Target triggered ultrasensitive electrochemical polychlorinated biphenyl aptasensor based on DNA microcapsules and nonlinear hybridization chain reaction

Ultrasensitive monitoring of PCB77 in environmental samples using a visible-driven photoelectrochemical sensing platform coupling with exonuclease I assisted in target recycling

Due to the urgent need for detecting trace amounts of 3,3',4,4'-tetrachlorobiphenyl (PCB77) in the environment, we have developed an efficient and visible-driven photoelectrochemical (PEC) sensing platform based on carbon quantum dots (CQDs) modified titanium dioxide nanorods (TiO2 NRs), coupling with exonuclease I (Exo I) assisted in target recycling for significant signal amplification. CQDs/TiO2 NRs with high visible-light absorption ability and electron-hole separation efficiency is used as photoactive substrate for anchoring anti-PCB77 aptamer and its complementary DNA (cDNA). With the addition of PCB77, the specific interaction between PCB77 and its aptamer forces aptamer to separate from the electrode surface, resulting in an increase in photocurrent density. Adding Exo I in the test system, a self-catalytic target cycle was motivated, which significantly increased the PEC signal by more than twice, achieving signal amplification. The relationship between the photocurrent density changes and the concentrations of PCB77 are utilized to achieve quantitative detection of PCB77. The designed PEC sensing platform has good analytical performance with a detection limit as low as 0.33 pg L-1, high selectivity and stability. Moreover, the PEC sensor is successfully used to evaluate the content of PBC77 in the environment samples. The established sensing platform provides a simple and efficient method for detecting trace amounts of PCB77 in the environment.

A sensitive electrochemical aptasensor for zearalenone detection based on target-triggered branched hybridization chain reaction and exonuclease I-assisted recycling

Traditional methods for detecting antibiotic and mycotoxin residues rely on large-scale instruments, which are expensive and require complex sample pretreatment processes and professional operators. Although aptamer-based electrochemical sensors have the advantages of simplicity, speed, low cost, and high sensitivity, most aptamer-based sensors lack a signal amplification strategy due to their direct use of aptamers as probes, resulting in insufficient sensitivity. To solve the sensitivity problem in the electrochemical detection process, a novel electrochemical sensing strategy was established for ultrasensitive zearalenone (ZEN) detection on the basis of exonuclease I (Exo I) and branched hybridization chain reaction (bHCR) to amplify the signal. The amplification strategy showed excellent analytical performance towards ZEN with a low detection limit at 3.1×10-12 mol/L and a wide linear range from 10-11 to 10-6 mol/L. Importantly, the assay was utilized in the corn powder samples with satisfactory results, holding promising applications in food safety detection and environmental monitoring.

Perylene diimide-based sensors for multiple analyte sensing (Fe2+/H2S/ dopamine and Hg2+/Fe2+): cell imaging and INH, XOR, and encoder logic

In this report, we present our results on the recognition of multiple analytes using trisubstituted PDI-based chemosensors DNP and DNB in 50% HEPES buffered-CH₃CN solution. Upon the addition of Hg²⁺, DNB showed a decrease and increase in absorbance intensity at 560 and 590 nm, respectively, with a detection limit of 7.17 μM and bleaching of the violet color (de-butynoxy). Similarly, the addition of Fe²⁺ or H₂S to the solution of DNP or DNB resulted in ratiometric changes (A_688nm/A_560nm) with respective detection limits of 185 nM and 27.6 nM for Fe²⁺, respectively, and a color change from violet to green. However, the addition of >37 μM H₂S caused a decrease in absorbance at 688 nm with a concomitant blue shift to 634 nm. Upon the addition of dopamine, the DNP + Fe²⁺ assay showed ratiometric (A_560nm/A_688nm) changes within 10 s along with a color change from green to violet. Moreover, DNP has been successfully used for the exogenous detection of Fe²⁺ in A549 cells. Further, the multiple outputs observed with DNP in the presence of H₂S have been used to construct NOR, XOR, INH and 4-to-2 encoder logic gates and circuits.

Evaluation of the effect of outer primer structure, and inner primer linker sequences, in the performance of Loop-mediated isothermal amplification

Loop-mediated isothermal amplification, or LAMP, is nowadays the most popular isothermal nucleic acid amplification technique. This technique implements a minimum of four primers, named outer (F3/B3) and inner primers (FIP/BIP). The inner primers hybridize in two distinct regions, and some studies have reported that the usage of a linker, typically composed of four thymines, in the middle of these primers can improve assay performance. In addition to this, dual-priming oligonucleotides, DPO, have been reported to provide highly specific reducing non-specific amplifications. Considering the large number of primers implemented in LAMP assays, in the current study the suitability of DPO primers replacing regular outer primers; and their combination with different linker sequences in the inner primers were explored. The results demonstrated that replacing standard F3/B3 by DPO primers does not significantly affect that overall performance of the assay, and provides additional stability to temperature changes. This observations were consistent regardless the type of linker implemented in the inner primers, out of which in the current study a linker composed of thymines significantly outperformed the other options tested, most likely due to a combination of sequence and physical structure.

Biomass-assisted fabrication of rGO-AuNPs as surface-enhanced Raman scattering substrates for in-situ monitoring methylene blue degradation

Reduced graphene oxide-gold nanoparticles nanocomposites (rGO-AuNPs) with high surface-enhanced Raman scattering (SERS) activity was created by biomass-assisted green synthesis with Lilium casa blanca petals biomass for the first time, and its application for methylene blue (MB) degradation was explored through in-situ monitoring. Lilium casa blanca petals biomass was used as a reducing agent to reduce GO and chloroauric acid successively when carrying out rGO-AuNPs in-situ synthesis while it also acted as a capping agent. The produced rGO had oxygen-containing functional groups which had an outstanding performance in enhancing the SERS effect. Characterization results confirmed that the AuNPs were grafted onto the rGO sheet, and the mechanism study showed that total flavonoids in Lilium casa blanca petals biomass were the main biological compounds involved in the reduction. rGO-AuNPs had a high Raman enhancement factor (EF) which could reach 3.88 × 10⁷. The synthesized nanocomposite also had a good catalytic activity that could be employed as catalyst in MB degradation, and it could complete degradation within 15min. The reaction rate increased linearly with the amount of rGO-AuNPs, and the degradation could be in-situ monitored both by UV and SERS.

Simple Monovalent Metal Ion Logical Order to Regulate the Secondary Conformation of G-Quadruplex

Based on the reactions of different sequences with single ions K⁺, Na, NH₄ ⁺, double ions high + low, low + high, and triple ions with different addition orders, the best stable ion combinations of 12 quadruplexes with different DNA sequences were reported. From the fluorescence spectrum, except for HT-V15 and PW17 and AS1411 and HT-V18, the structural stability of G-quadrangle formed basically follows a certain rule. In terms of this experiment, according to circular dichroism, the antiparallel quadrupole structure has the largest proportion among quadrupole structures, and 12 optimal DNA addition schemes and sequences have been obtained through exploration. It is worth mentioning that, on the whole, the best addition scheme of AS1411 and HT-V18 is a three-ion scheme, which provides an effective reference for similar experiments in the future.

Highly Stretchable and Sensitive Flexible Strain Sensor Based on Fe NWs/Graphene/PEDOT:PSS with a Porous Structure

With the rapid development of wearable smart electronic products, high-performance wearable flexible strain sensors are urgently needed. In this paper, a flexible strain sensor device with Fe NWs/Graphene/PEDOT:PSS material added under a porous structure was designed and prepared. The effects of adding different sensing materials and a different number of dips with PEDOT:PSS on the device performance were investigated. The experiments show that the flexible strain sensor obtained by using Fe NWs, graphene, and PEDOT:PSS composite is dipped in polyurethane foam once and vacuum dried in turn with a local linearity of 98.8%, and the device was stable up to 3500 times at 80% strain. The high linearity and good stability are based on the three-dimensional network structure of polyurethane foam, combined with the excellent electrical conductivity of Fe NWs, the bridging and passivation effects of graphene, and the stabilization effect of PEDOT:PSS, which force the graphene-coated Fe NWs to adhere to the porous skeleton under the action of PEDOT:PSS to form a stable three-dimensional conductive network. Flexible strain sensor devices can be applied to smart robots and other fields and show broad application prospects in intelligent wearable devices.

Translating cancer exosomes detection into the color change of phenol red based on target-responsive DNA microcapsules

Emerging evidence indicates that exosomes can be used as a potential biomarker for monitoring diseases, including cancer. However, enhancing the sensing performance in terms of convenience and sensitivity remains an urgent demand for exosomes detection. In this study, a pH-sensitive colorimetric biosensing strategy was developed for exosomes detection by integrating stimuli-responsive DNA microcapsules and acetylcholinesterase to produce acetic acid. The constructed DNA microcapsules consisted of DNA shells crosslinked by anti-CD63 aptamers and loaded with acetylcholinesterase. With exosomes addition, an energetically stabilized aptamer-CD63 compound was produced and microcapsules dissociated due to the reaction of surface protein CD63 of exosomes and aptamer of CD63, resulting in the release of encapsulated AChE. Through a simple centrifugation separation, unreacted DNA microcapsules were removed and the supernatant containing released acetylcholinesterase collected, which was then used for colorimetric exosomes detection through the ability of acetylcholinesterase to hydrolyze acetylcholine to release acetic acid. The resulting decreased solution pH was detected with phenol red indicator, with the sharp color transition conveniently by naked eye. Exosomes quantification was also achieved using the solution's absorption intensity ratio of 558 vs. 432 nm. The linear range was from 2.0 × 10³ to 5.0 × 10⁵ particles/μL, and the limit of detection and limit of quantification were 1.2 × 10³ particles/μL and 2.2 × 10³ particles/μL, respectively. In addition, this proposed strategy for exosomes detection showed a relative standard deviation of 3.1% and high recovery efficiency (>94%), exhibiting a bright application future in exsomes analysis.

Bio-nanocapsules for oriented immobilization of DNA aptamers on aptasensors

The oriented immobilization of sensing molecules (e.g., IgGs, receptors, lectins, and DNA aptamers) on sensor chips is particularly important for maximizing the potential of the sensing molecules, thereby enhancing the sensitivity and target-binding capacity of biosensors. We previously developed ∼30 nm bio-nanocapsules (ZZ-BNCs) consisting of the hepatitis B virus envelope L protein fused with the tandem form of protein A-derived IgG Fc-binding Z domain (ZZ-L protein). ZZ-BNC acts successfully as a scaffold, enhancing both the sensitivity and binding capacity of IgG, a Fc-fused receptor, and Fc-fused lectin to antigens, cytokines, and sugar chains through an oriented immobilization on a biosensor surface. To expand the versatility of ZZ-BNC, we modified ZZ-BNC by replacing the ZZ domain with a DNA-binding single-chain lambda Cro (scCro) domain, thereby developing scCro-BNC. The scCro-BNC was synthesized in yeast cells and homogeneously purified as ∼30 nm sized nanoparticles. In a quartz crystal microbalance, an scCro-BNC-coated sensor chip immobilized with thrombin-binding DNA aptamers showed an ∼5.5-fold higher thrombin-binding capacity and ∼6000-fold higher detection sensitivity than a sensor chip directly coated with DNA aptamers. In addition, the number of bound thrombin molecules per molecule of DNA aptamer increased by ∼7.8-fold with an scCro-BNC coating, consistent with the theoretical thrombin-binding capacity. Collectively, scCro-BNC was shown to perform as an ideal scaffold for maximizing the potential of the DNA aptamer by immobilizing it in an oriented manner. Facilitating a highly sensitive detection of various target molecules, these BNC-based scaffolds are expected to improve a wide range of biosensors while minimizing the number of sensing molecules required.

Bifunctional monomer oligomers-based composite molecularly imprinted membranes for the electrochemical monitoring of Sudan I

P(L)ICO and PASCO-independent bifunctional monomer oligomers were utilized to construct a molecularly imprinted electrochemical sensor for monitoring Sudan I.

Nonlinear hybridization chain reaction-based functional DNA nanostructure assembly for biosensing, bioimaging applications

Hybridization chain reaction (HCR) can be divided into two categories: linear HCR and nonlinear HCR. In traditional linear HCR, the relatively slow kinetics and less sufficient sensitivity largely limit its scope of application. In the nonlinear HCR system, under the trigger of the initiator, the judicious designed substrate sequences (hairpin or hairpin-free) will self-assembly to dendritic or branched DNA nanostructures with exponential growth kinetics. Given the advantages of its enzyme-free, high-order growth kinetic, high sensitivity, and simple operation, nonlinear HCR is regarded as a powerful signal amplifier for the detection of biomarkers by integrating with versatile sensing platforms in the past few decades. In this review, we describe the basic features of nonlinear HCR mechanism and classify the nonlinear HCR into several categories based on their self-assembly mechanisms: the branched HCR, dendritic HCR, hydrogel-based clamped HCR, and other types of HCR. Then, we summarize the recent development of nonlinear HCR in biosensing, such as nucleic acid, protein, enzyme activities, and cancer cell detection, etc., and we also review the current applications of nonlinear HCR in bioimaging (mRNA in situ imaging). We choose several representative works to further illustrate the analysis mechanisms via various detection platforms, such as fluorescence, electrochemical, colorimetric, etc. At last, we also review the challenges and further perspectives of nonlinear HCR in the use of bioanalysis.

The Recent Development of Hybridization Chain Reaction Strategies in Biosensors

With the continuous development of biosensors, researchers have focused increasing attention on various signal amplification strategies to pursue superior performance for more applications. In comparison with other signal amplification strategies, hybridization chain reaction (HCR) as a powerful signal amplification technique shows its certain charm owing to nonenzymatic and isothermal features. Recently, on the basis of conventional HCR, this technique has been developed and improved rapidly, and a variety of HCR-based biosensors with excellent performance have been reported. Herein, we present a systematic and critical review on the research progress of HCR in biosensors in the last five years, including the newly developed HCR strategies such as multibranched HCR, migration HCR, localized HCR, in situ HCR, netlike HCR, and so on, as well as the combination strategies of HCR with isothermal signal amplification techniques, nanomaterials, and functional DNA molecules. By illustrating some representative works, we also summarize the advantage and challenge of HCR in biosensors, and offer a deep discussion of the latest progress and future development trends of HCR in biosensors.