Colorimetric aptasensor based on self-screened aptamers and cascaded catalytic reaction for the detection of quarantine plant bacteria.

Quarantine plant bacteria (QPB) are significant component of invasive alien species that result in substantial economic losses and serious environmental damage. Herein, a colorimetric aptasensor has been proposed based on the sandwich structure and the cascaded catalytic strategy for on-site detecting Xanthomonas hyacinthi, a type of QPB, in natural environments. The self-screened aptamer obtained through SELEX can bind to specific sites on the surface of viable organism with high affinity and specificity, which guarantees the selectivity of aptasensor. As an important part of the aptasensor, MIL-88-NH2(Fe) not only acts as a multifunctional carrier for both aptamers and glucose oxidase, but also catalyzes enzyme-like reaction because of specific surface area, amino and peroxidase-like activity. The present of Xanthomonas hyacinthi can trigger the formation of a sandwich structure and the occurrence of cascade catalytic reaction, enabling the detection with UV-Vis spectra and naked eyes. The proposed aptasensor presents a low detection limit of 2 cfu/mL and a wide linear range of 10 -107 cfu/mL. Compared to traditional detection methods for QPB, the reasonable design, high selectivity and convenience significantly improve the detection efficiency and contribute to environmental protection.

Electrochemical aptasensors based on porous carbon derived from graphene oxide/ZIF-8 composites for the detection of Erwinia cypripedii.

In this research, self-screening aptamer and MOFs-derived nanomaterial have been combined to construct electrochemical aptasensor for environmental detection. By utilizing the large specific surface area of reduced graphene oxide (rGO), ZIF-8 was grown in situ on surface of rGO, and the composites was pyrolyzed to obtain MOFs-derived porous carbon materials (rGO-NCZIF). Thanks to the synergistic effect between rGO and NCZIF, the complex exhibits remarkable characteristics, including a high electron transfer rate and electrocatalytic activity. In addition, the orderly arrangement of imidazole ligands within ZIF-8 facilitated the uniform doping of nitrogen elements into the porous carbon, thereby significantly enhancing its electrochemical performance. After carboxylation, rGO-NCZIF was functionalized with self-screening aptamer for fabricating electrochemical aptasensor, which can be used to detect Erwinia cypripedii, a kind of quarantine plant bacteria, with detection limit of 4.92 × 103 cfu/mL. Due to the simplicity and speed, the aptasensor is suitable for rapid customs inspection and quarantine. Additionally, the universality of this sensing strategy was verified through exosomes detection by changing the aptamer. The results indicated that the rGO-NCZIF-based electrochemical aptasensor had practical value in the environmental and medical fields.

Aggregation Inducing Reversible Conformational Isomerization of Surface Staple in Au18SR14 Nanoclusters.

The conformation of molecules and materials is crucial in determining their properties and applications. Here, this work explores the reversible transformation between two distinct conformational isomers in metal nanoclusters. This work demonstrates the successful manipulation of a controllable and reversible isomerization of Au18SR14 within an aqueous solution through two distinct methods: ethanol addition and pH adjustment. The initial driver is the alteration of the solution environment, leading to the aggregation of Au18SR14 protected by ligands with smaller steric hindrance. At the atomic level, the folding mode of the unique Au4SR5 staple underpins the observed structural transformation. The reversal of staple conformation leads to color shifting between green and orange-red, and tailors a second emission peak at 725 nm originating from charge transfer from the thiolate to the Au9 core. This work not only deepens the understanding of the surface structure and dual-emission of metal nanoparticles, but also enhances the comprehension of their isomerization.

Construction of self-enhanced luminescence probes based on Ti3C2 reducibility for ultrasensitive PNK analysis.

Au nano-clusters (Au NCs) were promising electrochemiluminescence (ECL) nano-materials. However, the small size of Au NCs presented a challenge in terms of their immobilization during the construction of an ECL biosensing platform. This limitation significantly hindered the wider application of Au NCs in the ECL field. In this work, we successfully used the reducibility of Ti3C2 to fabricate in situ a self-enhanced nano-probe Ti3C2-TiO2-Au NCs. The strategy of in situ generation not only improved the immobilization of Au NCs on the probe but also eliminated the requirement of adding reducing agents during preparation. In addition, in situ generated TiO2 could serve as a co-reaction accelerator, shortening the electron transfer distance between S2O82- and Au NCs, thereby improving the utilization of intermediates and enhancing the ECL response of Au NCs. The constructed ECL sensing platform could achieve sensitive detection of polynucleotide kinase (PNK). At the same time, the 5'-end phosphate group of DNA phosphorylation could chelate with a large amount of Ti on the surface of Ti3C2, thereby achieving the goal of specific detection of PNK. The sensor based on self-enhanced ECL probes had a broad dynamic range spanning for PNK detection from 10.0 to 1.0 × 107 µU mL-1, with a limit of detection of 1.6 µU mL-1. Moreover, the ECL sensor showed satisfactory detection performance in HeLa cell lysate and serum. This study not only provided insights for addressing the issue of ECL luminescence efficiency in Au NCs but also presented novel concepts for ECL self-enhancement strategies.

A novel self-enhanced ECL-RET aptasensor based on the bimetallic MOFs with homogeneous catalytic sites for kanamycin detection.

The inappropriate use of antibiotics undoubtedly poses a potential threat to public health, creating an increasing need to develop highly sensitive tests. In this study, we designed a new type of porphyrin metal-organic frameworks (Fe TCPP(Zn) MOFs) with homogeneous catalytic sites. The ferric-based metal ligands of Fe TCPP(Zn) MOFs acted as co-reaction accelerators, which effectively improved the conversion efficiency of H2O2 on the surface of MOFs, then increased the concentration of •OH surrounding porphyrin molecules to achieve self-enhanced electrochemiluminescence (ECL). Based on this, an aptasensor for the specific detection of kanamycin (KAN) in food and environmental water samples was constructed in combination with resonance energy transform (RET), in which Fe TCPP(Zn) MOFs were used as luminescence donor and AuNPs were used as acceptor. Under the best conditions, there was a good linear relationship between the ECL intensity and the logarithm of KAN concentration with a detection limit of 0.28 fM in the range of 1.0 × 10-7-1.0 × 10-13 M, demonstrating satisfactory selectivity and stability. At the same time, the complexity of the detection environment was reduced, which further realized the reliable analysis of KAN in milk, honey and pond water. Overall, this innovative self-enhanced ECL strategy provides a novel approach for constructing efficient ECL systems in MOFs, and also extends the application of MOFs to the analysis and detection of trace antibiotics in food and the environment.

Self-assembly of a AuNPs/Ti3C2 MXene hydrogel for cascade amplification of microRNA-122 biosensing.

A three-dimensional (3D) self-assembled AuNPs/Ti3C2 MXene hydrogel (AuNPs/Ti3C2 MXH) nanocomposite was prepared for the fabrication of a novel microRNA-122 electrochemical biosensor. The 3D hydrogel structure was gelated from two-dimensional MXene nanosheets with the assistance of graphite oxide and ethylenediamine. MXene hydrogels supported the in situ formation of Au nanoparticles (AuNPs) that predominantly exploring the (111) facet, and these AuNPs are utilized as carriers for hairpin DNA (hpDNA) probes, facilitating DNA hybridization. MXene acted as both a reductant and stabilizer, significantly improving the electrochemical signal. In addition, the conjugation of PAMAM dendrimer-encapsulated AuNPs and H-DNA worked as an ideal bridge to connect targets and efficient electrochemical tags, providing a high amplification efficiency for the sensing of microRNA-122. A linear relationship between the peak currents and the logarithm of the concentrations of microRNA-122 from 1.0 × 10-2 to 1.0 × 102 fM (I = 1.642 + 0.312 lgc, R2 = 0.9891), is obtained. The detection limit is  0.8 × 10-2 fM (S/N = 3). The average recovery for human serum detection ranged from 97.32 to 101.4% (RSD < 5%).

Enhancing electrochemiluminescence for chloramphenicol detection based on the synergistic effect of doped Ti3C2 with ultrasound.

Chloramphenicol (CAP) is known to be harmful to the environment and food, posing a threat to human health. Developing an effective and convenient method for detecting CAP is crucial. An electrochemiluminescence (ECL) biosensor has been designed for sensitive detection of CAP. The improved ECL behavior was attributed to the synergistic effect of N and P co-doped Ti3C2-Apt1 (N, P-Ti3C2-Apt1) nanoprobes and high intensity focused ultrasound (HIFU) pretreatment. The doping of N and P could improve the electrochemical performance of Ti3C2. HIFU pretreatment generated more reactive oxygen species (ROS) in the luminol-O2 system. N, P-Ti3C2 could aggregate and catalyze ROS, causing an increase in ECL intensity. Furthermore, N, P-Ti3C2 as a carrier loaded more aptamer, which could recognize CAP with high specificity. The detection limit was 0.01 ng/mL. This biosensor has been successfully applied in milk and environmental water samples, highlighting its potential in the field of food and environmental analysis.

Linearly-Changed Thermal Behavior and Depressed Brill Transition in Long-Chain Polyamides Substituted by Methyl Side Groups.

Side substitution is an effective way of functionalizing and modifying the properties of polyamides. Meanwhile, side substitution would significantly influence the crystallization kinetics and polymorphic phase transition of polyamides, which, however, has not been well elucidated. Herein, we synthesized the side-substituted long-chain polyamides with various content of methyl pendent groups and investigated their crystallization and phase transition behaviors. We find that the thermal parameters of side-substituted polyamides vary linearly with the side group content, analogous to the isomorphic crystallization of random copolymers. All the solution-crystallized polyamides experience the α-γ Brill transition during heating, with the Brill transition temperature linearly decreasing as the side group content increases. Intriguingly, the γ-α transition of polyamides during cooling is suppressed with the presence of side methyl groups due to the difficulty in H-bond reorganization and gauche-trans conformational changes. This work has demonstrated the critical role of side substitution in the polymorphic crystallization and phase transition of long-chain polyamides.

An electrochemiluminescence aptasensor based on Ti3C2 QDs-1T/2H MoS2 nano-hybrid material for the highly sensitive detection of lincomycin.

Developing a highly selective and sensitive analysis strategy for lincomycin (LIN) is of great significance for environmental protection and food safety. Herein, we reported a novel electrochemiluminescence (ECL) aptasensor based on Ti3C2 QDs-1T/2H MoS2 nano-hybrid luminophore for detection of LIN. The hybridization of Ti3C2 QDs and 1T/2H MoS2 endowed nanocomposite with structural and compositional advantages for boosting the ECL performance of QDs by about three times. This enhancement could be attributed to the remarkable electrocatalytic activity and high conductivity exhibited by 1T/2H MoS2. Secondly, the great surface area of 1T/2H MoS2 is conducive to the high dispersion of Ti3C2 QDs, and its good conductivity could promote charge transfer. On the other hand, the excellent catalytic performance of 1T/2H MoS2 could facilitate the reduction of S2O82- to produce more radical, which significantly enhance the ECL signal of Ti3C2 QDs. Given these features, a sensor for detection of LIN was established based on specific recognition between target and aptamer. The sensor showed a good linear relationship (0.05 ng mL-1 ∼100 µg mL-1) with a detection limit as low as 0.02 ng mL-1. It is worth noting that this work has been validated in testing milk samples, exhibiting great potential application prospects in food analysis.