Novel Nanobiosensing Using a Focused Laser Beam

Abstract

Lasers are very useful in nanobiosensing. The laser beam is spatially coherent and can be tightly focused by lenses. Interactions of photons with matter in the laser focus enable micro- and nanoscale analyses of a small objective in a specific area. In addition, focusing a laser beam induces photochemical reactions and optical forces in a sub-micron region of molecular solutions and nanoparticle dispersions. These effects of a focused laser beam are utilized for developing rapid, sensitive, compact, and low-cost biosensors, which are required for applications in point-of-care diagnostics, food safety controls, and environmental monitoring. In the first part of this chapter, a biosensing technique is introduced which works by simply focusing a single laser beam and detecting its reflection intensity. The polymer nanostructure deposited in a laser focus due to self-catalytic oxidative photopolymerization converts the enzyme reactions of horseradish peroxidase into a back-reflected intensity of the focused laser beam. A reliable optical quantification of glucose can be performed in a short time on a small sample volume. Another biosensing technique based on optical trapping of Ag nanoparticles is effective for sensitive biomolecular detection in solution. A focused laser beam immobilizes Ag nanoparticles with analyte molecules at a local spot on a polymer substrate. Surface-enhanced Raman scattering of analyte molecules can be measured by irradiation of a visible-light excitation laser beam. Adenine molecules are detected quantitatively in a concentration range from 0.01 to 1 μM.