Insulin Detection Using a Corona Phase Molecular Recognition Site on Single-Walled Carbon Nanotubes

Abstract

Corona phase molecular recognition (CoPhMoRe) is a technique whereby an external, adsorbed phase around a colloidal nanoparticle is selected such that its molecular conformation or interaction recognizes a specific target analyte. In this work, we employ a high-throughput screening of a library of poly(ethylene glycol) (PEG)-conjugated lipids adsorbed onto near-infrared fluorescent single-walled carbon nanotubes to discover a corona phase selective for insulin. We find that a C-PEG(2000 Da)-ceramide causes a 62% fluorescent intensity decrease of the (10,2) chirality nanotube in the presence of 20 μg/mL insulin. The insulin protein has no prior affinity toward the C-PEG(2000 Da)-ceramide molecules in free solution, verified by isothermal titration calorimetry, and the interaction occurs only upon their adsorption onto the single-walled carbon nanotube scaffolds. Testing a panel of proteins originating from human blood as well as short 7 amino acid fragments of the insulin peptide rules out nonselective recognition mechanisms such as molecular weight, isoelectric point, and hydrophobicity-based detection. Interestingly, longer fragments of isolated α- and β-peptide chains of insulin are detected by the construct, albeit with lower affinity compared to that of the intact insulin protein, suggesting that the construct recognizes insulin in its native form and conformation. Finally, the insulin recognition and the quantification of its solution concentration were demonstrated both in buffer and in blood serum, showing that the CoPhMoRe construct works in this complex environment despite the presence of potential nonspecific adsorption. Our results further motivate the search for nonbiological synthetic recognition sites and open up a new path for continuous insulin monitoring in vivo with the hope of improving glycemic control in closed-loop artificial pancreas systems.

Covalent Surface Modification Effects on Single‐Walled Carbon Nanotubes for Targeted Sensing and Optical Imaging

“…Specifically, when noncovalently adsorbed to the SWCNT surface, single‐stranded DNA (ssDNA) oligomers (GT) 15 and (GT) 6 form known nanosensors for dopamine, [ 14,31 ] DPPE‐PEG5K phospholipid for fibrinogen, [ 17 ] and C 16 ‐PEG2k‐ceramide phospholipid for insulin. [ 18 ] To generate each nanosensor, we induced noncovalent association of the SWCNTs with each coating through π–π aromatic stabilization and hydrophobic packing via probe‐tip sonication or dialysis as previously established (see Section 4 for details). We prepared dopamine, fibrinogen, and insulin nanosensors with both pristine and functionalized SWCNTs.…”

“…Fluorescence spectra were compared between the covalently functionalized SWCNTs as previously reported for each nanosensor. [ 14,17,18,42 ] Briefly, for (GT) 15 ‐SWCNT and (GT) 6 ‐SWCNT nanosensors, the change was compared in the (7,6) chirality peak at 1122 nm. For DPPE‐PEG5k nanosensors, the change in intensity of the joint (9,4) and (7,6) chirality peaks at 1118 nm was compared.…”

“…[ 13 ] This fluorescence has been employed to develop a class of nanosensors that undergo fluorescence modulation upon selective binding of bioanalytes such as neurotransmitters, reactive nitrogen species, metabolites, peptides, and proteins. [ 14–19 ] The selectivity of these varied SWCNT nanosensors is created through a phenomenon termed corona phase molecular recognition (CoPhMoRe). CoPhMoRe nanosensors are capable of binding specific analytes through a constrained surface‐adsorbed state formed by the noncovalent association of the SWCNT surface and a coating, such as polymer or phospholipid, not necessarily known to bind the analyte of interest.…”

Covalent Surface Modification Effects on Single-Walled Carbon Nanotubes for Multimodal Optical Applications

“…Specifically, when noncovalently adsorbed to the surface of SWCNT, DNA oligomers (GT)15 and (GT)6 form known nanosensors for dopamine 13,27 , DPPE-PEG5K phospholipid for fibrinogen, and C16-PEG2k-Ceramide phospholipid for insulin. 17,28 To generate each nanosensor, we induced noncovalent association of the SWCNTs with each coating through π-π aromatic stabilization and hydrophobic packing using probe-tip sonication or dialysis as previously established (see methods for more details).…”

Fluorescent Single-Walled Carbon Nanotubes for Protein Detection

“…The conformation of the amphiphilic polymer, that is, the corona phase, can enable the binding of a specific analyte, resulting in spectral modulations (Figure 3c). In order to discover new corona phases for molecular recognition, a library of polymer-conjugated SWCNT is screened against a panel of analyses, and the nIR fluorescence emission is monitored for intensity changes or wavelength shifts [89,119,129,130]. A successful screen results in a corona phase that can specifically and selectively recognize a target Satishkumar et al [125] used fluorescent SWCNT sensors for the detection of avidin by conjugating redox-active dyes bound to a recognition element, biotin, to the SWCNT surface.…”