provides a facile route and practical solid chip for SERS detection of trace morphine in solutions, which is significant to develop the portable and reliable instruments for on-site analysis of drugs in solutions.

Flexible SERS Biosensor Based on Core-Shell Nanotags for Sensitive and Multiple Detection of T1DM Biomarkers

Sensitive and multiple detection of the biomarkers of type 1 diabetes mellitus (T1DM) is vital to the early diagnosis and clinical treatment of T1DM. Herein, we developed a SERS-based biosensor using polyvinylidene fluoride (PVDF) membranes as a flexible support for the detection of glutamic acid decarboxylase antibodies (GADA) and insulin autoantibodies (IAA). Two kinds of silver-gold core-shell nanotags embedded with Raman probes and attached with GADA or IAA antibodies were synthesized to capture the targets, enabling highly sensitive and highly selective detection of GADA and IAA. The embedded Raman probes sandwiched between silver and gold layers guaranteed spectral stability and reliability. Moreover, the utilization of two Raman probes enables simultaneous and multiplexing detection of both GADA and IAA, improving the detection accuracy for T1DM. The proposed SERS-based method has been proven feasible for clinical sample detection, demonstrating its great potential in sensitive, reliable, and rapid diagnosis of T1DM.

Stretchable and Flexible Micro-Nano Substrates for SERS Detection of Organic Dyes

Surface-enhanced Raman spectroscopy (SERS) is a precise and noninvasive analytical technique to identify vibrational fingerprints of trace analytes with sensitivity down to the single-molecule level. However, substrates can influence this capability, and current SERS techniques lack uniform, reproducible, and stable substrates to control plasma hot spots over a wide spectral range. Herein, we demonstrate a flexible SERS substrate via longitudinal stretching of a polydimethylsiloxane (PDMS) film. This substrate, after stretching and shrinking, exhibits an irregular wrinkled structure with abundant gaps and grooves that function as hot spots, thereby improving the hydrophobic properties of the material. To investigate the enhancement effect of Raman signals, silver nanoparticles (AgNPs) were mixed with Rhodamine 6G (R6G) solution, and the obtained blend was dropped onto the PDMS film to form a coffee ring pattern. According to the results, the hydrophobicity of the substrate increases with the degree of PDMS stretching, achieving the optimal level at 150% stretching. Moreover, the increase in hydrophobicity makes the measured molecules more aggregated, which enhances the Raman signal. The stretching and shrinkage of the PDMS film lead to a much higher density of nanogaps among nanoparticles and nanogrooves, which serve as multiple hot spots. Being highly localized regions of intense local fields, these hot spots make a significant contribution to SERS performance, improving the sensitivity and reproducibility of the method. In particular, the relative standard deviation (RSD) was found to be 2.5544%, and the detection limit was 1 × 10^-7 M. Therefore, SERS using stretchable and flexible micro-nano substrates is a promising way for detecting dyes in wastewater.

Increasing hotspots density for high-sensitivity SERS detection by assembling array of Ag nanocubes

Trace analysis has great promise in the fields of disease diagnosis and environment protection. Surface-enhanced Raman scattering (SERS) has wide range of utilization due to its reliable fingerprint detection. However, the sensitivity of SERS still needs to be enhanced. Raman scattering of target molecules around hotspots, the area with extremely strong electromagnetic field, can be highly amplified. Therefore, to increase the density of hotspots is one of the major approaches for enhancing the detection sensitivity of target molecules. In this paper, an ordered array of Ag nanocubes was assembled on a thiol modified silicon substrate as a SERS substrate, which provided high-density hotspots. The detection sensitivity is demonstrated by the limit of detection, which is down to 10^-6 nM with Rhodamine 6G as probe molecule. The wide linear range (10^-7-10^-13 M) and low relative standard deviation (<6.48%) indicate the good reproducibility of the substrate. Furthermore, the substrate can be used for the detection of dye molecules in lake water. This method provides an approach for increasing hotspots of SERS substrate, which could be a promising method to achieve good reproducibility and high sensitivity.