Optoacoustic sensing of ocular bacterial antigen using targeted gold nanorods

Abstract

Bacterial contamination can be detected using a minimally invasive optical method, based on laser-induced optoacoustic spectroscopy, to probe for specific antigens associated with a specific infectious agent. As a model system, we have used a surface antigen (Ag), isolated from Chlamydia trachomatis, and a complementary antibody (Ab). A preparation of 0.2 mg/ml of monoclonal Ab specific to the C. trachomatis surface Ag was conjugated to gold nanorods using standard commercial reagents, in order to produce a targeted contrast agent with a strong optoacoustic signal. The C. trachomatis Ag was absorbed in standard plastic microwells, and the binding of the complementary Ab-nanorod conjugate was tested in an immunoaffinity assay. Optoacoustic signals were elicited from the bound nanorods, using an optical parametric oscillator (OPO) laser system as the optical pump. The wavelength tuneability of the OPO optimized the spectroscopic measurement by exciting the nanorods at their optical absorption maxima. Optoacoustic responses were measured in the microwells using a probe beam deflection technique. Immunoaffinity assays were performed on several dilutions of purified C. trachomatis antigen ranging from 50 µg/ml to 1 pg/ml, in order to determine the detection limit for the optoacoustic-based assay. Only when the antigen was present, and the complementary Ab-NR reagent was introduced into the microwell, was an enhanced optoacoustic signal obtained, which indicated specific binding of the Ab-NR complex. The limit of detection with the current system design is between 1 and 5 pg/ml of bacterial Ag.

All-optical optoacoustic microscopy based on probe beam deflection technique

“…The propagation of the pressure wave produces a local density gradient, which alters the refractive index of the coupling medium (in this case DI water) which is directly proportional to pressure (piezo-optic coefficient dn/dP = for water [29] ), leading to beam deflection. PBDT has been extensively described in our previous work [17] , [24] , [25] , [26] , [27] . In short, the sensor beam interacts with a spherical shape pressure wave generated from a point source and the interaction length between the probe beam and the pressure waterfront is limited to a small area or just a point of interaction as illustrated in Fig.…”

“…In this paper, we introduce a novel OAM design that utilizes an all-optical method, the probe beam deflection technique (PBDT), for ultrasound generation and detection [17] , [24] , [25] , [26] , [27] . A recent review of all-optical OAM methods [28] did not mention the PBDT, which emphasizes the novelty of this method in optoacoustic microscopy.…”

Characterization of Pressure Transients Generated by Nanosecond Electrical Pulse (nsEP) Exposure

“…10C ) by a motorized stage capable of moving 25 mm in the X-plane and 12 mm in the Y-plane. When a wave generated from the electrodes intersected the probe beam, the variation in the refractive index of the medium caused the probe beam to deflect from its original direction, which appeared as an intensity and/or trajectory change in the output of the position detector 17 18 19 20 21 22 .…”

“…We hypothesize that pressure transients created by nsEP exposure 17 are directly linked to the phenomena of nanoporation. We used the probe beam deflection technique (PBDT), an all-optical, non-contact method for detecting pressure transients generated in gaseous and liquid environments to characterize the pressure transients generated by typical nsEP expsoures 18 19 20 21 22 . With PBDT, the propagation of a pressure transient causes a change in the refractive index of the medium through which a probe beam travels, resulting in a deflection of that beam.…”

PEG-coated gold nanorod monoclonal antibody conjugates in preclinical research with optoacoustic tomography, photothermal therapy, and sensing

“…We have previously reported on the development of 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 [30][31][32] . 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).…”