Gallium-based room-temperature liquid metals (LMs) combine the desirable properties of metals and liquids, and possess highly reactive surfaces, emerging as a promising component in constructing smart soft composites for various applications, particularly in biosensing and diagnostics. Herein, we report on the development of an ultrafast, real-time molecular diagnostic platform based on gallium-based LM nanoparticles (LM NPs) grafted with programmable DNA/polyacrylamide networks. LM NPs with strong and broadband plasmonic light absorption are demonstrated as efficient photothermal agents to enable stable temperature cycles, and the LM surface-initiated polymerization reaction allows direct grafting of DNA/polyacrylamide copolymer networks onto LM NPs, yielding core-shell nanocomposites with significantly enhanced photothermal stability and capable of participating in enzymatic amplification reactions. Thanks to the efficient cascading of the photothermal process and the PCR-based amplification process, real-time detection of nucleic acid targets within 6.5 min is achieved, and the testing of different viral and bacterial targets with high sensitivity and specificity is achieved. The broadband light absorption of LM NPs also allows the molecular diagnostic platform works under portable LED devices, such as a LED flashlight, which can be further developed into low-cost, rapid POCT molecular diagnostic devices for practical disease diagnosis and other applications.

The keto-enol tautomerism, involving a reversible isomerization of the molecule, plays a critical role in organic synthesis, biological activity, and molecular-scale charge transport. It is therefore essential to manipulate the process of keto-enol tautomerism. Unlike typical ketones, β-diketones exist dominantly in the enol form and it is a great challenge to realize enol-keto tautomerism due to the formation of intramolecular hydrogen bonds in the enol form. Here, via in situ monitoring of the conductance evolution of thousands of single-molecule junctions, we demonstrated that the enol → keto transformation can be significantly promoted by confined ultraviolet (UV) irradiation at an extremely low intensity (1‰ of sunshine) employing antenna electrodes. Our study reveals that the conductance of the enol form is an order of magnitude larger than that of the keto form although both have similar molecular lengths and identical anchoring groups, and the enol form shows a current rectification behaviour which is completely absent in the keto form. Supported by UV-vis measurements, wavelength-dependent conductance measurements, and theoretical calculations, the mechanism for the enol → keto transformation promoted by the gap-electrode-confined optical field was elucidated, offering a new strategy to regulate the tautomerism processes at the single molecule level, and implying a potential multi-functional application of β-diketones in the fabrication of rectifiers and synchronous switches.

Efficiently manipulating charge transport at the molecular level is critical to developing multifunctional and responsive molecular electronic devices. Here, we report the first electroresponsive tristate switch in a supramolecular circuit, overcoming the binary limitation and enabling richer logic encoding, governed solely by a bias voltage (electric field). At low electric fields, p ‐phenylenediamine (PPD) molecules exhibit a high‐conductance state, which transitions successively to two distinct low‐conductance states as the external electric field strength increases. This precise control of supramolecular junctions through electric field manipulation achieved an on/off ratio G H /G L of ∼1.25×10 3 , which is one of the largest values reported to date. Flicker noise analysis and density functional theory calculations reveal the intrinsic mechanism for the observation, i.e ., electric field promoting the formation of trimer supramolecular junctions leads to the striking on/off ratio. These findings provide new insights into the design of molecular circuits with tunable conductance, paving a way for the design of molecular computation, memory devices, and sensors.

A comprehensive understanding of carrier transport in photoisomeric molecular junctions is crucial for the rational design and delicate fabrication of single-molecule functional devices. It has been widely recognized that the conductance of azobenzene (a class of photoisomeric molecules) based molecular junctions is mainly determined by photoinduced conformational changes. In this study, it is demonstrated that the most probable conductance of amine-anchored azobenzene-based molecular junctions increases continuously upon UV irradiation. In contrast, the conductance of pyridyl-anchored molecular junctions with an identical azobenzene core exhibits a contrasting trend, highlighting the pivotal role that anchoring groups play, potentially overriding (even reversing) the effects of photoinduced conformational changes. It is further demonstrated that the molecule with cis-conformation cannot be fully mechanically stretched into the trans-conformation, clarifying that it is a great challenge to realize a reversible molecular switch by purely mechanical operation. Additionally, it is revealed that the coupling strength of pyridyl-anchored molecules is dramatically weakened when the UV irradiation time is prolonged, whereas it is not observed for amine-anchored molecules. The mechanisms for these observations are elucidated with the assistance of density functional theory calculations and UV-Vis spectra combined with flicker noise measurements which confirm the photoinduced conformational changes, providing insight into understanding the charge transport in photoisomeric molecular junctions and offering a routine for logical designing synchro opto-mechanical molecular switches.

AbstractThanks to their excellent bond strength, phenyl‐based molecules with thiol anchoring groups are extensively employed to form stable single‐molecule junctions. However, two critical questions are still not answered which seriously hinder high‐yield establishing reliable molecular functional devices: (1) Whether molecular dimer junctions will be formed, and if this is the case, whether the dimerization is caused by intermolecular disulfide bonds or π–π stacking of phenyl rings; (2) Upon a mechanical‐compression force, is it possible that both anchoring groups of the molecule bond to the same electrode instead of bridging two opposite electrodes, which would drastically reduce the yield of the molecular junctions. Here, combining UV‐Vis/Raman spectroscopy of bulk molecules and conductance/flicker‐noise measurements of single molecules, we give compelling evidence that molecular dimers naturally form under ambient conditions, primarily via disulfide bonds rather than by π–π stacking. We further proposed a technique, named electrode‐compression‐hold‐on (ECHO), and reveal that the two thiol groups of phenyl‐backboned molecules will bond to the same electrode upon a compression force with a prolongated ECHO time. In contrast, the compression‐time‐dependent phenomenon is not observed for alkyl‐backboned molecules. The underlying mechanism for these unprecedented observations is elucidated, shedding light on the yield of molecular junctions.

The current densities in nowadays electronic circuitry are close to the electromigration threshold that may result in the fracture of circuits due to electromigration, hampering further miniaturization of integrated chips. Flexible electronic devices, which use a flexible material instead of rigid silicon as a substrate, might be prone to fracture problems also due to obligatory mechanical deformation. However, finding the location of fractured nanogaps and in situ repairing such atomic‐scale fractured circuits are currently unavailable. To this end, a method is developed to in situ heal nanogaps as large as 20 nm between metallic electrodes on the polyimide (PI)‐covered substrate via voltage sweeping, which is typically employed to generate nanogaps rather than heal nanogaps. The reconnection of nanoelectrodes is realized only when the underneath PI is treated with oxygen plasma etching. Assisted by X‐ray photoelectron spectroscopy, it is revealed that inductively coupled O 2 plasma etching not only changes the surface topography but also changes the chemical binding structure of PI, which in return can be used to immobilize metal atoms migrating along the PI surface to gradually close the nanogap, providing an in situ self‐healing paradigm for repairing the atomic scale fractured circuits.

Via conductance measurements of thousands of single-molecule junctions, we report that the pi-pi coupling between neighboring aromatic molecules can be manipulated by laser illumination. We reveal that this optical manipulation originates from the optical plasmonic gradient force generated inside the nanogaps, in which the gapped antenna electrodes act as optical tweezers pushing the neighboring molecules closer together. These findings offer a nondestructive approach to regulate the interaction of the molecules, deepening the understanding of the mechanism of in teraction, and open an avenue to manipulate the relative position of extremely small objects down to the scale of single molecules.

The quantum interference (QI) effect plays a significant role in molecular electronics since offers an effective method to manipulate the charge transport through single-molecule junctions. However, tuning the QI effect in single-molecule junctions faces a formidable challenge due to the absence of technical approaches and limited theory. Here, we demonstrate, for the first time, that electrostatic gating can be a great candidate for the control of QI, thus manipulating the electron transport properties, due to the capability of the molecular orbitals shifting under the gating effect. Our calculations suggest that a switch between constructive and destructive QI effects can be realized as a result of the gating effect. The gated transition from constructive QI to destructive QI can lead to a dramatic conductance variation over one order of magnitude in anthracene-based molecular junctions. This control of the QI effect using electrostatic gating paves the way for the next generation of QI-based field-effect transistors.

The manipulation of single molecules has attracted extensive attention because of their promising applications in chemical, biological, medical, and materials sciences. Optical trapping of single molecules at room temperature, a critical approach to manipulating the single molecule, still faces great challenges due to the Brownian motions of molecules, weak optical gradient forces of laser, and limited characterization approaches. Here, we put forward localized surface plasmon (LSP)-assisted trapping of single molecules by utilizing scanning tunneling microscope break junction (STM-BJ) techniques, which could provide adjustable plasmonic nanogap and characterize the formation of molecular junction due to plasmonic trapping. We find that the plasmon-assisted trapping of single molecules in the nanogap, revealed by the conductance measurement, strongly depends on the molecular length and the experimental environments, i.e., plasmon could obviously promote the trapping of longer alkane-based molecules but is almost incapable of acting on shorter molecules in solutions. In contrast, the plasmon-assisted trapping of molecules can be ignored when the molecules are self-assembled (SAM) on a substrate independent of the molecular length.

The ability to precisely regulate the size of a nanogap is essential for establishing high-yield molecular junctions, and it is crucial for the control of optical signals in extreme optics. Although remarkable strategies for the fabrication of nanogaps are proposed, wafer-compatible nanogaps with freely adjustable gap sizes are not yet available. Herein, two approaches for constructing in situ adjustable metal gaps are proposed which allow Ångstrom modulation resolution by employing either a lateral expandable piezoelectric sheet or a stretchable membrane. These in situ adjustable nanogaps are further developed into in-plane molecular break junctions, in which the gaps can be repeatedly closed and opened thousands of times with self-assembled molecules. The conductance of the single 1,4-benzenediamine (BDA) and the BDA molecular dimer is successfully determined using the proposed strategy. The measured conductance agreeing well with the data by employing another well-established scanning tunneling microscopy break junction technique provides insight into the formation of molecule dimer via hydrogen bond at single molecule level. The wafer-compatible nanogaps and in-plane dynamical break-junctions provide a potential approach to fabricate highly compacted devices using a single molecule as a building block and supply a promising in-plane technique to address the dynamical properties of single molecules.

>Molecular chirality is a widespread phenomenon in nature,playing a critical role in various fields such as chemistry [1],life sciences [2], and materials science [3], and has therefore attracted significant attention and research by scholars [4–6].However, the chirality in chemical reactions is often dynamic, making real-time monitoring of chiral changes during chemical reactions at the single-molecule level extremely challenging.

The molecular binding orientation with respect to the electrode plays a pivotal role in determining the performance of molecular devices. However, accomplishing in situ modulation of single-molecule binding orientation remains a great challenge due to the lack of suitable testing systems and characterization approaches. To this end, by employing a developed STM-BJ technique, we demonstrate that the conductance of pyridine-anchored molecular junctions decreases as the applied voltage increases, which is determined by the repeated formation of thousands of gold-molecule-gold dynamic break junctions. In contrast, the static fixed molecular junctions (the distance between two electrodes is fixed) with identical molecules exhibit a reverse tendency as the bias voltage increases. Supported by flicker noise measurements and theoretical calculations, we provide compelling evidence that the orientation of nitrogen-gold bonds (a universal coordinate bond) in the pyridine-anchored molecular junctions can be manipulated to align with the electric field by the synergistic action of the mechanical stretching force and the electric fields, whereas either stimulus alone cannot achieve the same effect. Our study provides a framework for characterizing and regulating the orientation of a single coordinate bond, offering an approach to control electron transport through single molecular junctions.