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L. Woodward, S. Maswadi, R. D. Glickman, A. Oraevsky, N. Barsalou, G. Zhong; Potential for Detecting Ocular Bacterial Antigen Using Photoacoustic Spectroscopy. Invest. Ophthalmol. Vis. Sci. 2007;48(13):4247.
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© ARVO (1962-2015); The Authors (2016-present)
We are investigating the feasibility of detecting ocular bacterial antigen using a minimally invasive optical method based on photoacoustic spectroscopy (PAS). The key technology for implementation of this technique is the utilization of antibody-coupled nanorods as a contrast agent specifically targeted to the antigen of interest.
A preparation of 1mg/ml of monoclonal antibody (Ab) specific to C. trachomatis surface antigen (Ag) was conjugated to gold nanorods using standard commercial reagents, in order to produce a targeted contrast agent with a strong photoacoustic signal. The complementary, C. trachomatis surface Ag was adsorbed to the inside walls of plastic spectrophotometer cuvettes to evaluate the binding of the contrast agents in a modified ELISA. Photoacoustic signals were elicited from the bound nanorods, using an optical parametric oscillator (OPO) laser system as the pump. The short pulses (5-10ns) of the OPO increased efficiency of photoacoustic conversion, while the wavelength tuneability of the OPO optimized the spectroscopic measurement by exciting the nanorods at their optical absorption maxima. PAS responses were measured in the cuvettes, containing the Ab-nanorod-Ag complexes, using a probe beam deflection technique, by directing a low-power HeNe laser beam through the optical surfaces of the cuvette and measuring the beam deflection produced by photoacoustic responses.
The photoacoustic spectrum and the conventional optical absorption spectrum of the solution of C. trachomatis antigen bound to the Ab-conjugated nanorods were found to have absorption peaks at ~750nm, which is consistent with the presence of nanorod contrast agent bound on the cuvette walls.
These findings indicate that targeted contrast agents can enhance the photoacoustic response of specific biomolecules. Although work is ongoing to optimize the reaction conditions, and to determine the specificity of this method by challenging the binding of contrast agent with non-specific Ab, the present observations indicate that PAS with specific contrast enhancement is a promising method for in vivo applications, such as detection of bacterial antigens.
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