Phosphoprotein Detection with a Single Nanofluidic Diode Decorated with Zinc Chelates

Regulation of Protein Transport in Functionalized PET Nanopores

Facilitated translocation is a critical mechanism for transporting substances in biological systems, where molecular and ionic species move across the biological membrane with the help of specific transmembrane protein ion channels. In this work, we systematically examined protein transport in three poly(ethylene terephthalate) (PET) nanopores modified with different types of surface functions (hydroxyl, phenyl, and amine). We found that the event signature as well as the kinetics and thermodynamics of protein movement in the PET nanopore varied significantly with the change in the surface function in the pore. In addition to the electrophoretic effect, other factors such as diffusion, electro-osmotic effect, ion selectivity of the channel, and affinity strength between the protein species and the surface functional group of the nanopore also play significant roles in the protein transport. Although properly functionalized individual PET nanopores can be used as stochastic elements for rapid protein differentiation and characterization, enhanced resolution and accuracy could be accomplished by employing an array of PET nanopores having different inner surface functional groups to characterize proteins based on their collective responses. Given the important roles proteins play in living organisms and their applications as biomarkers in early disease diagnosis and prognosis, the pattern-recognition solid-state nanopore-sensing strategy for protein detection and characterization developed in this work may find useful applications in various fields.

Pore-Size-Dependent Role of Functional Elements at the Outer Surface and Inner Wall in Single-Nanochannel Biosensors

Biological nanopores feature functional elements on the outer surfaces (FEOS) and inner walls (FEIW), enabling precise control over ions and molecules with exceptional sensitivity and specificity. This provides valuable inspiration to scientists for the development of intelligent artificial nanochannel-based platforms, with a wide range of potential applications, including biosensors. Much effort has been dedicated to investigating the distinct contribution of FEOS and FEIW of multichannel membrane biosensors. However, the intricate interactions among neighboring pores in multichannel biosensors have presented challenges. This underscores the untapped potential of single nanochannels as ideal candidates in this field. Here, we employed single nanochannel membranes with different pore sizes to investigate the distinct contributions of FEIW and FEOS to single-nanochannel biosensors, combined with numerical simulations. Our findings revealed that alterations in the negative charges of FEIW and FEOS, induced by target binding, have differential effects on ion transport, contingent upon the degree of nanoconfinement. In the case of smaller pores, such as 20 nm, the ion concentration polarization driven by FEIW can independently control ion transport through the surface's electric double layer. However, as the pore size increases to 40-60 nm, both FEIW and FEOS become essential for effective ion concentration polarization. When the pore size reaches 100 nm, both FEIW and FEOS are ineffective and thus unsuitable for biosensors. Simulations demonstrate that the observed phenomena can be attributed to the interactions between the charges of FEIW and FEOS within the overlapping electric double layer under confinement. These results underscore the critical role of pore size as a key parameter in governing the functionality of probes within or on nanopore-based biosensors as well as in the design of nanopore-based devices.

The Detection of Trace Metal Contaminants in Organic Products Using Ion Current Rectifying Quartz Nanopipettes

While ion current rectification (ICR) in aprotic solvent has been fundamentally studied, its application in sensing devices lacks exploration. The development of sensors operable in these solvents is highly beneficial to the chemical industry, where polar aprotic solvents, such as acetonitrile, are widely used. Currently, this industry relies on the use of inductively coupled plasma mass spectrometry (ICP-MS) and optical emission spectroscopy (OES) for the detection of metal contamination in organic products. Herein, we present the detection of trace amounts of Pd2+ and Co2+ using ion current rectification, in cyclam-functionalized quartz nanopipettes, with tetraethylammonium tetrafluoroborate (TEATFB) in MeCN as supporting electrolyte. This methodology is employed to determine the concentration of Pd in organic products, before and after purification by Celite filtration and column chromatography, obtaining comparable results to ICP-MS within minutes and without complex sample preparation. Finite element simulations are used to support our experimental findings, which reveal that the formation of double-junction diodes in the nanopore enables trace detection of these metals, with a significant response from baseline even at picomolar concentrations.

Solid-State Nanopore/Nanochannel Sensors with Enhanced Selectivity through Pore-in Modification

Nanopore sensing technology, as an emerging analytical method, has the advantages of simple operation, fast output, and label-free and has been widely used in fields such as protein analysis, gene sequencing, and biomarker detection. Inspired by biological ion channels, scientists have prepared various artificial solid-state nanopores/nanochannels. Biological ion channels have extremely high ion transport selectivity, while solid-state nanopores/nanochannels have poor selectivity. The selectivity of solid-state nanopores and nanochannels can be enhanced by modifying channel charge, varying pore size, incorporating specific chemical functionality, and adjusting operating (or solution) conditions. This Perspective highlights pore-in modification strategies for enhancing the selectivity of solid-state nanopore/nanochannel sensors by summarizing the articles published in the last 10 years. The future development prospects and challenges of pore-in modification in solid-state nanopore and nanochannel sensors are discussed. This Perspective helps readers better understand nanopore sensing technology, especially the importance of detection selectivity. We believe that solid-state nanopore/nanochannel sensors will soon enter our homes after various challenges.

In Situ Growth Intercalation Structure MXene@Anatase/Rutile TiO2 Ternary Heterojunction with Excellent Phosphoprotein Detection in Sweat

Abnormal protein phosphorylation may relate to diseases such as Alzheimer's, schizophrenia, and Parkinson's. Therefore, the real-time detection of phosphoproteins in sweat was of great significance for the early knowledge, detection, and treatment of neurological diseases. In this work, anatase/rutile TiO₂ was in situ grown on the MXene surface to constructing the intercalation structure MXene@anatase/rutile TiO₂ ternary heterostructure as a sensing platform for detecting phosphoprotein in sweat. Here, the intercalation structure of MXene acted as electron and diffusion channels for phosphoproteins. The in situ grown anatase/rutile TiO₂ with n-n-type heterostructure provided specific adsorption sites for the phosphoproteins. The determination of phosphoprotein covered concentrations in sweat, with linear range from 0.01 to 1 mg/mL, along with a low LOD of 1.52 μM. It is worth noting that, since the macromolecular phosphoprotein was adsorbed on the surface of the material, the electrochemical signal gradually decreased with the increase of phosphoprotein concentration. In addition, the active sites in the MXene@anatase/rutile TiO₂ ternary heterojunction and synergistic effect of the heterojunction were verified by first-principle calculations to further realize the response to phosphoproteins. Additionally, the effective diffusion capacity and mobility of phosphoprotein molecules in the ternary heterojunction structure were studied by molecular dynamics simulation. Furthermore, the constructed sensing platform showed high selectivity, repeatability, reproducibility, and stability, and this newly developed sensor can detect for phosphoprotein in actual sweat samples. This satisfactory sensing strategy could be promoted to realize the noninvasive and continuous detection of sweat.

Bio-inspired Track-Etched Polymeric Nanochannels: Steady-State Biosensors for Detection of Analytes

Bio-inspired polymeric nanochannel (also referred as nanopore)-based biosensors have attracted considerable attention on account of their controllable channel size and shape, multi-functional surface chemistry, unique ionic transport properties, and good robustness for applications. There are already very informative reviews on the latest developments in solid-state artificial nanochannel-based biosensors, however, which concentrated on the resistive-pulse sensing-based sensors for practical applications. The steady-state sensing-based nanochannel biosensors, in principle, have significant advantages over their counterparts in term of high sensitivity, fast response, target analytes with no size limit, and extensive suitable range. Furthermore, among the diverse materials, nanochannels based on polymeric materials perform outstandingly, due to flexible fabrication and wide application. This compressive Review summarizes the recent advances in bio-inspired polymeric nanochannels as sensing platforms for detection of important analytes in living organisms, to meet the high demand for high-performance biosensors for analysis of target analytes, and the potential for development of smart sensing devices. In the future, research efforts can be focused on transport mechanisms in the field of steady-state or resistive-pulse nanochannel-based sensors and on developing precisely size-controlled, robust, miniature and reusable, multi-functional, and high-throughput biosensors for practical applications. Future efforts should aim at a deeper understanding of the principles at the molecular level and incorporating these diverse pore architectures into homogeneous and defect-free multi-channel membrane systems. With the rapid advancement of nanoscience and biotechnology, we believe that many more achievements in nanochannel-based biosensors could be achieved in the near future, serving people in a better way.

Zinc(ii) and copper(ii) complexes as tools to monitor/inhibit protein phosphorylation events

A perspective on the advance of copper(ii) and zinc(ii) complexes of varied ligand architectures as binders of phosphorylated peptides/proteins and as sensors of phosphorylation reactions is presented.