SERS-Based Microfluidic Sensors for Trace Analysis of Hazardous Materials

Abstract

Surface-enhanced Raman scattering (SERS) is a powerful highly sensitive analytical method for a range of applications where high sensitivity needs to be combined with good discrimination between molecular targets due to their unique vibrational characteristics. When target molecules are adsorbed onto roughened metal surfaces, the associated SERS signals are greatly increased due to electromagnetic and chemical enhancements at SERS active sites known as “hot spots” upon exposure to an excitation laser source. This enhancement shows promise in overcoming the low sensitivity problem inherent in conventional Raman, fluorescence, and electrochemical detection. In this work, SERS was used as a highly sensitive detection technology on microfluidic chip. Microfluidics, which manipulate and analyze small volumes of fluids has emerged as a powerful technology with many established and relevant applications such as chemistry, biochemistry, nanotechnology, physics and biotechnology. Microfluidics improve the efficiency of procedures by increasing mass transfer and tremendously reducing sample consumption. The advantages of microfluidics have leaded to many innovative technologies in optical analysis. Combining SERS with microfluidics allows for the sensitive monitoring, detection and analysis of many kinds of samples in microfluidic environments. This work mainly focused on the development of this combining technology, which was called SERS-based microfluidic sensor. Hazardous materials greatly threaten environmental security and human health because human exposure to their toxic chemical ingredients may lead to serious injury or death. These dangerous materials are used in many manufacturing factories. They include heavy metal ions (Hg2+, Cd2+, As3+, Pb2+, etc.), toxic gases (SO2, NOx, HCl, etc.), pesticides, chemical and biological warfare agents (anthrax, mustard gas, sarin, etc.) and other hazardous wastes. In particular, biologically hazardous materials have been attracted attention among environmental scientists. In this case, the immunoassay which is a biochemical test based on the specific interaction between antigen and antibody has become an important analytical tool for identifying hazardous targets in solution. Nonetheless, this assay technique has some technical limits such as poor limit of detection long assay time and limited multiplex detection capability. By taking the advantage of SERS-based microfluidic sensor, several microfluidic chips were specially designed and applied for synthesis of nanoparticles and quantitative analysis of various hazardous materials, such as herbicide, cancer marker and anthrax biomarker. It demonstrated an ultra-low detection limit which was enhanced by approximately one to two orders of magnitude compared to conventional analytical methods. This SERS-based microfluidic sensor is expected to be a powerful analytical tool for fast and reproducible trace analysis of various hazardous materials.