We developed an optoacoustic biosensor intended for the detection of bloodborne microorganisms using immunoaffinity reactions of antibody-coupled gold nanorods as contrast agents specifically targeted to the antigen of interest. Optoacoustic responses generated by the samples are detected using a wide band ultrasonic transducer. The sensitivity of the technique has been assessed by determining minimally detectable optical density which corresponds to the minimum detectable concentration of the target viral surface antigens. Both ionic solutions and gold nanorods served as the contrast agent generating the optoacoustic response. The sensitivity of Nano-LISA is at least OD=10 -6 which allows reliable detection of 1 pg/ml (depending on the commercial antibodies that are used). Adequate detection sensitivity, as well as lack of non-specific cross-reaction between antigens favors NanoLISA as a viable technology for biosensor development.