There is currently a great interest in creating extremely sensitive and specific chemical and biological nanosensors. In this regard, the interaction between biological, organic and inorganic materials surface is one of the key issues in the near future. Since the technology must interact with the biological world on the molecular and cellular scale, the structure and properties of that interface must be designed and controlled on that scale. The nanoscale properties of the interface between biological and physical systems are the thematic area common to a huge diversity of devices.
The use of an extremely sensitive technique like Surface-enhanced Raman spectroscopy (SERS) to study organic-inorganic interconnections, including interfacing to biological systems, permits to investigate the role of interfaces in hybrid electrical devices and sensors. The SERS spectroscopy is a very sensitive technique that employs rough substrates with structures in the nanometer range to enhance the Raman signal produced by adsorbed and immobilized species. This signal is too weak to be detected with the conventional Raman spectroscopy. In SERS spectroscopy the effective Raman cross-section can be increased by many orders of magnitude. Therefore, this technique combines the ultra sensitive detection limits with the detailed structural information content of Raman spectroscopy. This spectroscopy has as number of important advantages: sensitivity, selectivity, non-destructive detection, and feasibility for in-situ studies. Besides, it enables the determination of detailed information about adsorbed species like their molecular structure and orientation.
Our research interest is to use and develop SERS spectroscopy to study biologically-inspired systems in which nanostructures play an important role, with a focus on integration of biological component into functional materials. We obtained important results:
a) first observation of molecules adsorbed on semiconductor quantum-dots. We observed the SERS spectrum from pyridine molecules adsorbed on InAs/GaAs quantum dots. The most interesting feature in the SERS spectrum is the appearance of a new vibrational band attributed to the chemisorbed pyridine that is formed on the semiconductor surface;
b) we directly probed the adsorption of biological molecules on MBE-grown II-VI quantum dots. In particular, we detected tyrosine, adenine, and tryptophan molecules adsorbed at a very low concentration on self-assembled CdSe/CdZnSeMg quantum dots;
c) we studied the immobilization of an enzyme in an electrochemical biosensor. This biosensor is a gold nanotubes-based biosensor formed by nanoscopic gold tubes, aligned parallel to each other and presenting uniform size and shape, as electrode and an immobilized glucose oxidase.
These studies showed that SERS technique can provide a useful and versatile technique to understand and control the role of interfaces in nano-systems. Such knowledge, aside from its basic interest, is of great value for device optimization. The integration of biological components into devices and materials is a major frontier in nanotechnology.
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