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In this study, we report a detailed experimental, binding free energy calculation and molecular dynamics (MD) simulation investigation of the interactions of carboxylic-functionalized multi-walled carbon nanotubes (COOH-f-MWCNTs) with porcine trypsin (pTry). The enzyme exhibits decreased thermostability at 330K in the presence of COOH-f-MWCNTs. Furthermore, the activity of pTry also decreases in the presence of COOH-f-MWCNTs. The restricted diffusion of the substrate to the active site of the enzyme was observed in the experiment. The MD simulation analysis suggested that this could be because of the blocking of the S1 pocket of pTry, which plays a vital role in the substrate selectivity. The intrinsic fluorescence of pTry is quenched with increase in the COOH-f-MWCNTs concentration. Circular dichroism (CD) and UV–visible absorption spectroscopies indicate the ability of COOH-f-MWCNTs to experience conformational change in the native structure of the enzyme. The binding free energy calculations also show that electrostatics, π-cation, and π-π stacking interactions play important roles in the binding of the carboxylated CNTs with pTry. The MD simulation results demonstrated that the carboxylated CNTs adsorb to the enzyme stronger than the CNT without the–COOH groups. Our observations can provide an example of the nanoscale toxicity of COOH-f-MWCNTs for proteins, which is a critical issue for in vivo application of COOH-f-MWCNTs. [ABSTRACT FROM AUTHOR]

Common approaches for DNA mutation detection are high cost and have difficult or complex procedure. We propose a fast quantitative method for recognition of DNA mutation based on SWNT/DNA self-assembled nanostructure. Covalent SWNT/DNA hybrid nanostructures are widely used in the fabrication of electrochemical biosensors. Interfacing carbon nanotubes with DNA in particular, is used as a detection method for the analysis of genetic disorders or the detection of mismatches in DNA hybridisation. We have designed a self-assembled, branch-shaped hybrid nanostructure by hybridisation of two sticky oligos that are attached to the ends of SWNTs via a linker oligo. These hybrid nanostructures showed a good conductivity that was greater than free SWNTs. Impedance spectroscopy studies illustrated that the conductivity of these hybrid nanostructures depended on the conformation and structure of the hybridised DNA. We demonstrated that the strategy of using SWNT/DNA self-assembled hybrid nanostructure fabrication yields sensitive and selective tools to discriminate mismatches in DNA. Cyclic voltammetry (CV) and impedance spectroscopy clearly revealed that the conductivity of the branch-shaped and hierarchical hybridised SWNT/DNA nanostructure is higher when matched, than when mismatched in a 1 and 1′ hybridised SWNT/DNA nanostructure. Rapid biosensing of match and mismatch nanostructure based on carbon printed electrode showed similar results which can be used for rapid and fast detection of DNA mismatch. • We designed a self-assembled, hierarchical branch-shape hybrid nanostructures. • Biophysical and electrochemical properties of self-assembled, hierarchical branch-shape hybrid nanostructures is studied. • Conductivity of these hybrid nanostructures depends on conformation and structure of the hybridised DNA. • SWNT/DNA self-assembled hybrid nanostructure is used as sensitive and selective tool to discriminate mismatches in DNA. • Conductivity of the branch-shaped and matched hybridised SWNT/DNA nanostructure is higher than mismatched one. [ABSTRACT FROM AUTHOR]