Electrochemical Impedance Spectroscopy for Assessing the Recognition of Cytochrome c by Immobilized Calixarenes

Fabrication of a label-free electrochemical aptasensor to detect cytochrome c in the early stage of cell apoptosis

A label-free direct electrochemical aptasensor is presented for the identification of cytochrome c (Cyt c) at the nM concentration level. Carbon nanofibers (CNF), as a highly conductive material, were used to modify a glassy carbon electrode (GCE) and thus increase its conductivity. Moreover, to enhance the immobilization of aptamers (Apt) on the electrode surface, graphene oxide functionalized with aspartic acid (GOAsp) was added to the surface. Aspartic acid with countless carboxyl groups (-COOH) on its surface caused more aptamers to be immobilized on the electrode surface. Electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and differential pulse voltammetry (DPV) were used to monitor the step-by-step fabrication of the label-free direct electrochemical aptasensor. The label-free quantification of Cyt c was also done by the direct electron transfer between the Fe(III)/Fe(II)-heme redox-active sites which were selectively bound to the aptamers on the GCE and the surface of the electrode. Under optimum conditions, the peak currents of differential pulse voltammograms at 0.26 V (vs. Ag/AgCl) were used for calibration. The proposed aptasensor performs in a wide dynamic range from 10 nM to 100 µM with a low detection limit of 0.74 nM for cytochrome c. It also has high selectivity as well as acceptable stability. These advantages make the biosensor capable of detecting early-stage apoptotic cells that contribute to early cancer diagnosis.

Cellular-membrane inspired surface modification of well aligned ZnO nanorods for chemosensing of epinephrine

Modified ZnO nanorods array to form a chemical sensor for neurotransmitters. The interspaces between the nanorods offer highly efficient immobilization of the lipid membrane containing the calixarene, which act as receptor molecule.

Langmuir monolayers and thin films of amphifilic thiacalix[4]arenes. Properties and matrix for the immobilization of cytochrome c

Formation and properties of Langmuir films of thiacalix[4]arene (TCA) derivatives containing N-donor groups on the lower rim (Y═O(CH2)3CN; OCH2CN; NH2; OCH2ArCN-p) in 1,3-alternate conformation on aqueous subphase and solid substrates have been studied. Only tetra-cyanopropoxy-p-tert-butylthiacalix[4]arene 1 forms a typical monomolecular layer with perpendicular orientation of the macrocycle relative to the water-air interface that is able to immobilize cytochrome c in the entire range of the surface pressure. Obtained monolayers were transferred by Langmuir-Schaefer technique onto quartz, indium-tin oxide (ITO), and silicon. It was demonstrated that protein activity is retained after immobilization on the substrate.

Selective and sensitive detection of intracellular O2(•-) using Au NPs/cytochrome c as SERS nanosensors

A novel surface-enhanced Raman scattering (SERS) nanosensor was developed by modifying oxidized cytochrome c (Cyt c) on gold nanoparticles (Au NPs) for the sensitive and selective determination of intracellular superoxide anion radical (O2(•-)). On the basis of the differences in the SERS spectra between the oxidized and reduced form of Cyt c, this nanosensor could be employed to investigate O2(•-) concentration by measuring the SERS spectra of the reduced Cyt c. Using this SERS nanosensor, a detection limit of 1.0 × 10(-8) M for O2(•-) could be attained. Additionally, the selectivity of the SERS nanosensor for O2(•-) was examined, showing that other reactive oxygen species (ROS) and biologically relevant species did not influence the detection of O2(•-). More importantly, the nanosensor could be delivered to the living HeLa and normal human liver cells and permitted the concentration of O2(•-) to be monitored in real time and in a noninvasive manner, which indicates that this nanosensor will be suitable for the qualitative and quantitative analysis of O2(•-) in biosystems, thus leading to a greater understanding of oxidative-stress-related diseases at a cellular level.