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

Tingting Zhang,Junchang Pei,Frank Inscore,Liyun Wu,Haowen Li,Xuefeng Li

doi:10.3390/s22051778

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.

Highlights

Surface-enhanced Raman spectroscopy (SERS) has become a very powerful optical technique and analytical tool that is finding wide use in a variety of application areas [1,2,3,4,5,6,7].This surge in use can be attributed to the extreme high molecular specificity and sensitivity this technique affords, with single-molecule detection being possible [8,9]
The shifting of plasmon absorption afforded by the extended aggregates of Ag or Au nanoparticles embedded in the sol–gel makes this sensor useful in laser excitation from 532 to 1064 nm, and it is ideal for use with our portable 785 nm Raman system
Assignments bands observed in the normal Raman (NR) and SERS

Summary

Introduction

Surface-enhanced Raman spectroscopy (SERS) has become a very powerful optical technique and analytical tool that is finding wide use in a variety of application areas [1,2,3,4,5,6,7]. This surge in use can be attributed to the extreme high molecular specificity and sensitivity this technique affords, with single-molecule detection being possible [8,9]. The drug caffeine was selected as a probe molecule to evaluate this sensor, as it generates a strong SERS response at 785 nm

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Conclusion