This Small Business Technology Transfer Phase I project will develop a new type of nanostructured substrate for applications in arsenide detection using surface enhanced Raman spectroscopy (SERS). Arsenic is a well known toxic chemical which exists in both nature and industrial processes, and its detection and monitoring at very low concentration is highly desired. SERS, which relies on Raman signal enhancements for molecules in close contact with noble metal nanostructures, can provide essential information for detection and identification of biological and chemical materials including arsenic. However, its application has been obstructed primarily by the lack of SERS substrates that can be fabricated with high performance and in a repeatable fashion. The proposed research aims to resolve this issue by developing SERS substrates through designing, fabricating, and testing a new nanostructured noble metal substrate.
The broader impact/commercial potential of this project will be high-performance and low-cost SERS substrates that can be employed for monitoring drinking water for chemical toxins such as arsenic and cyanide. Additionally, a large range of SERS-related technologies will benefit from the development of improved design and fabrication processes for plasmonic nanostructures. Success of the project will facilitate large-scale manufacturing of reliable SERS substrates for applications in defense, medical diagnostics, environment monitoring, drug development, forensics and analytical chemistry.
The objective of this Small Business TechnologyTransfer (STTR) Phase I project is to develop substrates of novel plasmonic nanoantennas for application in trace level molecular detections based on surface enhanced Raman spectroscopy (SERS). During the Phase I project period, the designs for optical nanoantennas have been optimized to allow for large-scale reproducible manufacturing with high SERS enhancement factors. The optical properties of the nanoantennas have been investigated through both numerical simulations and experiments as a function of the geometrical parameters and material properties. The simulation results have provided both basic physical understanding and guidance to the device design/fabrications. Fig. 1 presents some representative simulation results about reflectance and local field distributions for the plasmonic nanocavity modes. Substrates with the proposed plasmonic nanoantennas arrays were fabricated using electron beam lithography method combined with thin film depositions and lift-off processes. Representative SEM and optical microscopic pictures are presented in shown in Fig.2. The optical properties of such plasmonic nanoantennas arrays were characterized by measuring optical reflection spectra, which show good agreement with numerical simulations. The Raman enhancements of these plasmonic nanoantennas substrates were characterized by measuring the Raman spectra of 4-Aminothophenol (4-ATP) monolayer self-assembled on the nanoantennas. The measured enhancement factors from our samples achieved 108, which is our Phase I goal. As a demonstration of the commercialization potential of this novel nanoantenna substrates, SERS measurements were performed on our samples and a commercial product sample at the same conditions (sample laser excitation condition, sample measurement system, same incubation time with methanol solutions of ATP). The testing results (shown in Fig.3) show that the SERS signals of our substrates are at least one order of magnitude stronger than that of this commercial SERS substrate. The broader impacts/commercial potential will be that a large range of SERS related technologies will benefit from the improved nanoantenna design and fabrication. Success of commercialization of the technology developed in this project will enable a high performance and low cost SERS substrates that have a significant market opportunity in food safety assurance, medical diagnostic, environment monitoring, pharmaceutical drug development, forensics and analytical Chemistry, and military and homeland security. High sensitive SERS substrates are highly desired for applications including detection of harmful adulteration and pollution in food samples, rapid analysis and quantification of the illegal drug concentration in urine samples for emergency room, and non-invasive bovine embryo viability assessment through SERS detection of embryo metabolites in spent culture medium. High sensitive SERS substrates also are used for detection of explosives, chemical weapons, whole pathogens, and bacteria in water and vapor, for ensure military and homeland security. In environment monitoring, the proposed SERS substrates show promise for the monitoring of drinking water for chemical agents and other toxic chemicals such as arsenic and cyanide.
