Lei Ge

Layered Double Hydroxide Functionalized Textile for Effective Oil/Water Separation and Selective Oil Adsorption

The removal of oil and organic pollutants from water is highly desired due to frequent oil spill accidents, as well as the increase of industrial oily wastewater. Here, superhydrophobic and superoleophilic textile has been successfully prepared for the application of effective oil/water separation and selective oil adsorption. This textile was fabricated by functionalizing the commercial textile with layered double hydroxide (LDH) microcrystals and low surface energy molecules. The LDH microcrystals were immobilized on the microfibers of the textile through an in situ growth method, and they formed a nestlike microstructure. The combination of the hierarchical structure and the low surface energy molecules made the textile superhydrophobic and superoleophilic. Further experiments demonstrated that the as-prepared textile not only can be applied as effective membrane materials for the separation of oil and water mixtures with high separation efficiency (>97%), but also can be used as a bag for the selective oil adsorption from water. Thus, such superhydrophobic and superoleophilic textile is a very promising material for the application of oil spill cleanup and industrial oily wastewater treatment.

Affinity-Mediated Homogeneous Electrochemical Aptasensor on a Graphene Platform for Ultrasensitive Biomolecule Detection via Exonuclease-Assisted Target-Analog Recycling Amplification

As is well-known, graphene shows a remarkable difference in affinity toward nonstructured single-stranded (ss) DNA and double-stranded (ds) DNA. This property makes it popular to prepare DNA-based optical sensors. In this work, taking this unique property of graphene in combination with the sensitive electrochemical transducer, we report a novel affinity-mediated homogeneous electrochemical aptasensor using graphene modified glassy carbon electrode (GCE) as the sensing platform. In this approach, the specific aptamer-target recognition is converted into an ultrasensitive electrochemical signal output with the aid of a novel T7 exonuclease (T7Exo)-assisted target-analog recycling amplification strategy, in which the ingeniously designed methylene blue (MB)-labeled hairpin DNA reporters are digested in the presence of target and, then, converted to numerous MB-labeled long ssDNAs. The distinct difference in differential pulse voltammetry response between the designed hairpin reporters and the generated long ssDNAs on the graphene/GCE allows ultrasensitive detection of target biomolecules. Herein, the design and working principle of this homogeneous electrochemical aptasensor were elucidated, and the working conditions were optimized. The gel electrophoresis results further demonstrate that the designed T7Exo-assisted target-analog recycling amplification strategy can work well. This electrochemical aptasensor realizes the detection of biomolecule in a homogeneous solution without immobilization of any bioprobe on electrode surface. Moreover, this versatile homogeneous electrochemical sensing system was used for the determination of biomolecules in real serum samples with satisfying results.

A versatile immobilization-free photoelectrochemical biosensor for ultrasensitive detection of cancer biomarker based on enzyme-free cascaded quadratic amplification strategy.

In this work, an ultrasensitive immobilization-free photoelectrochemical (PEC) biosensor was successfully developed for the first time based on a novel enzyme-free cascaded quadratic signal amplification strategy. This rationally designed homogeneous dual amplification strategy consists of a target-analog recycling circuit based on catalytic hairpin assembly (CHA) and a hybridization chain reaction (HCR) mediated amplification circuit. In the presence of carcinoembryonic antigen (CEA), a proof-of-concept target, target-analog is released to trigger the upstream CHA recycling circuit. The generated dsDNA complexes from CHA recycling could further induce the downstream HCR amplification, leading to the formation of numerous hemin/G-quadruplex DNAzymes. This would accordingly stimulate the biocatalytic precipitation of 4-chloro-1-naphthol, inducing a distinct decrease in the photocurrent signal due to the formed insoluble/insulating products on electrode surface. Under the optimal conditions, this PEC biosensor achieved ultrasensitive detection of CEA down to the atto-gram level. The introduction of this aptamer-based cascaded quadratic amplification strategy not only remarkably improves the selectivity and sensitivity of CEA assay, but also allows the ultrasensitive detection of other proteins by designing specific aptamers, providing a universal, isothermal and label-free PEC biosensing platform for ultrasensitive detection of different kinds of cancer biomarkers and holding a great potential for early-diagnosis of cancer.

Graphene-Assisted Label-Free Homogeneous Electrochemical Biosensing Strategy based on Aptamer-Switched Bidirectional DNA Polymerization

In this contribution, taking the discrimination ability of graphene over single-stranded (ss) DNA/double-stranded (ds) DNA in combination with the electrochemical impedance transducer, we developed a novel label-free homogeneous electrochemical biosensor using graphene-modified glassy carbon electrode (GCE) as the sensing platform. To convert the specific aptamer-target recognition into ultrasensitive electrochemical signal output, a novel aptamer-switched bidirectional DNA polymerization (BDP) strategy, capable of both target recycling and exponential signal amplification, was compatibly developed in this study. In this strategy, all the designed DNA structures could be adsorbed on the graphene/GCE and, thus, serve as the electrochemical impedance signal reporter, while the target acts as a trigger of this BDP reaction, in which these designed DNA structures are bound together and, then, converted to long dsDNA duplex. The distinct difference in electrochemical impedance spectroscopy between the designed structures and generated long dsDNA duplex on the graphene/GCE allows label-free and homogeneous detection of target down to femto-gram level. The target can be displaced from aptamer through the polymerization to initiate the next recognition-polymerization cycle. Herein, the design and signaling principle of aptamer-switched BDP amplification system were elucidated, and the working conditions were optimized. This method not only provides a universal platform for electrochemical biosensing but also shows great potential in biological process researches and clinic diagnostics.

Ratiometric Catalyzed-Assembly of NanoCluster Beacons: A Nonenzymatic Approach for Amplified DNA Detection

In this work, a novel fluorescent transformation phenomenon of oligonucleotide-encapsulated silver nanoclusters (AgNCs) was demonstrated, in which green-emissive AgNCs effectively transformed to red-emissive AgNCs when placed in close proximity to a special DNA fragment (denoted as convertor here). Taking advantage of a catalyzed-hairpin-assembly (CHA) amplification strategy, we rationally and compatibly engineered a simple and sensitive AgNC-based fluorescent signal amplification strategy through the ratiometric catalyzed-assembly (RCA) of green-emissive NanoCluster Beacon (NCB) with a convertor modified DNA hairpin to induce the template transformation circularly. The proposed ratiometric fluorescent biosensing platform based on RCA-amplified NCB (RCA-NCB) emits intense green fluorescence in the absence of target DNA and will undergo consecutively fluorescent signal transformation from green emission to red emission upon exposure to its target DNA. The ratiometric adaptation of the NCB to CHA circuit advances their general usability as biosensing platform with great improvements in detection sensitivity. By measuring the fluorescence intensity ratio of the red emission and green emission, the proposed RCA-NCB platform exhibits sensitive and accurate analytical performance toward Werner Syndrome-relevant gene, the proof-of-concept target in this work. A low detection limit down to the pM level was achieved, which is lower than most of the reported AgNC-based fluorescent DNA biosensors, making the proposed RCA-NCB biosensing strategy appealing in amplifying the ratiometric fluorescent signal for sensitive DNA detection. Moreover, our proposed RCA-NCB platform shows good recovery toward the target DNA in real human serum samples, illustrating their potential promise for clinical and imaging applications in the future.

Unique quenching of fluorescent copper nanoclusters based on target-induced oxidation effect: a simple, label-free, highly sensitive and specific bleomycin assay

In this contribution, a novel label-free fluorescence biosensor for bleomycin (BLM) detection was developed by combining the excellent fluorescence properties of copper nanoclusters (CuNCs) and the unique oxidation capability of a BLM–Fe2+ complex toward CuNCs. The CuNCs probe was prepared through in situ formation of CuNCs using single-stranded DNAs as the templates, endowing the probe with good water-dispersibility that is important for analyzing biological samples. After their recognition of BLM, the CuNCs were destroyed and the red fluorescence of the probe was quenched, thus realizing the detection of BLM. Such a fluorescence sensing strategy allows for highly sensitive BLM biosensing with a detection limit as low as 0.26 nM and minimal interference from complex mixtures. Compared to previously reported methods, the as-proposed assay does not need specific DNA sequences, complex designing or signal molecule labeling, and further avoids tedious experimental procedures, thus providing the strategy with additional advantages of simplicity and cost-effectiveness. Furthermore, our probe was also adopted for the detection of BLM in human serum samples and excellent performance was achieved, which makes the as-proposed strategy a promising candidate for highly sensitive and specific analysis of BLM in cancer treatment.

Electro-Grafted Electrode with Graphene-Oxide-Like DNA Affinity for Ratiometric Homogeneous Electrochemical Biosensing of MicroRNA

This work demonstrated for the first time a simple and rapid approach to endow the electrode with the excellent discrimination ability over single-stranded DNA (ssDNA) and double-stranded DNA (dsDNA) through the robust electrochemical grafting of in situ generated 1-naphthalenesulfonate (NS-) diazonium salt onto the surface of indium tin oxide (ITO) electrode. On the basis of understanding the influence of sequence and length on the binding affinity of ssDNA and dsDNA toward NS- grafted ITO (NS--ITO) electrode, these interesting findings were successfully employed to rationally develop a ratiometric homogeneous electrochemical biosensing platform for microRNA based on the affinity-mediated signal transduction. The achievement of ultrasensitive detection of microRNA lies in a compatibly designed T7 exonuclease-assisted isothermal amplification strategy, in which the presence of target microRNA initiated the continual and opposite affinity inversion of two rationally engineered electrochemical signal reporters, methylene blue (MB) labeled hairpin reporter and ferrocene (Fc) labeled dsDNA reporter, toward NS--ITO electrode, thereby providing the ratiometric transduction and amplification of the homogeneous electrochemical output signal. By measuring the distinct variation in the peak current intensity ratios of Fc and MB tags, this ratiometric homogeneous electrochemical microRNA biosensing platform showed a detection limit of 25 aM, which is much lower than that of the reported homogeneous electrochemical biosensors. Therefore, we envision that the proposed approach will find useful applications in disease molecular diagnoses and biomedicine.

Oligonucleotide-modulated photocurrent enhancement of a tetracationic porphyrin for label-free homogeneous photoelectrochemical biosensing

This work reports the first demonstration of an oligonucleotide-modulated label-free homogeneous photoelectrochemical (PEC) biosensing platform based on the adsorption of tetracationic porphyrin (denoted as TMPyP here) onto 1-naphthalenesulfonate anion (NS-)-grafted indium tin oxide electrode (denoted as TMPyP-NS--ITO), which generates a stable and rapid photocurrent response. We found that when NS--ITO electrode was subjected to single-stranded oligonucleotide (ssON) before TMPyP adsorption, a remarkable enhancement of photocurrent intensity was observed from the resulted TMPyP-ssON-NS--ITO electrode with high specificity towards oligonucleotide. A series of investigations were carried out to understand the mechanism of this oligonucleotide-modulated photocurrent enhancement phenomenon. Moreover, the studies of this robust photocurrent enhancement mechanism was successfully extended to develop a signal-on homogeneous PEC biosensing platform for, as a proof-of-concept, label-free M.SssI methyltransferase activity analysis through a judiciously and compatibly engineered signal transduction strategy consisted of hairpin-shaped oligonucleotide probe, restriction endonuclease HpaII, and Exonuclease I. The rationally designed homogeneous PEC biosensor exhibit sensitive PEC response toward M.SssI methyltransferase with a low detection limit of 3.5 mU/mL and a wide linear range from 0.01 to 120 U/mL. Additionally, we show that our homogeneous PEC biosensing platform can be also utilized to screen methyltransferase inhibitors. Therefore, this work will provide a distinctive paradigm for versatile homogeneous PEC biosensing platform that can be used as potential powerful tool toward innovative label-free bioanalytical purposes.