Part-Per-Billion Level Chemical Sensing with a Gold-Based SERS-Active Substrate

Abstract

We used surface-enhanced Raman spectroscopy (SERS) for the rapid and sensitive detection and quantification of caffeine in solution. Such a technique incorporated into a portable device is finding wide applications in trace chemical analysis in various fields, including law enforcement, medicine, environmental monitoring, and food quality control. To realize such applications, we are currently developing portable and handheld trace chemical analyzers based on SERS, which are integrated with a sensor embedded with activated gold nanoparticles in a porous glass matrix. In this study, we used this gold SERS-active substrate to measure aqueous solutions of the drug caffeine as a test chemical to benchmark sensor performance by defining sensitivity (lowest measured concentration (LMC) and estimated limit of detection (LOD)), determining concentration dependence and quantification capabilities by constructing calibration curves; by evaluating the effects of pH values of 3, 7, and 11; and by examining the reproducibility of the SERS measurements. The results demonstrate that the SERS sensor is sensitive, with caffeine detected at an LMC of 50 parts per billion (ppb) with an LOD of 0.63 ppb. The results further show that the sensor is very stable and can be used to make reproducible measurements, even under extremely acidic to basic pH conditions. Vibrational assignments of all observed SERS peaks are made and reported for the first time for caffeine on a gold substrate.

Evaluation of the SERS performances of Tabun and VX label-free detection in complex and multicomponent fluids

“…As evident in Fig. 3 c–a major peak appears in the spectrum at 1032 cm −1 , which can be assigned to the in-plane C–C deformation [ 43 ] of caffeine [ 37 ]. Caffeine has indeed been reported as having a high affinity for Au and Ag SERS substrates [ 43 ] and is therefore expected to highly compete with GA for adsorption on the SERS substrate.…”

“…3 c–a major peak appears in the spectrum at 1032 cm −1 , which can be assigned to the in-plane C–C deformation [ 43 ] of caffeine [ 37 ]. Caffeine has indeed been reported as having a high affinity for Au and Ag SERS substrates [ 43 ] and is therefore expected to highly compete with GA for adsorption on the SERS substrate. In addition, the eye serum was much more viscous than the lens solution, due to the presence of many polymers in its formulation, which could in turn form a thicker deposit on the SERS substrate and hinder SERS detection.…”

Rapid Detection of Accelerants in Fire Debris Using a Field Portable Mid-Infrared Quantum Cascade Laser Based Analyzer

“…The algorithm used here to match spectra stored in the library has been discussed in a previously published paper [17]. The estimated limit of detection (LOD) was calculated by a simple approach (following ICH guidelines) based on the signal-to-noise ratio of 3, where LOD = (C)/([S/N]/3), C is the concentration in parts-per-million (ppm) or parts-per-billion (ppb), S is the signal baselinecorrected peak intensity, N is root mean square (RMS) noise, and where the cut-off peak signal is assigned as three times the background-signal or blank [18].…”

From the lab to the field: handheld surface enhanced Raman spectroscopy (SERS) detection of viral proteins

“…6 Many SERS-based sensors have been designed to be compatible with handheld Raman spectrometers, demonstrating detection of viruses, drugs, disease biomarkers, and other targets. [7][8][9][10][11][12][13][14][15][16][17][18] However, there are several known challenges associated with adapting SERS based assays to the point of care. 1 When using a fluorescent Raman reporter probe, fluorescence from the laser excitation can impact the resolution of the acquired spectra.…”