Aptamer-based biosensor for targeting biomarkers in the digestive tract fluids

Lately, ingestible capsules that can be customized for endoscopy have been developed. Such capsules, traveling through the gastrointestinal (GI) tract can be integrated with biosensors for rapid detection of biomarkers of different diseases, e.g., irritable bowel syndrome, malabsorption of carbohydrates and different types of cancers. The advantages of such systems are high sensitivity, known localization of the detected lesion, and being patient friendly. Yet, a biosensor that will function in vivo under the harsh conditions of the GI tract should be label-free, highly specific towards its target within the complex GI fluids, and requires no sample preparation and washing steps.

We have developed a label-free optical biosensor based on nanostructured porous silicon (PSi) Fabry-Pérot thin films. The PSi is used as optical transducer element, and is conjugated with an aptamer as a capture probe. Aptamers are single-stranded oligonucleotides, widely used as recognition elements, due to their specificity, high binding affinity and outstanding stability. Exposure of the aptamer-conjugated PSi to its target analyte changes the optical reflectivity spectrum and is assigned to specific aptamer-target binding events. The biosensor was optimized to allow continuous and selective monitoring of the model protein in real GI fluids by proper passivation of its surface. The optical response of the aptamer-conjugated PSi was tested upon exposure to real GI fluids spiked with the target protein. The performance of the biosensor (its sensitivity and selectivity) was characterized under different simulated flow conditions. The optimized biosensor exhibits reproducible, selective and real time detection of target protein in concentrations >10 µM in real GI fluids. Such biosensors can be implemented within swallowable capsule devices and used for detection of biomarkers in the GI tract.