Photo-Enhanced Chemo-Transistor Platform for Ultrasensitive Assay of Small Molecules

Recent Advances in Xenes Based FET for Biosensing Applications

In recent years, monoelemental 2D materials (Xenes) such as graphene, graphdiyne, silicene, phosphorene, and tellurene, have gained significant traction in biosensing applications. Owing to their ultra-thin layered structure, exceptionally high specific surface area, unique surface electronic properties, excellent mechanical strength, flexibility, and other distinctive features, Xenes are recognized for their potential as materials with low detection limits, high speed, and exceptional flexibility in biosensing applications. In this review, the unique properties of Xenes, their synthesis, and recent theoretical and experimental advances in applications related to biosensing, including DNA/RNA biosensors, protein biosensors, small molecule biosensors, cell, and ion biosensors are comprehensively summarized. Finally, the challenges and prospects of this emerging field are discussed.

Au confined covalent organic frameworks nanoenzyme integrated with sodium alginate microsphere for portable colorimetric tannic acid detection

Developing a portable, affordable, and instrument-free colorimetric sensor for tannic acid detection is crucial for food quality assessment and health monitoring. In this work, we designed a rapid and efficient colorimetric platform by integrating Au-modified covalent organic framework (COF) with sodium alginate hydrogel microspheres for tannic acid detection assisted by mobile phone photo technology. The Au NPs with an average size of 4 nm were reduced by the bipyridine nitrogen on the COF layer under light irradiation, which enhanced the peroxidase-like activity of the nanozyme. Furthermore, the adsorption, hydrogen-bond, and covalent interaction between tannic acid and sodium alginate make the functional hydrogel microspheres exhibit enhanced colorimetric performance, with a linear range from 5.0 to 130 μM and a detection limit of 0.091 μM. In addition, the obtained colorimetric sensor was effectively used for tannic acid analysis in grape beverages and model wine samples with good recovery. This work broadens the horizon for the synthesis and design of visual sensors with functional porous COFs-based nanozyme and the development of portable and low-cost sensors by combining hydrogel microspheres, which could be applied for food analysis and quality control in real environments.

Chiral Cross-Linked Covalent Organic Framework Films for Highly Sensitive Circularly Polarized Luminescence Probing

The development of covalent organic framework (COF) films featuring circular polarization luminescence (CPL) probing remains a formidable challenge. Herein, we developed a chiral cross-linked COF film to obtain uniform and dense chiral COF films (chirCOFilm) possessing highly sensitive CPL probing for enantiomers. The axial chiral cross-linkers (R-/S-BBNA) are initially introduced into the channels of a COF film (COFilm/R-BBNA or COFilm/S-BBNA) by the vapor-assisted epitaxial method. Then, olefin groups in R-/S-BBNA and COF layers undergo a chiral cross-linking reaction under UV irradiation, forming a chirCOFilm. The obtained chirCOFilms have strong chirality with mirror images, fluorescence discoloration, and intense CPL properties. A multitude of rich chiral photopatterns and chirCOFilm/PDMS flexible films are prepared taking advantage of the photochromic properties of the chirCOFilms during UV illumination, showing the potential application of advanced anticounterfeiting. More importantly, the chirCOFilms realize highly sensitive CPL probing of phenethylamine enantiomers at 5% concentration, which can hardly be achieved from their corresponding fluorescence probing. This study not only provides a new strategy for preparing chiral COF films using chiral cross-linking reaction but also opens a new avenue for achieving highly sensitive probing of enantiomers though CPL.

Construction of Guanidinium-Functionalized Covalent Organic Frameworks via Phototriggered Click Reaction as a Dual-Mode Accurate Sensor for Malondialdehyde

Malondialdehyde (MDA) serves as a pivotal indicator to estimate the lipid peroxidation status and as a biomarker for the assessment of oxidative stress and screening of disease by people excretion. However, most of the existing analytical methods for MDA suffer from complicated derivation, leading to poor accuracy and inconvenience. In this work, the guanidinium-functionalized covalent organic framework (COF) was delicacy-designed and used to tune the modular structure by the building blocks with condensation, phototriggered click reaction, and further guanidylation process. A methoxy-group-containing linker in the skeleton was adopted to form lone-pair delocalized oxygen atoms, trigger the resonance effect, attenuate the polarization of the C═N bond linkages, and weaken the interlayer repulsion, supporting the stability of the guest gating COF. The available guanidino groups grew from the ordered pore walls of the COF and served as the customized talon with an enhanced interaction site density to rapidly grab the target guest by charge-assisted strong hydrogen bonds and electrostatic attraction forces. This distinctive feature significantly bolstered sensitive signal transduction, enabling rapid MDA sensing (within 120 s) without derivation treatment, and achieved a calculated limit of detection (LOD) as low as 0.08 μM. With the accessible image-data transmission process, the portable dual-channel sensing platform achieved sensitive and accurate MDA monitoring.

Cation Enrichment Effect Modulated Nafion/Graphene Field-Effect Transistor for Ultrasensitive RNA Detection

The graphene field-effect transistor (GFET) biosensor serves as a foundational platform for detecting biomolecules, offering high conductivity, label-free operation, and easy integration. These features have garnered significant attention in biomarker detection. However, the presence of free cations in solution often leads to electrostatic shielding of negatively charged biomolecules, reducing GFET detection sensitivity (LOD ≥ 1 fM). Additionally, the limited capacitance change in GFET restricts its use as a response signal. This study introduces a cation enrichment electric field modulation strategy (CEEFMS) to enhance capacitance and Dirac voltage response during detection. The cation-enriched rough Nafion/graphene FET (CENG-FET) achieves RNA detection at the aM level. Utilizing total capacitance change and Dirac voltage shift as response signals, the CENG-FET demonstrates a wide linear range from 1 aM to 1 pM. These findings advance dual-signal detection strategies, reducing accidental inaccuracies in biomolecular sensing and paving the way for further research.

Photoelectrochemical Solution Gated Graphene Field-Effect Transistor Functionalized by Enzymatic Cascade Reaction for Organophosphate Detection

Solution Gated Graphene Field-Effect Transistors (SGGT) are eagerly anticipated as an amplification platform for fabricating advanced ultra-sensitive sensors, allowing significant modulation of the drain current with minimal gate voltage. However, few studies have focused on light-matter interplay gating control for SGGT. Herein, this challenge is addressed by creating an innovative photoelectrochemical solution-gated graphene field-effect transistor (PEC-SGGT) functionalized with enzyme cascade reactions (ECR) for Organophosphorus (OPs) detection. The ECR system, consisting of acetylcholinesterase (AChE) and CuBTC nanomimetic enzymes, selectively recognizes OPs and forms o-phenylenediamine (oPD) oligomers sediment on the PEC electrode, with layer thickness related to the OPs concentration, demonstrating time-integrated amplification. Under light stimulation, the additional photovoltage generated on the PEC gate electrode is influenced by the oPD oligomers sediment layer, creating a differentiated voltage distribution along the gate path. PEC-SGGT, inherently equipped with built-in amplification circuits, sensitively captures gate voltage changes and delivers output with an impressive thousandfold current gain. The seamless integration of these three amplification modes in this advanced sensor allows a good linear range and highly sensitive detection of OPs, with a detection limit as low as 0.05 pm. This work provides a proof-of-concept for the feasibility of light-assisted functionalized gate-controlled PEC-SGGT for small molecule detection.

2D Conjugated Polymer Thin Films for Organic Electronics: Opportunities and Challenges

2D conjugated polymers (2DCPs) possess extended in-plane π-conjugated lattice and out-of-plane π-π stacking, which results in enhanced electronic performance and potentially unique band structures. These properties, along with predesignability, well-defined channels, easy postmodification, and order structure attract extensive attention from material science to organic electronics. In this review, the recent advance in the interfacial synthesis and conductivity tuning strategies of 2DCP thin films, as well as their application in organic electronics is summarized. Furthermore, it is shown that, by combining topology structure design and targeted conductivity adjustment, researchers have fabricated 2DCP thin films with predesigned active groups, highly ordered structures, and enhanced conductivity. These films exhibit great potential for various thin-film organic electronics, such as organic transistors, memristors, electrochromism, chemiresistors, and photodetectors. Finally, the future research directions and perspectives of 2DCPs are discussed in terms of the interfacial synthetic design and structure engineering for the fabrication of fully conjugated 2DCP thin films, as well as the functional manipulation of conductivity to advance their applications in future organic electronics.

Chemical Sensors Based on Covalent Organic Frameworks

Covalent organic frameworks (COFs) are a type of crystalline porous polymer composed of light elements through strong covalent bonds. COFs have attracted considerable attention due to their unique designable structures and excellent material properties. Currently, COFs have shown outstanding potential in various fields, including gas storage, pollutant removal, catalysis, adsorption, optoelectronics, and their research in the sensing field is also increasingly flourishing. In this review, we focus on COF-based sensors. Firstly, we elucidate the fundamental principles of COF-based sensors. Then, we present the primary application areas of COF-based sensors and their recent advancements, encompassing gas, ions, organic compounds, and biomolecules sensing. Finally, we discuss the future trends and challenges faced by COF-based sensors, outlining their promising prospects in the field of sensing.