Silver overlayer-modified surface-enhanced Raman scattering-active gold substrates for potential applications in trace detection of biochemical species

Facile Fabrication of a Silver Nanoparticle Immersed, Surface-Enhanced Raman Scattering Imposed Paper Platform through Successive Ionic Layer Absorption and Reaction for On-Site Bioassays

We introduce a novel, facile, rapid, low-cost, highly reproducible, and power-free synthesizable fabrication method of paper-based silver nanoparticle (AgNP) immersed surface-enhanced Raman scattering (SERS) platform, known as the successive ionic layer absorption and reaction (SILAR) method. The rough and porous properties of the paper led to direct synthesis of AgNPs on the surface as well as in the paper due to capillary effects, resulting in improved plasmon coupling with interparticles and interlayers. The proposed SERS platform showed an enhancement factor of 1.1 × 10(9), high reproducibility (relative standard deviation of 4.2%), and 10(-12) M rhodamine B highly sensitive detection limit by optimizing the SILAR conditions including the concentration of the reactive solution (20/20 mM/mM AgNO3/NaBH4) and the number of SILAR cycles (six). The applicability of the SERS platform was evaluated using two samples including human cervical fluid for clinical diagnosis of human papillomavirus (HPV) infection, associated with cervical cancer, and a malachite green (MG) solution for fungicide and parasiticide in aquaculture, associated with human carcinogenesis. The AgNP-immersed SERS-functionalized platform using the SILAR technique allowed for high chemical structure sensitivity without additional tagging or chemical modification, making it a good alternative for early clinical diagnosis of HPV infection and detection of MG-activated human carcinogenesis.

Room-temperature sensor based on surface-enhanced Raman spectroscopy

As reported in the literature, several factors, such as scattering cross sections, polarisability and wavelength suitability, contribute to increased SERS enhancement. In general, the advantage of surface-enhanced Raman scattering (SERS)-active Ag nanoparticles (NPs) is their higher SERS enhancement over Au NPs because the molar extinction coefficient of the Ag NPs is the highest of its kind among metals. Nevertheless, the corresponding SERS-active hot spots on Au are of inherently greater stability than on Ag. In this work, innovative temperature sensors based on SERS-active Au and Ag substrates prepared by sonoelectrochemical deposition-dissolution cycles (SEDDCs) are first reported. The SERS intensity of the model probe molecules of Rhodamine 6G (R6G) adsorbed on a SERS-active Ag substrate is monotonically increased from 25 to 50 °C. Moreover, this temperature-dependent intensity is linear with a slope of ca. 430 cps per °C between 25 to 45 °C. In addition, the reversibility and reusability of the developed temperature sensors are evaluated after the R6G-adsorbed sensors are alternately exposed to the temperatures of 25 and 45 °C in a sealed chamber. After every five cycles, the SERS spectra of treated substrates were recorded and compared with those of the as-prepared substrates. Experimental results indicate that SERS enhancement capability is mostly reversible based on 90% intensity of the Raman signal being maintained for the SERS-active Au substrate after 25 cycles (only 15 cycles for the Ag substrate).