Ultrasonic-Assisted Synthesis of Highly Defined Silver Nanodimers by Self-Assembly for Improved Surface-Enhanced Raman Spectroscopy

Nanomaterials meet surface-enhanced Raman scattering towards enhanced clinical diagnosis: a review

Surface-enhanced Raman scattering (SERS) is a very promising tool for the direct detection of biomarkers for the diagnosis of i.e., cancer and pathogens. Yet, current SERS strategies are hampered by non-specific interactions with co-existing substances in the biological matrices and the difficulties of obtaining molecular fingerprint information from the complex vibrational spectrum. Raman signal enhancement is necessary, along with convenient surface modification and machine-based learning to address the former issues. This review aims to describe recent advances and prospects in SERS-based approaches for cancer and pathogens diagnosis. First, direct SERS strategies for key biomarker sensing, including the use of substrates such as plasmonic, semiconductor structures, and 3D order nanostructures for signal enhancement will be discussed. Secondly, we will illustrate recent advances for indirect diagnosis using active nanomaterials, Raman reporters, and specific capture elements as SERS tags. Thirdly, critical challenges for translating the potential of the SERS sensing techniques into clinical applications via machine learning and portable instrumentation will be described. The unique nature and integrated sensing capabilities of SERS provide great promise for early cancer diagnosis or fast pathogens detection, reducing sanitary costs but most importantly allowing disease prevention and decreasing mortality rates.

Facile and robust fabrication of hierarchical Au nanorods/Ag nanowire SERS substrates for the sensitive detection of dyes and pesticides

Surface enhanced Raman spectroscopy (SERS) has emerged as a promising tool for the rapid and ultrasensitive recognition of trace amounts of environmental pollutants. Hierarchical SERS substrates usually show superior performance to single-component substrates but require complicated preparation protocols. Herein, a facile, robust and low-cost route for the fabrication of hierarchical SERS substrates has been reported, in which no complicated laborious protocols or sophisticated equipment is needed. In the hierarchical SERS substrate, Au nanorods were distributed onto the network of Ag nanowires through evaporation induced self-assembly. The density of the Au nanorods and Ag nanowires could be easily tailored by tuning the number of droplets of gold nanorod solution and the concentration of silver nanowire solution. The nanogaps formed between Au nanorods and Ag nanowires were able to induce a rich enhanced electromagnetic field area via localized surface plasmon resonances and surface plasmon polaritons to achieve amplification of the Raman signal. The as-prepared substrate showed high uniformity and was capable of identifying 10^-12 M rhodamine 6G, 10^-10 M thiram and 10^-10 M crystal violet, with correlation coefficients (R²) all higher than 0.98. This approach can be employed for the detection of trace dyes, pesticides or other environmental pollutants with high sensitivity and uniformity.

Development of affinity between target analytes and substrates in surface enhanced Raman spectroscopy for environmental pollutant detection

Environmental pollution has long been a social concern due to the variety of pollutants and their wide distribution, persistence and being detrimental to health. It is therefore necessary to develop rapid and sensitive strategies to trace and detect these compounds. Among various detection methodologies, surface enhanced Raman spectroscopy (SERS) has become an attractive option as it enables accurate analyte identification, simple sample preparation, rapid detection and ultra-high sensitivity without any interference from water. For SERS detection, an essential yet challenging step is the effective capture of target analytes onto the surface of metal nanostructures with a high intensity of enhanced electromagnetic field. This review has systematically summarized recent advances in developing affinity between targets and the surface of SERS substrates via direct adsorption, hydrophobic functional groups, boronate affinity, metal organic frameworks (MOFs), DNA aptamers and molecularly imprinted polymers (MIPs). At the end of this review, technical limitations and outlook have been provided, with suggestions on optimizing SERS techniques for real-world applications in environmental pollutant detection.

Ultrasonic-Assisted Synthesis of Highly Defined Silver Nanodimers by Self-Assembly for Improved Surface-Enhanced Raman Spectroscopy

Considerable research efforts have been devoted to surface-enhanced Raman spectroscopy (SERS), due to its excellent performance in biosensing and imaging. Here, a novel and facile strategy for the fabrication of well-defined and uniform nanodimers as SERS substrates is presented. By the assistance of ultrasound, the violent polyol process for particle generation becomes controllable, enabling the self-assembly of nanostars to nanodimers. Moreover, the aggregation of nanodimers can be easily tuned by post-ultrasonic treatment, which gives a sensitive substrate for SERS.