A single-molecule electrical approach for amino acid detection and chirality recognition

Abstract

One of the ultimate goals of analytic chemistry is to efficiently discriminate between amino acids. Here we demonstrate this ability using a single-molecule electrical methodology based on molecular nanocircuits formed from stable graphene-molecule-graphene single-molecule junctions. These molecular junctions are fabricated by covalently bonding a molecular machine featuring a permethylated-β-cyclodextrin between a pair of graphene point contacts. Using pH to vary the type and charge of the amino acids, we find distinct multimodal current fluctuations originating from the different host-guest interactions, consistent with theoretical calculations. These conductance data produce characteristic dwell times and shuttling rates for each amino acid, and allow accurate, statistical real-time, in situ measurements. Testing four amino acids and their enantiomers shows the ability to distinguish between them within a few microseconds, thus paving a facile and precise way to amino acid identification and even single-molecule protein sequencing.

Capturing the Rotation of One Molecular Crank by Single-Molecule Conductance

“…The measurement of single-molecule conductance in a suspended molecular junction at room temperature provides a direct observation of the in situ conductance change with the conformation flipping. ,, Under a data acquisition rate of 20 000 points per second, the gold tip was suspended during the retraction process for more than 150 ms after the retraction distance being suitable for the formation of molecular junctions. The conductance-time traces as much as 2624, 2599, and 2577 for compounds 1 – 3 were recorded, respectively, to analyze the conductance changes with the rotation of naphthyl groups along 1,3-butadiynyl axis. , As depicted in Figure , with the conformational flipping through the rotation of naphthyl groups along 1,3-butadiynyl axis, molecule 1 shows the conductance fluctuation around 10 –2 to 10 –3 G 0 , while the conductance undulates around 10 –4 to 10 –5 G 0 for molecule 2 and around 10 –3 to 10 –4 G 0 for molecule 3 , where G 0 represents the conductance quantum …”

“…Molecular machine, including molecular rotor, gear, and crank, mimics the behavior of full-size machine and demonstrates the potential applications in the fields such as the ferroelectric and stimuli-responsive materials. − As a crucial prerequisite of utilization, accurately understanding the molecular internal motion is usually conducted by spectroscopic methods such as NMR and dielectric studies. , However, spectral characterizations in macroscopic aspect only describe the statistic result of molecular aggregation. In contrast, capturing the dynamic behavior for a single molecular machine, which provides the availability of obtaining more microscopic information at single-molecule level, is still a challenge due to the requirement of extreme resolution for accurately capturing and in situ observing the internal behavior of single molecule. , …”

Silicon – single molecule – silicon circuits

“…[64][65][66] To make robust devices of atomic dimensions, structural regularity and stability is important, and hence covalent bonding of molecules to silicon offers new technology directions; related covalent-bonding applications involving, e.g., graphene point contacts are also of modern interest. [67][68][69] To date, two types of silicon  molecule  silicon junctions have been prepared using scanning-tunnelling microscopy (STM) technology: "blinking" junctions, formed by holding a silicon STM tip fixed above a SAM of the molecule pre-prepared on a Si(111)-H substrate, and "break-junction" (STMBJ) junctions formed by crashing a silicon tip into a silicon substrate and then withdrawing the tip. Figure 1 illustrates the two approaches.…”

A Review of Sensors and Biosensors Modified with Conducting Polymers and Molecularly Imprinted Polymers Used in Electrochemical Detection of Amino Acids: Phenylalanine, Tyrosine, and Tryptophan

“…Electrochemical methods based on achieving sensors and biosensors [15,37,49,92] Medium Instrumental (electrical methods [122], optical methods [123], thermal methods [124], magnetic methods, and radiochemical methods [125] Low Chemical methods (volumetry, gravimetry, precipitation methods) [126] The disadvantages connected with electrochemical methods have stimulated researchers to improve the properties and performances of sensors and biosensors using, for the quantitative determination of AAs, Phe, Tyr, and Trypt, resorting to their modification, either with CPs doped with electroactive ions or with MIPs. Thus, researchers highlighted the unique properties of these devices: their optical, electrical, and mechanical properties, increased stability, high response rate, and increased sensitivity in the process of rapidly and precisely detecting AAs [127].…”