Setschenow Constant Prediction Based on the IEF-PCM Calculations

The Setschenow constant <i>K</i>_salt of a compound in NaCl solution is an important parameter. The solvent environment influences the geometries, energies, charge distributions, and other properties of solutes. The integral equation formalism polarizable continuum model (IEF-PCM) for solvent effects was used to optimize molecular geometries with the density functional theory method combined with Becke’s three-parameter hybrid functional and Lee–Yang–Parr’s gradient-corrected correlation functional at 6-31G­(d) level. Single-point energy calculations and natural bond orbital analyses were carried out with the same method. After 1672 molecular descriptors generation, four descriptors were selected to develop models for <i>K</i>_salt of 101 organic compounds, by using the genetic algorithm method together with multiple linear regression (MLR) technique. The optimal MLR and support vector machine models of <i>K</i>_salt have the mean root-mean-square errors of 0.0287 and 0.0227, respectively. Compared with previous models, the two models in this work have better predictive performance. Results of the study suggest that calculating molecular descriptors from IEF-PCM to predict the Setschenow constants <i>K</i>_salt of organic compounds in NaCl solution is feasible

Novel Aptasensor Platform Based on Ratiometric Surface-Enhanced Raman Spectroscopy

A novel aptasensor platform has been developed for quantitative detection of adenosine triphosphate (ATP) based on a ratiometric surface-enhanced Raman scattering (SERS) strategy. The thiolated 3′-Rox-labeled complementary DNA (cDNA) is first immobilized on the gold nanoparticle (AuNP) surface and then hybridizes with the 3′-Cy5-labeled ATP-binding aptamer probe (Cy5-aptamer) to form a rigid double-stranded DNA (dsDNA), in which the Cy5 and Rox Raman labels are used to produce the ratiometric Raman signals. In the presence of ATP, the Cy5-aptamer is triggered the switching of aptamer to form the aptamer–ATP complex, leading to the dissociation of dsDNA, and the cDNA is then formed a hairpin structure. As a result, the Rox labels are close to the AuNP surface while the Cy5 labels are away from. Therefore, the intensity of SERS signal from Rox labels increases while that from Cy5 labels decreases. The results show that the ratio between the Raman intensities of Rox labels and Cy5 labels is well linear with the ATP concentrations in the range from 0.1 to 100 nM, and the limit of detection reaches 20 pM, which is much lower than that of other methods for ATP detection and is also lower than that of SERS aptasensor for ATP detection. The proposed strategy provides a new reliable platform for the construction of SERS biosensing methods and has great potential to be a general method for other aptamer systems

Inhibition of dsDNA-Templated Copper Nanoparticles by Pyrophosphate as a Label-Free Fluorescent Strategy for Alkaline Phosphatase Assay

On the basis of the inhibition of double strand DNA (dsDNA)-templated fluorescent copper nanoparticles (CuNPs) by pyrophosphate (PPi), a novel label-free turn-on fluorescent strategy to detect alkaline phosphatase (ALP) under physiological conditions has been developed. This method relies on the strong interaction between PPi and Cu²⁺, which would hamper the effective formation of fluorescent CuNPs, leading to low fluorescence intensity. The ALP-catalyzed PPi hydrolysis would disable the complexation between Cu²⁺ and PPi, facilitating the formation of fluorescent CuNPs through the reduction by ascorbate in the presence of dsDNA templates. Thus, the fluorescence intensity was recovered, and the fluorescence enhancement was related to the concentration of ALP. This method is cost-effective and convenient without any labels or complicated operations. The present strategy exhibits a high sensitivity and the turn-on mode provides a high selectivity for the ALP assay. Additionally, the inhibition effect of phosphate on the ALP activity was also studied. The proposed method using a PPi substrate may hold a potential application in diagnosis of ALP-related diseases or evaluation of ALP functions in biological systems

Label-Free Photonic Crystal-Based β‑Lactamase Biosensor for β‑Lactam Antibiotic and β‑Lactamase Inhibitor

A simple, label-free, and visual photonic crystal-based β-lactamase biosensor was developed for β-lactam antibiotic and β-lactamase inhibitor in which the penicillinase (a β-lactamase) was immobilized on the pH-sensitive colloidal crystal hydrogel (CCH) film to form penicillinase colloidal crystal hydrogel (PCCH) biosensing film. The hydrolysis of penicillin G (a β-lactam antibiotic) can be catalyzed by penicillinase to produce penicilloic acid, leading to a pH decrease in the microenvironment of PCCH film, which causes the shrink of pH-sensitive CCH film and triggers a blue-shift of the diffraction wavelength. Upon the addition of β-lactamase inhibitor, the hydrolysis reaction is suppressed and no clear blue-shift is observed. The concentrations of β-lactam antibiotic and β-lactamase inhibitor can be sensitively evaluated by measuring the diffraction shifts. The minimum detectable concentrations for penicillin G and clavulanate potassium (a β-lactamase inhibitor) can reach 1 and 0.1 μM, respectively. Furthermore, the proposed method is highly reversible and selective, and it allows determination of penicillin G in fish pond water samples

Acetylcholinesterase Liquid Crystal Biosensor Based on Modulated Growth of Gold Nanoparticles for Amplified Detection of Acetylcholine and Inhibitor

A novel acetylcholinesterase (AChE) liquid crystal (LC) biosensor based on enzymatic growth of gold nanoparticles (Au NPs) has been developed for amplified detection of acetylcholine (ACh) and AChE inhibitor. In this method, AChE mediates the hydrolysis of acetylthiocholine (ATCl) to form thiocholine, and the latter further reduces AuCl₄^– to Au NPs without Au nanoseeds. This process, termed biometallization, leads to a great enhancement in the optical signal of the LC biosensor due to the large size of Au NPs, which can greatly disrupt the orientational arrangement of LCs. On the other hand, the hydrolysis of ATCl is inhibited in the presence of ACh or organophosphate pesticides (OPs, a AChE inhibitor), which will decrease the catalytic growth of Au NPs and, as a result, reduce the orientational response of LCs. On the basis of such an inhibition mechanism, the AChE LC biosensor can be used as an effective way to realize the detection of ACh and AChE inhibitors. The results showed that the AChE LC biosensor was highly sensitive to ACh with a detection limit of 15 μmol/L and OPs with a detection limit of 0.3 nmol/L. This study provides a simple and sensitive AChE LC biosensing approach and offers effective signal enhanced strategies for the development of enzyme LC biosensors

A Targeted, Self-Delivered, and Photocontrolled Molecular Beacon for mRNA Detection in Living Cells

The spatiotemporal dynamics of specific mRNA molecules are difficult to image and detect inside living cells, and this has been a significant challenge for the chemical and biomedical communities. To solve this problem, we have developed a targeted, self-delivered, and photocontrolled aptamer-based molecular beacon (MB) for intracellular mRNA analysis. An internalizing aptamer connected via a double-stranded DNA structure was used as a carrier probe (CP) for cell-specific delivery of the MB designed to signal target mRNA. A light activation strategy was employed by inserting two photolabile groups in the CP sequence, enabling control over the MB’s intracellular function. After the probe was guided to the target cell via specific binding of aptamer AS1411 to nucleolin on the cell membrane, light illumination released the MB for mRNA monitoring. Consequently, the MB is able to perform live-cell mRNA imaging with precise spatiotemporal control, while the CP acts as both a tracer for intracellular distribution of the MB before photoinitiation and an internal reference for mRNA ratiometric detection

Modulated Dye Retention for the Signal-On Fluorometric Determination of Acetylcholinesterase Inhibitor

A novel fluorometric assay method based on target-induced signal on was developed for acetylcholinesterase (AChE) inhibitor with obviously improved detection sensitivity. In this method, the AChE molecules catalyzed the hydrolysis of acetylthiocholine (ATCl) to form thiocholine, which in turn can specifically react with fluorescent squaraine derivative, a specific chemodosimeter for thiol-containing compounds, resulting in fluorescence quenching and offering a low fluorometric background for the further detection of AChE inhibitor. In the presence of AChE inhibitor, the catalytic hydrolysis of ATCl is blocked, and then the squaraine derivative remains intact and shows signal-on fluorescence. The amount of the remaining fluorescent squaraine derivative is positively correlated with that of the AChE inhibitor in solution. This new designed sensing system shows an obviously improved sensitivity toward target with a detection limit of 5 pg mL^–1 (0.018 nM) for the AChE inhibitor, comparing favorably with previously reported fluorometric methods. To our best knowledge, this new method is the first example of fluorometric enzymatic assay for AChE inhibitors based on such a signal-on principle and using a specific reaction, which has potential to offer an effective strategy for the detection of AChE inhibitors

Cell Membrane-Anchored Biosensors for Real-Time Monitoring of the Cellular Microenvironment

Cell membrane-anchored biochemical sensors that allow real-time monitoring of the interactions of cells with their microenvironment would be powerful tools for studying the mechanisms underlying various biological processes, such as cell metabolism and signaling. Despite the significance of these techniques, unfortunately, their development has lagged far behind due to the lack of a desirable membrane engineering method. Here, we propose a simple, efficient, biocompatible, and universal strategy for one-step self-construction of cell-surface sensors using diacyllipid-DNA conjugates as the building and sensing elements. The sensors exploit the high membrane-insertion capacity of a diacyllipid tail and good sensing performance of the DNA probes. Based on this strategy, we have engineered specific DNAzymes on the cell membrane for metal ion assay in the extracellular microspace. The immobilized DNAzyme showed excellent performance for reporting and semiquantifying both exogenous and cell-extruded target metal ions in real time. This membrane-anchored sensor could also be used for multiple target detection by having different DNA probes inserted, providing potentially useful tools for versatile applications in cell biology, biomedical research, drug discovery, and tissue engineering

Synthesis of WS_2<i>x</i>Se_{2–2<i>x</i>} Alloy Nanosheets with Composition-Tunable Electronic Properties

Two-dimensional (2D) layered transition metal dichalcogenides (TMDs) have recently emerged as a new class of atomically thin semiconductors for diverse electronic, optoelectronic, and valleytronic applications. To explore the full potential of these 2D semiconductors requires a precise control of their band gap and electronic properties, which represents a significant challenge in 2D material systems. Here we demonstrate a systematic control of the electronic properties of 2D-TMDs by creating mixed alloys of the intrinsically p-type WSe₂ and intrinsically n-type WS₂ with variable alloy compositions. We show that a series of WS_2<i>x</i>Se_{2–2<i>x</i>} alloy nanosheets can be synthesized with fully tunable chemical compositions and optical properties. Electrical transport studies using back-gated field effect transistors demonstrate that charge carrier types and threshold voltages of the alloy nanosheet transistors can be systematically tuned by adjusting the alloy composition. A highly p-type behavior is observed in selenium-rich alloy, which gradually shifts to lightly p-type, and then switches to lightly n-type characteristics with the increasing sulfur atomic ratio, and eventually evolves into highly n-doped semiconductors in sulfur-rich alloys. The synthesis of WS_2<i>x</i>Se_{2–2<i>x</i>} nanosheets with tunable optical and electronic properties represents a critical step toward rational design of 2D electronics with tailored spectral responses and device characteristics