Cascade-Gates Guarded Asymmetrical Nanochannel Membrane: An Interference-Free Device for Straightforward Detection of Trace Biomarker in Undiluted Serum

Accurate detection of trace biomarkers in biological samples is a key task in diagnostic testing, but it remains challenging due to the high concentration of other physiologically relevant interferences. This work presents a new electrochemiluminescence (ECL) sensing device based on a bio-inspired nanochannel membrane (NM) guarded with two differential gates. The recognition event at the aptamer gate is followed by the permitting of stimulator transport toward the metal-organic framework (MOF) gate. Proof of concept application is evaluated using cytochrome C (Cytc) as the analyte, and glucose, a commonly existing nutriment as the stimulator. The oxidase-mimic plasmonic nanoparticles induce an effective release of ECL luminophore from the MOF gate. This cascade-gates guarded NM can effectively separate biological matrices from the detection cell. Consequently, the proposed system can achieve direct sensing of 1.0 nm Cytc in undiluted serum within the threshold concentrations of leukemia and lymphoma, making it attractive for point-of-care applications.

Photoresponsive Solid Nanochannels Membranes: Design and Applications

Light stimuli have notable advantages over other environmental stimuli, such as more precise spatial and temporal regulation, and the ability to serve as an energy source to power the system. In nature, photoresponsive nanochannels are important components of organisms, with examples including the rhodopsin channels in optic nerve cells and photoresponsive protein channels in the photosynthesis system of plants. Inspired by biological channels, scientists have constructed various photoresponsive, smart solid-state nanochannels membranes for a range of applications. In this review, the methods and applications of photosensitive nanochannels membranes are summarized. The authors believe that this review will inspire researchers to further develop multifunctional artificial nanochannels for applications in the fields of biosensors, stimuli-responsive smart devices, and nanofluidic devices, among others.

A highly selective ATP-responsive biomimetic nanochannel based on smart copolymer

ATP-sensitive potassium (K_ATP) channels couple intracellular metabolism to the electrical activity by regulating K⁺ flux across the plasma membrane, thus playing an important role in both normal and pathophysiology. To understand the mechanism of ATP regulating biological ion channels, developing an ATP-responsive artificial nanochannel is an appealing but challenging topic because K_ATP channel is a heteromultimer of two subunits (potassium channel subunit (Kir6.x) and sulfonylurea receptor (SUR)) and exhibit dynamic functions with adjustability and reversibility. Inspired by the structure of K_ATP channels, we designed a smart copolymer modified nanochannel that may address the challenge. In the tricomponent poly(N-isopropylacrylamide) (PNIPAAm, PNI)-based copolymer system, phenylthiourea was used to bind the phosphate units of nucleotides and phenylboronic acid was introduced to combine the pentose ring of the nucleoside unit. Besides, a -COOH group with electron-withdrawing property was added into the phenylthiourea units, which may promote the hydrogen-bond-donating ability of thiourea. Specially, the smart copolymer not only provided static binding sites for recognition but also translated the recognition of ATP into their dynamic conformational transitions by changing the hydrogen-bonding environments surrounding PNIPAAm chains, thus achieving the gating function of nanochannel, which resembled the integration and coordination of Kir6.x and SUR units in active K_ATP. The ATP-regulated ion channel exhibited excellent stability and reversibility. This study is the first example showing how to learn from nature to assemble the ATP-responsive artificial nanochannel and demonstrate the possible mechanism of ATP gating.

Exploiting Free-Standing p-CuO/n-TiO2 Nanochannels as a Flexible Gas Sensor with High Sensitivity for H2S at Room Temperature

Hydrogen sulfide (H₂S) is an extremely hazardous gas and is harmful to human health and the environment. Here, we developed a flexible H₂S gas-sensing device operated at room temperature (25 °C) based on CuO nanoparticles coated with free-standing TiO₂-nanochannel membranes that were prepared by simple electrochemical anodization. Benefiting from the modulated conductivity of the CuO/TiO₂ p-n heterojunction and a unique nanochannel architecture, the traditional thermal energy was innovatively replaced with UV irradiation (λ = 365 nm) to provide the required energy for triggering the sensing reactions of H₂S. Importantly, upon exposure to H₂S, the p-n heterojunction is destroyed and the newly formed ohmic contact forms an antiblocking layer at the interface of CuS and TiO₂, thus making the sensing device active at room temperature. The resulting CuO/TiO₂ membrane exhibited a notable detection sensitivity for H₂S featuring a minimum detection limit of 3.0 ppm, a response value of 46.81% against 100 ppm H₂S gas, and a rapid response and recovery time. This sensing membrane also demonstrated excellent durability, long-term stability, and wide-range response to a concentration of up to 400 ppm in the presence of 40% humidity as well as outstanding flexibility and negligible change in electrical measurements under various mechanical stability tests. This study not only provides a new strategy to design a gas sensor but also paves a universal platform for sensitive gas sensing.

Fabrication of Homochiral Metal-Organic Frameworks in TiO2 Nanochannels for In Situ Identification of 3,4-Dihydroxyphenylalanine Enantiomers

Enantioselective identification of chiral molecules is important for biomedical and pharmaceutical research. However, owing to identical molecular formulas and chemical properties of enantiomers, signal transduction and amplification are still the two major challenges in chiral sensing. In this study, we developed an enantioselective membrane by integrating homochiral metal-organic frameworks (MOFs) with nanochannels for the sensitive identification and quantification of chiral compounds. The membrane was designed using a TiO₂ nanochannel membrane (TiNM) as the metal ion precursor of MOFs (using MIL-125(Ti)) and incorporating l-glutamine (l-Glu) into the framework of MIL-125(Ti). Using 3,4-dihydroxyphenylalanine (DOPA) as the model analyte, the as-prepared homochiral l-Glu/MIL-125(Ti)/TiNM exhibits a remarkable chiral recognition to d-DOPA than l-DOPA. More importantly, benefiting from the highly enlarged surface area and confinement effect provided by the MOFs-in-nanochannel architecture, the discrimination for chiral recognition is largely amplified through the chelation interaction of Fenton-like activity of Fe³⁺ onto DOPA. Using 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonate) (ABTS) as the substrate, the positively charged ABTS^•+ product via Fenton-like reaction induces significant ionic transport changes in nanochannels, which in turn provides information about chiral recognition. This innovative signal amplification strategy on homochiral nanochannels might pave a new way for sensitive monitoring and chiral recognition.

Smart pH-Modulated Two-Way Photoswitch Based on a Polymer-Modified Single Nanochannel

In this article, we have demonstrated a smart pH-modulated two-way photoswitch that can reversibly switch ion transport under alternating light exposure over a wide pH range. This photoswitch was prepared by functionalizing the interior of a single conical glass nanochannel with a poly-spiropyran-linked methacrylate (P-SPMA) polymer through surface-initiated atom transfer radical polymerization. The P-SPMA polymer brushes comprise functional groups that are responsive to light and pH, which can cause configuration and charge changes to affect the properties of the nanochannel wall. The SPMA polymer-modified nanochannel not only reversibly controlled ion transport under alternating light irradiation but also efficiently and flexibly regulated the direction and extent of the ion transport based on the pH. This two-way photoswitch exhibits the considerable potential of photoresponsive polymers for the advancement of "intelligent" bionic nanochannel devices for ion screening and optical sensing in various applications.

Titanium Dioxide Derived Materials with Superwettability

Titanium dioxide (TiO2) is widely used in various fields both in daily life and industry owing to its excellent photoelectric properties and its induced superwettability. Over the past several decades, various methods have been reported to improve the wettability of TiO2 and plenty of practical applications have been developed. The TiO2-derived materials with different morphologies display a variety of functions including photocatalysis, self-cleaning, oil-water separation, etc. Herein, various functions and applications of TiO2 with superwettability are summarized and described in different sections. First, a brief introduction about the discovery of photoelectrodes made of TiO2 is revealed. The ultra-fast spreading behaviors on TiO2 are shown in the part of ultra-fast spreading with superwettability. The part of controllable wettability introduces the controllable wettability of TiO2-derived materials and their related applications. Recent developments of interfacial photocatalysis and photoelectrochemical reactions with TiO2 are presented in the part of interfacial photocatalysis and photoelectrochemical reactions. The part of nanochannels for ion rectification describes ion transportation in nanochannels based on TiO2-derived materials. In the final section, a brief conclusion and a future outlook based on the superwettability of TiO2 are shown.

Rapid Capture and Photocatalytic Inactivation of Target Cells from Whole Blood by Rotating Janus Nanotubes

Effective isolation and removal of target tumor cells from patients' peripheral blood are of great importance to clinical prognosis and recovery. However, the extremely low quantity of target cells in peripheral blood becomes one of the challenges in this respect. Herein, we design and synthesize an innovative nanostructure based on magnetic TiO₂ nanotubes with Pt nanoparticles' asymmetrical decoration for effectively capturing and inactivating target cells. Using CCRF-CEM as the model cell, the resulting nanotubes with accurate modification of recognition probes exhibit high selectivity and cell-isolation efficiency upon real blood samples. Particularly, the target cells are selectively captured at a low concentration with a recovery rate of 73.0 ± 11.5% at five cells per milliliter for whole blood samples. Consequently, benefitting from the remarkable photocatalytic activity of the Janus nanotubes, these isolated cells can be rapidly inactivated via light-emitting diode (LED) irradiation with an ignorable effect on normal cells. This work offers a new paradigm for high-efficient isolating/killing target cells from a complex medium.

Insight of the Influence of Magnetic-Field Direction on Magneto-Plasmonic Interfaces for Tuning Photocatalytical Performance of Semiconductors

Boosting photocatalytic performance via external fields is an alternative and effective solution for improving the application performance of existing photocatalysts. Herein, using α-Fe₂O₃-decorated TiO₂ nanotube arrays as a model, we demonstrate the influence of magnetic field (MF)-direction on the photogenerated charge-carrier transfer behavior at plasmonic metal/semiconductor interfaces. For the first time, the photocatalytic activity is also found to correlate with the plasmonic metal species while applying an external MF. As verified by first-principles calculations, the spin-orbit coupling of metal contributes to the charge-carrier transfer. To highlight the anisotropic MF-tuning effect in practical applications, the as-prepared architecture is applied for photocatalysis-triggered drug delivery. The delivery rate can be remarkably accelerated by ∼38% under a tiny MF (0.4 T) with the proper direction. The findings in this research may provide new insight into designing semiconductor architectures for boosting the photocatalytical performance in an external MF.

NIR Light-Driven Photocatalysis on Amphiphilic TiO2 Nanotubes for Controllable Drug Release

Titanium dioxide (TiO₂) nanomaterials have attracted much interest in life science and biological fields because of their excellent photocatalytic activity and good biocompatibility. However, owing to its wide band gap, photocatalysis of TiO₂ can be only triggered by UV light. The limited transparent depth of UV light and the generated reactive oxygen species (ROSs) cause inflammation response of skin tissue, thus posing two major challenges in the photocatalytic application of TiO₂-based materials in drug delivery and other biotechnology fields. Here, we propose an upconversion-related strategy to enable the photocatalytic activity of TiO₂ nanotubes in near-infrared light and apply the system as a controllable drug delivery platform. More importantly, the ROS-induced cytotoxicity and the preleaching of payloads are significantly reduced on the as-proposed amphiphilic TiO₂ nanotubes. The hydrophobic monolayers are served as a "cap" to provide protection for ROS-induced inflammation and long-term storability. This amphiphilic drug delivery system broadens the potential applications of TiO₂-based nanomaterials in biomedicine.