We report a novel optical biosensor platform using near-infrared (NIR) fluorescent single-walled carbon nanotubes (SWNTs) functionalized with target-recognizing aptamer DNA for noninvasively detecting cell signaling molecules in real-time. Photoluminescence (PL) emission of aptamer-coated SWNTs is modulated upon selectively binding to target molecules, which is exploited to detect insulin using an insulin-binding aptamer (IBA) as a molecular recognition element. We find that nanotube PL quenches upon insulin recognition via a photoinduced charge transfer mechanism with a quenching rate of kq = 5.85×1014 M−1s−1 and a diffusion-reaction rate of kr = 0.129 s−1. Circular dichroism spectra reveal for the first time that IBA strands retain a four-stranded, parallel guanine quadruplex conformation on the nanotubes, ensuring target selectivity. We demonstrate that these IBA-functionalized SWNT sensors incorporated in a collagen extracellular matrix (ECM) can be regenerated by removing bound analytes through enzymatic proteolysis. As proof-of-concept, we show that the SWNT sensors embedded in the ECM promptly detect insulin secreted by cultured pancreatic INS-1 cells stimulated by glucose influx and report a gradient contour of insulin secretion profile. This novel design enables new types of label-free assays and non-invasive, in-situ, real-time detection schemes for cell signaling molecules.

Light harvesting nanostructure hybrids have been designed and demonstrated using single-wall carbon nanotubes (SWCNTs) and porphyrin chromophores. DNA oligonucleotides are used to conjugate SWCNTs with light-absorbing chromophores for transparent films which generate photocurrents. High-purity semiconducting SWCNTs demonstrate significant enhancement in the photocurrent compared to metallic or unsorted tubes.

DNA-coated individual single-walled carbon nanotubes (SWNTs) attract research attention as bio-sensors because they have unique optical properties of discrete near-infrared fluorescence. The optical characteristics of SWNTs are attributed to the one-dimensional quantum confinement which also renders SWNTs extremely sensitive to environmental changes. In this work, we investigated optical modulation of DNA-coated SWNTs upon binding to target molecules, and explored the observed phenomena for biomolecular sensing applications. We used insulin-binding aptamer to recognize a molecular target (insulin) with high specificity and sensitivity, by forming a unique secondary structure of guanine quadruplex. We also examined SWNT interactions with insulin based on optical transduction using a novel single SWNT spectroscopy. Based on the quenching of insuiln-binding aptamer-coated SWNT photoluminescence with insulin, we developed the simple biosensor for detection of insulin.

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