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To develop operative surface-enhanced Raman spectroscopy (SERS) sensors, nanostructures with high signal enhancement and ease of production are highly desired. The SERS-active nanoparticle-gap-film (NGF) sandwich substrate using graphene as the gap nanospacer is of particular interest due to its strong local field enhancement associated with the atomically thin graphene gap. However, the complexity in fabricating such nanostructures, especially the often involved high-temperature and vacuum processes, ultimately hampers practical applications. Here, a simple and low-cost SERS-active NGF sensor is demonstrated in which a graphene-based nanospacer was prepared by a one-step transfer-free mechanical milling process under amiable conditions. Notably, the milling process can readily produce and deposit the graphene nanospacer in a single fabrication step onto the desired metal substrates. To further enhance SERS performance, shape-anisotropic triangular silver nanoprisms were introduced into the NGF system, which offered enhanced Raman gain compared to spherical silver nanoparticles. Using Rhodamine 6G as the probe, the NGF SERS sensors exhibited a high sensitivity with a low detection limit of 5 × 10−9M with an enhancement factor of 2.7 × 105. This study opens up a new route for the facile production of cost-effective graphene-based NGF substrates for various SERS sensing applications. [ABSTRACT FROM AUTHOR]

Surface-enhanced Raman spectroscopy offers great potential for rapid and highly sensitive detection of pharmaceuticals from environmental sources. Herein, we investigated the feasibility of label-free sensing of antibiotic residues from wastewater effluents with high specificity by combining with multivariate analysis. Highly ordered silver nanoarrays with ∼34 nm roughness have been fabricated using a cost-effective electroless deposition technique. As-fabricated Ag arrays showed superior LSPR effects with an enhancement factor of 8 × 107. Excellent reproducibility has also been noticed with RSD values within 11%, whilst the sensor showed good stability and reusability characteristics for being used as a low-cost and reusable sensor. SERS studies demonstrated that antibiotics-spiked wastewater effluents can be detected with high efficiency in a label-free method. The molecular fingerprint bands of antibiotics such as sulfamethoxazole, sulfadiazine, and ciprofloxacin were well analyzed in effluent, tap, and deionized water. It has been found that antibiotics can be detected near picomolar levels; meanwhile, liquid chromatography-mass spectrometry (LC-MS) exhibited a detection limit within nanomolar concentrations only. Furthermore, the specificity of SERS sensing has been further analyzed using a multivariate analysis method, principal component analysis followed by linear discriminant analysis (PCA-LDA); which showed prominent discrimination to distinguish each antibiotic residue from wastewater effluents. The current study presented the potential of Ag nanoarray sensors for rapid, highly specific, and cost-effective analysis of pharmaceutical products for environmental remediation applications. [Display omitted] • High-performance Ag nanoarrays were facile fabricated for SERS sensing. • Excellent efficiency, reproducibility and reusability were established. • Rapid, label-free sensing of antibiotics including SMX, SDZ and CPX was investigated. • Picomolar detection limit was established for antibiotics spiked wastewater effluents. • Multivariate analysis revealed the high specificity of direct SERS sensing. [ABSTRACT FROM AUTHOR]

Surface-enhanced Raman spectroscopy (SERS) significantly amplifies the Raman scattering of molecules, enhancing their signals by several orders of magnitude. This emergent SERS-based optical detection strategies have attracted enormous research potential. In the current global context, the prevalence of environmental pollutants poses a critical concern that demands immediate attention, and hence this field requires the exploration of smart and advanced quality control tools. The advancement of SERS presents a promising path for monitoring and remediating environmental pollutants. By careful nanostructure design with enhanced surface plasmon resonance (SPR), SERS achieves rapid analysis, precise fingerprint specificity, and remarkable sensitivity nearing single molecule detection. Supported by portable Raman devices, SERS now emerges as a pivotal tool in addressing on-site environmental remediation challenges. In this review, we have summarized the developments in SERS-based strategies for environmental monitoring. Moreover, the correlation between SERS substrates and efficient environmental tracking is explored, addressing the need for precise monitoring both remotely and on-site. From a future perspective, the next level of research needed in advancing SERS sensors to practical purposes is also scrutinized. [ABSTRACT FROM AUTHOR]

[Display omitted] • Anisotropic AuAg nanoparticles were fabricated by chemical method. • Morphological properties of AuAg immobilized Ti sheets were correlated to SERS properties. • Picomolar and nanomolar levels of sensitivity obtained for melamine spiked water and milk samples respectively. • Sensors demonstrated excellent efficiency, reproducibility, and recyclability. • Real-time melamine sensing from commercial milk showed no presence of any melamine residues. As the degree of anisotropy in nanoparticle morphology increases, the resulting electromagnetic enhancement can be significantly intensified. Herein, we have attempted to develop anisotropic gold-silver (a-AuAg) nanoparticles deposited on a titanium sheet (a-AuAg@Ti) as a highly efficient Surface-enhanced Raman Spectroscopy (SERS) sensor for rapid detection of health-hazardous milk adulterants like melamine. Hierarchical a-AuAg nanoparticles have been synthesized via a facile seed and growth-mediated method, followed by immobilization on a titanium sheet using a drop-casting technique. The structural, morphological, chemical, and optical properties of a-AuAg@Ti sensors have been systematically investigated and correlated with their respective SERS performance. Morphological analysis revealed the occurrence of triangular, hexagonal, and pentagonal-shaped nanoparticles with an average particle size of ∼ 23 to 26 nm. Preliminary SERS analysis using Rhodamine 6G (R6G) probe molecule revealed significantly higher SERS activity for a-AuAg nanoparticles compared to their spherical counterparts. This could be attributed to the lightning rod effect associated with the synthesized anisotropic nanostructures. An enhancement factor of 1.7 x 108 has been estimated for a-AuAg@Ti sensor with excellent signal reproducibility. Further, the efficacy of melamine detection has been investigated by spiking it into water and milk samples. The estimated lower detection limit (LDL) near picomolar and nanomolar concentrations have been obtained for melamine-spiked samples in water and milk, respectively. High-performance liquid chromatography analysis for melamine revealed an LDL of only 0.1 µM, indicating the higher sensitivity of a-AuAg@Ti SERS sensor. Moreover, we have also analyzed commercial milk products to verify the melamine contents, but none of them showed melamine-specific fingerprint bands. Our findings highlight the superior sensitivity of a-AuAg@Ti substrates for real-time melamine detection, making them excellent optical sensing tools for food safety analysis. [ABSTRACT FROM AUTHOR]

The design of smart and advanced sensors facilitates highly sensitive optical detection platforms for biomolecules. Herein, we attempted the confined assembly of silver nanoprisms (SNPs) on hydrophobic Teflon tapes to design a highly flexible and ultrasensitive biosensing platform for DNA and glucose. We investigated the sensor characteristics including morphological, optical, and SERS activities as a function of nanoparticle size. Pyramidal SNPs were synthesized, whose size was tuned by varying the bromide ion concentrations. The size of SNPs was decreased with an increase in bromide ion concentrations, where quasi-spherical nanoparticles were formed at higher bromide content. The hydrophobic Teflon surface caused considerable constrain during the evaporation of nanoparticle suspension, leading to highly confined SNPs. SERS activities of Teflon/SNP sensors were tuned by varying the size of SNPs, where a size of ∼34 nm exhibited the highest signal enhancement. The optimum Teflon/SNP sensor showed an enhancement factor of 1.3 × 109 with high stability and excellent reproducibility. Teflon/SNP sensor was further exploited to detect DNA and glucose in a label-free method, exhibiting sensitivities of approximately 13.6 fg/µL and 5 µM, respectively. Real-time monitoring of DNA and glucose from saliva was also investigated. Teflon/SNP substrates were found to be excellent biosensing platforms for ultralow-level sensing of biomolecules in a rapid and cost-effective manner. [Display omitted] • Size tunable silver nanoprisms (SNPs) were synthesized and characterized. • Morphological and structural properties of SNPs were well elucidated. • Confined assembling of SNPs was achieved using hydrophobic condensation. • Teflon/SNP sensor exhibited high EF and reproducibility. • Developed sensor detected DNA and glucose with high sensitivity. • Real-time sensing from saliva was demonstrated. [ABSTRACT FROM AUTHOR]

Exploration of novel strategies for fabricating SERS substrates attracted enormous research potential as achieving high sensitivity, reproducibility along with cost effectiveness is really challenging. Herein, we have fabricated hierarchical silver nanoprism/graphene oxide/silicon nanowire (Ag/GO/SiNWs) arrays as surface-enhanced Raman scattering (SERS) sensors for the effective detection of atrazine. Homogenous and vertically aligned SiNWs have been successfully synthesized using silver assisted chemical etching. Further, Ag/GO/SiNWs arrays were assembled by subsequent spin-coating of GO followed by drop-casting deposition of Ag nanoprisms. Micro-structural properties of as-fabricated nano-arrays have been well examined by scanning electron and atomic force microscopic techniques. Nanowire bunches have been decorated by GO layers; which further facilitates homogenous deposition of Ag nanoprisms. Using rhodamin 6G as probe molecule, high SERS activity and excellent reproducibility of as-fabricated substrates have been demonstrated. High efficiency of 3.2 × 108 and was obtained for the fabricated sensors; attributed to the synergetic charge transfer between GO and Ag nanoprisms on high surface area Si nanowires. Charge transfer mechanism that leading to enhanced surface plasmon resonance effect of the as-fabricated array was established as well. Further, these low cost Ag/GO/SiNWs sensors exhibited ultrasensitive detection of pollutants such as methylene blue and atrazine residues down to picomolar levels; these can serve as potential chemical sensors for rapid monitoring of environmental pollutants in trace levels. [Display omitted] • Novel silver nanoprism-Graphene Oxide-Silicon Nanowire sensors were fabricated. • Micro-structural characteristics of sensor were well elucidated. • Nano-arrays exhibited superior sensitivity and reproducibility. • SERS enhancement factor of 3.2 × 1010 was obtained. • Hierarchial structures detected atrazine down to picomolar levels. [ABSTRACT FROM AUTHOR]