Modeling ion sensing in molecular electronics

Determination of Ag[I] and NADH Using Single-Molecule Conductance Ratiometric Probes

The sensing platform based on single-molecule measurements provides a new perspective for constructing ultrasensitive systems. However, most of these sensing platforms are unavailable for the accurate determination of target analytes. Herein, we demonstrate a conductance ratiometric strategy combing with the single-molecule conductance techniques for ultrasensitive and precise determination. A single-molecule sensing platform was constructed with the 3,3',5,5'-tetramethylbenzidine (TMB) and oxidized TMB (oxTMB) as the conductance ratiometric probes, which was applied in the detection of Ag[I] and nicotinamide adenine dinucleotide (NADH). It was found that the charge transport properties of TMB and oxTMB were distinct with more than an order of magnitude change of the conductance, thus enabling conductance ratiometric analysis of the Ag[I] and NADH in the real samples. The proposed method is ultrasensitive and has an anti-interference ability in the complicated matrix. The limit of detection can be as low as attomolar concentrations (∼34 aM). We believe that the proposed conductance ratiometric approach is generally enough to have a promising potential for broad and complicated analysis.

Chemical sensing with Au and Ag nanoparticles

Noble metal nanoparticles (NPs) are ideal scaffolds for the fabrication of sensing devices because of their high surface-to-volume ratio combined with their unique optical and electrical properties which are extremely sensitive to changes in the environment. Such characteristics guarantee high sensitivity in sensing processes. Metal NPs can be decorated with ad hoc molecular building blocks which can act as receptors of specific analytes. By pursuing this strategy, and by taking full advantage of the specificity of supramolecular recognition events, highly selective sensing devices can be fabricated. Besides, noble metal NPs can also be a pivotal element for the fabrication of chemical nose/tongue sensors to target complex mixtures of analytes. This review highlights the most enlightening strategies developed during the last decade, towards the fabrication of chemical sensors with either optical or electrical readout combining high sensitivity and selectivity, along with fast response and full reversibility, with special attention to approaches that enable efficient environmental and health monitoring.

Four probe electron transport characteristics of porphyrin phenylacetylene molecular devices

A novel functional nano-electronic molecular system by tuning gate voltages and source voltages as well as changing lead-to-lead channels.

Lateral scaling and positioning effects of top-gate electrodes on single-molecule field-effect transistors

Molecular electronics aims at integrating controllable molecular devices into circuits or machines to realize certain functions. According to device configuration, molecular field-effect transistors with top-gate electrodes have great advantages for integration. Nevertheless, from technical aspects, it is difficult to control lateral scale and position of a top-gate electrode precisely. Therefore, one problem arises in how lateral scaling and positioning effects of a top-gate electrode affect device performance. To solve this problem, the electronic transport properties of single-molecule field-effect transistor configurations modulated by a series of partial-scale top-gate electrodes with different lateral scales and positions are studied by using non-equilibrium Green's function in combination with density functional theory, and compared with those of the full gate electrode (can be considered as a bottom gate electrode). The results show that lateral scaling and positioning effects indeed have a great impact on electronic transport properties of single-molecule field-effect transistor configurations. For [Formula: see text]-saturated 1,12-dodecanedithiol devices, larger lateral scale of a partial-scale top-gate electrode obtains larger amplification coefficient [Formula: see text] (ratio of device conductances with/without a gate electrode), and even larger [Formula: see text] than that of the full gate electrode. While lateral positioning effect has little influence on this device. For [Formula: see text]-conjugated 1,3,5,7,9,11-dodehexaene-1,12-dithiol devices, performance of a partial-scale top-gate electrode mainly depends on locations of its two edges, i.e. the number of [Formula: see text] bonds that it breaks. These results will provide theoretical directions in device designing and manufacturing in the future.

Conductance Switching in Single-Peptide Molecules through Interferer Binding

Detection of bioprocess-interfering metal ions and molecules is important for healthcare, and peptide single-molecule junctions have shown their potential toward sensing these targets efficiently. Using first-principles calculations, we investigate the conductance of Cys-Gly-Cys and cysteamine-Gly-Gly-Cys peptide junctions, and the effect of its change upon copper-ion (Cu2+) or bisphenol A (BPA) binding. The calculated conductance of the peptides and the Cu2+-peptide complexes agrees well with the experimental data and that of the BPA-bond peptides is further predicted. Our analyses show that the conductance switching mainly comes from the structure deformation of the peptide caused by Cu2+ binding or from the new conduction channel added by BPA binding. Our results suggest that the cysteamine-Gly-Gly-Cys junction can recognize Cu2+ and BPA better than the Cys-Gly-Cys one does.

Chemical substitution assisted ion sensing with organic molecules: a case study of naphthalene

Using first-principles calculations, we predict that a naphthalene molecule with N substitutions for the –CH groups is a good system for H⁺ sensing.

Ordered nanoparticle arrays interconnected by molecular linkers: electronic and optoelectronic properties

Arrays of metal nanoparticles in an organic matrix have attracted a lot of interest due to their diverse electronic and optoelectronic properties.