Detection of gold-nanorod targeted pathogens using optical and piezoelectric optoacoustic sensors: Comparative study Andre Conjusteau a , Saher Maswadi b, Sergey Ermilov a , Hans-Peter Brecht a , Norman Barsalou c , Randolph D. Glickman b , and Alexander A. Oraevsky a* a Fairway Medical Technologies, Houston, TX b Department of Ophthalmology, University of Texas Health Science Center, San Antonio, TX c Naval Health Research Center Detachment, Brooks City-Base, San Antonio, TX ABSTRACT We demonstrated the ability to detect surface antigens, associated with pathogens, utilizing laser optoacoustic spectroscopy with antibody-coupled gold nanorods (GNR) as a contrast agent specifically targeted to the antigen of interest. The sensitivity of the technique has been assessed by determining the minimum detectable concentration of a surface antigen from biological samples. We compared the sensitivity and applicability of two different methods for detecting optoacoustic responses, using either optical or piezoelectric sensors. Biological samples were adsorbed to the inside walls of detachable, flat-bottomed plastic micro-wells, and then probed with appropriate antibodies conjugated with gold nanorods. If the target antigens were present, the antibody-nanoparticle conjugates were bound, while any nonadsorbed nanoparticles were washed out of the wells. Optoacoustic signals were generated from the bound nanorods using a pulsed pump laser at wavelengths corresponding to one of the peak absorptions of the nanorods. Optoacoustic responses were obtained from the samples using both detection modalities. The sensitivity, suitability, ease of use of each method were assessed and compared. Initial results indicate that optical detection gives comparable sensitivity as the piezoelectric method, and further enhancement of the detection sensitivity is possible for both methods. An advantage of the piezoelectric detection method is that it may be implemented in a more compact assembly, compared to the optical method, however, the optical method may be less sensitive to external electromagnetic and acoustic noise. Further evaluation will be required to refine these measurements. The results with both methods indicate that the use of antibody-targeted nanorod contrast agents, with laser-optoacoustic detection, is a promising technology for the development of rapid in vitro diagnostic tests. Keywords: pathogenic detection, optoacoustic, gold nanoparticles, piezoelectric, probe beam deflection technique 1. INTRODUCTION Combination of optoacoustic detection methods, known for their high sensitivity, with contrast agents based on metal nanoparticles that possess strong optical absorption and effective conversion of the optical energy into heat promises to bring about a large number of biomedical applications [1]. These applications include imaging [2], sensing [3] and monitoring of targeted therapy [4, 5]. Optoacoustic detection of very small concentration of cells, bacteria or other micro-organisms may open doors for an effective early diagnostics of deceases [6, 7]. An essential aspect of the application of optoacoustic techniques to biomedical problems is the optimization of the methods used for recording the acoustic responses induced in the biological target, such as pathological microorganism (PMO). Most researchers in this field utilize acoustically coupled piezoelectric transducers (ultrasonic hydrophones) for this purpose, directly detecting laser-induced pressure transients. It is also possible to detect these signals optically, exploiting either (etalon) interferometry [8] or a technique based on the change in refractive index induced in the sample medium due to propagation of the pressure waves [7, 9-11]. In the present study, the technical aspects of detecting optoacoustic signals by an ultrawide-band ultrasonic transducer were compared with the transient pressure measurement using optical beam deflection method. The ultimate goal of our study is to develop an optoacoustic biosensor for blood Photons Plus Ultrasound: Imaging and Sensing 2009, edited by Alexander A. Oraevsky, Lihong V. Wang, Proc. of SPIE Vol. 7177, 71771P · © 2009 SPIE · CCC code: 1605-7422/09/$18 · doi: 10.1117/12.813434 Proc. of SPIE Vol. 7177 71771P-1