Continuous sensing of tumor-targeted molecular probes with a vertical cavity surface emitting laser-based biosensor

Abstract

Abstract. Molecular optical imaging is a widespread technique for interrogating molecular events in living subjects. However, current approaches preclude long-term, continuous measurements in awake, mobile subjects, a strategy crucial in several medical conditions. Consequently, we designed a novel, lightweight miniature biosensor for in vivo continuous optical sensing. The biosensor contains an enclosed vertical-cavity surface-emitting semiconductor laser and an adjacent pair of near-infrared optically filtered detectors. We employed two sensors (dual sensing) to simultaneously interrogate normal and diseased tumor sites. Having established the sensors are precise with phantom and in vivo studies, we performed dual, continuous sensing in tumor (human glioblastoma cells) bearing mice using the targeted molecular probe cRGD-Cy5.5, which targets α V β 3 cell surface integrins in both tumor neovasculature and tumor. The sensors capture the dynamic time-activity curve of the targeted molecular probe. The average tumor to background ratio after signal calibration for cRGD-Cy5.5 injection is approximately 2.43 AE 0.95 at 1 h and 3.64 AE 1.38 at 2 h (N ¼ 5 mice), consistent with data obtained with a cooled charge coupled device camera. We conclude that our novel, portable, precise biosensor can be used to evaluate both kinetics and steady state levels of molecular probes in various disease applications.

Real-time, continuous, fluorescence sensing in a freely-moving subject with an implanted hybrid VCSEL/CMOS biosensor

“…The optoelectronic components have been previously described in detail [6,8,11]. For completeness, we summarize those results here.…”

“…These optical components were separately evaluated and validated in vitro and in vivo in previous studies in a subcutaneous dye model, a phantom model, and a tumor model in which fluorescent molecular probe is injected systemically and accumulates in tumors [6,8]. Using these approaches, we achieved autofluorescence-limited sensitivity to subcutaneous fluorophore in a nude mouse.…”

“…We optimized our hybrid sensor for the detection of Cy5.5 fluorescent dye (Amersham/GE Healthcare), which can be conjugated to molecular binders (small molecules, macromolecules, protein fragments or proteins) to create molecular probes for in vivo studies [8]. The excitation and emission spectra of Cy5.5 lies in the far-red to NIR spectral region, where tissue absorption is relatively minimal and the optical penetration depth can be large compared to other wavelengths [12].…”

“…These approaches, while non-invasive and highly sensitive, limit the ability to perform long-term, continuous measurements greater than several hours because of the inherent requirement to confine the animal subject to a light-tight box. We and others have developed miniature fluorescence-sensing systems that can be directly mounted on, or implanted in, an animal model [4][5][6][7][8][9][10] for continuous molecular monitoring in freely-moving subjects. Although potentially invasive, an implant also allows monitoring of deep tissues which may not be accessible with epi-illumination techniques.…”

“…We have previously reported the fabrication and testing of a miniature, integrated semiconductor fluorescence sensor designed for the detection of Cyanine 5.5 (Cy5.5; GE Healthcare/Amersham)-based far-red / near-infrared (NIR) fluorescent probes [6,8,11]. The sensor incorporated three essential components of a fluorescence system, including a 670nm vertical-cavity surface-emitting laser (VCSEL) excitation source, a Gallium Arsenide (GaAs) p-i-n photodiode, and a fluorescence emission filter.…”