Molecular conductance of double-stranded DNA evaluated by electrochemical capacitance spectroscopy

On the fundamentals of quantum rate theory and the long-range electron transport in respiratory chains

It has been shown that both the electron-transfer rate constant of an electrochemical reaction and the conductance quantum are correlated with the concept of quantum capacitance. This simple association between the two separate concepts has an entirely quantum rate basis that encompasses the electron-transfer rate theory as originally proposed by Rudolph A. Marcus whether statistical mechanics is appropriately taken into account. I have prepared a concise review of the quantum mechanical rate theory principles focused on its quantum electrodynamics character to demonstrate that it can reconcile the conflicting views established on attempting to use the super-exchange (supported on electron transfer) or 'metallic-like' (supported on conductance quantum) mechanisms separately to explain the highly efficient long-range electron transport observed in the respiratory processes of living cells. The unresolved issues related to long-range electron transport are clarified in light of the quantum rate theory with a discussion focused on Geobacter sulfurreducens films as a reference standard of the respiration chain. Theoretical analyses supported by experimental data suggest that the efficiency of respiration within a long-range electron transport path is intrinsically a quantum mechanical event that follows relativistic quantum electrodynamics principles as addressed by quantum rate theory.

Introducing Nanoscale Electrochemistry in Small-Molecule Detection for Tackling Existing Limitations of Affinity-Based Label-Free Biosensing Applications

Electrochemical sensing techniques for small molecules have progressed in many applications, including disease diagnosis and prevention as well as monitoring of health conditions. However, affinity-based detection for low-abundance small molecules is still challenging due to the imbalance in target-to-receptor size ratio as well as the lack of a highly sensitive signal transducing method. Herein, we introduced nanoscale electrochemistry in affinity-based small molecule detection by measuring the change of quantum electrochemical properties with a nanoscale artificial receptor upon binding. We prepared a nanoscale molecularly imprinted composite polymer (MICP) for cortisol by electrochemically copolymerizing β-cyclodextrin and redox-active methylene blue to offer a high target-to-receptor size ratio, thus realizing "bind-and-read" detection of cortisol as a representative target small molecule, along with extremely high sensitivity. Using the quantum conductance measurement, the present MICP-based sensor can detect cortisol from 1.00 × 10-12 to 1.00 × 10-6 M with a detection limit of 3.93 × 10-13 M (S/N = 3), which is much lower than those obtained with other electrochemical methods. Moreover, the present MICP-based cortisol sensor exhibited reversible cortisol sensing capability through a simple electrochemical regeneration process without cumbersome steps of washing and solution change, which enables "continuous detection". In situ detection of cortisol in human saliva following circadian rhythm was carried out with the present MICP-based cortisol sensor, and the results were validated with the LC-MS/MS method. Consequently, this present cortisol sensor based on nanoscale MICP and quantum electrochemistry overcomes the limitations of affinity-based biosensors, opening up new possibilities for sensor applications in point-of-care and wearable healthcare devices.

Electron transfer and conductance quantum

The electron transfer rate constant of an electrochemical reaction and the conductance quantum are fundamental concepts that drive processes ranging from nanoscale electronic circuits to photosynthesis. In this paper, it is demonstrated that they are correlated with the concept of electrochemical capacitance. The relationship between electron transfer rate, quantum transport and electrochemical capacitance encompasses the theory of electron transfer rate proposed by Rudolph A. Marcus, and potentially unites electronics and electrochemistry.

Introducing mesoscopic charge transfer rates into molecular electronics

It has been demonstrated that the concept of mesoscopic rate is able to establish a bridge between electrochemical and molecular electronic concepts.

Mesoscopic behaviour of multi-layered graphene: the meaning of supercapacitance revisited

The double layer capacitive phenomena is just a particular case of a more general quantum mechanical approach, wherein the electrochemical capacitance is central hence governing the super-capacitance phenomenology in general.