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There still exists a resplendent prospect of developing a robust and stable non-noble metal catalyst for overall water splitting. Herein, we designed highly efficient amorphous FeMn-based electroca...

The use of a Schlenk line (SL) promotes a strategy involving N-butyllithium for the chemical exfoliation of layered crystals, with the remarkable merits of being low risk and allowing “one-pot” operation. Significantly, metallic-phase and defect-abundant nanosheets are synthesized from SL-exfoliated molybdenum disulphide (SL-MoS2), exhibiting the desired morphological features with a high percentage of monolayers and uniform planar size. Additionally, SL-MoS2 has the excellent structural features of a metallic phase and abundant defects, thereby supporting high activity during the electrocatalytic hydrogen evolution reaction (HER). Nevertheless, the unique structural and morphological characteristics of SL-MoS2 are proved to cause the rapid dissociation of the SL-MoS2 nanosheets in H2O2-rich environments, and the electrocatalytic performance accordingly declines. The HER current density, which is dependent on the number of active sites of SL-MoS2, specifically reflects the reactive-oxygen-species-based degradation of the SL-MoS2 nanoprobes; this can contribute to the electrochemical monitoring of enzyme-associated biological targets and processes using developed chips based on SL-MoS2-modified carbon fibers.

The requirement of hydrogen adsorption Gibbs free energy (ΔGH*) approximating to 0 eV limits the hydrogen evolution reaction (HER) activity of most electrocatalysts in alkaline media. The construction of interface and defects engineering is an effective strategy to obtain the optimal ΔGH*. Ni3N exhibits poor HER activity due to its undesirable ΔGH*. By cooperating with Nb2O5, the d-band center of Ni3N was reduced, improving its catalytic performance. The optimized Nb2O5–Ni3N displays an overpotential of 80 mV at 10 mA cm−2 and superior activity than the benchmark Pt/C catalyst when the current density is greater than 125 mA cm−2. Experimental and density functional theory results demonstrate that the improved catalytic activity is because the electronic interaction between Ni and Nb changes the coordination numbers of these two atoms, resulting in oxygen vacancies at the interface. Under the synergistic effect of Nb2O5 and Ni3N, the catalyst exhibits optimal ΔGH* and water adsorption energy.

Mimic enzymes greatly improve the inherent insufficiencies of natural enzymes. Therefore, mimic enzyme sensors attract increasing research interest. Metal-organic framework (MOF) is emerging in the field of mimic enzyme catalysis due to its remarkable structural properties. In this paper, a colorimetric method is designed for rapid and sensitive detection of glucose and cysteine levels. The MOF Eu-pydc (pydc—2,5-pyridinedicarboxylic acid) is synthesized by a new strategy which is regulated by ligands at room temperature and found to have peroxidase activity. Then, the MOF is used as a mimic enzyme to catalyze chromogenic substrate (3,3′,5,5′-tetramethylbenzidine, TMB) for colorimetric sensing of glucose. The developed method can accurately detect glucose in the range of 10 μM–1 mM (R2 = 0.9958) with a relatively low detection limit about 6.9 μM. Moreover, a cysteine sensor with a detection limit of 0.28 μM is also established based on the disappearance of the color of oxTMB. Additionally, the proposed glucose sensor exhibits excellent selectivity and is successfully applied to blood glucose detection. At the same time, the detection of cysteine is also highly sensitive. In short, the dual sensor is fast, low cost, and convenient, and has great application potential in the diagnosis of disease.

Exploring high active, durable, and earth-abundant electrocatalysts for sustainable hydrogen production is a necessary prerequisite of the future hydrogen economy. Herein, anion-regulation of 3D fl...

Ratiometric assays, which can effectively surmount external interference, have attracted extensive research interests. Herein, a novel ratiometric sensing platform for Hg2+ is designed based on nitrogen-doped carbon dots (N-CDs) with two different optical signals. Under a single excitation, N-CDs have two emission peaks around 668 nm and 412 nm, which are second-order scattering and fluorescence, respectively. Upon the addition of Hg2+, the weak scattering emission at 668 nm can be increased apparently, while the strong fluorescence intensity at 412 nm is weakened. Moreover, the ratio of scattering intensity to fluorescence intensity is linearly dependent on Hg2+ concentration (0.1–10 μM and 10–30 μM, respectively), and the detection limit is 66 nM. In addition, the ratiometric sensing mechanism is investigated in detail, which is due to the combined effect of aggregation-induced fluorescence quenching and scattering enhancement. Furthermore, the developed sensing approach holds a promising application for Hg2+ detection in actual samples.

Herein, we have synthesized successfully a three-dimensional/two dimensional (3D/2D) core–shell Cu2O@Fe–Ni3S2 nanoflower on copper foam at room temperature. Remarkably, by virtue of rich active sites and vacancies, large surface area, high conductivity and close contact with the electrolyte, the Cu2O@Fe–Ni3S2 catalyst exhibits superior stability and oxygen evolution reaction performance.

Developing novel luminescent materials for sensitive and rapid detection of phosphate (Pi) is vital in clinical diagnoses and water-quality monitoring. Herein, a lanthanide coordination polymer (NH2-BDC–TbGMP CPs)-based ratiometric fluorescent probe is designed for quick and visual detection of Pi. The NH2-BDC–TbGMP CPs are prepared via the self-assembly of 2-aminoterephthalic acid (NH2-BDC) and guanine monophosphate (GMP) with terbium ions (Tb3+). After the formation of NH2-BDC–TbGMP CPs, the inherent fluorescence of NH2-BDC is quenched via static quenching, while the nonluminous Tb3+ can emit strong green fluorescence due to the antenna effect between Tb3+ and GMP. In the presence of Pi, Pi can competitively combine with Tb3+ to interrupt the interaction of the NH2-BDC–TbGMP CP system, further causing a decrease in the fluorescence of Tb3+ and an increase in the emission of NH2-BDC. Accordingly, the ratiometric fluorescence sensing of Pi can be achieved by continuously recording the variations of two fluorescence signals. The corresponding fluorescence intensity ratio of Tb3+ to NH2-BDC (F547/F425) is linearly correlated with the Pi concentration in the range of 0.5 to 100 μM, with a detection limit of 0.13 μM. This strategy offers a simple, rapid, and sensitive method for the ratiometric fluorescence and visual sensing of Pi, which shows great application potential for water-quality monitoring.

Layered nanostructures (LNs), including two-dimensional nanosheets, nanoflakes, and planar nanodots, show large surface-to-volume ratios, unique optical properties, and desired interfacial activities. LNs are highly promising as alternative probes and platforms due to numerous merits, e.g. signal amplification, improved recognition ability, and anti-interference capacity, for emerging sensing applications. Significantly, when stimuli-responsive aggregation occurs, the modified LNs show engineered morphologies, attractive optical absorption and fluorescence characteristics, which are remarkably programmable. On the basis of the altered aggregation behaviours of LNs, as well as their modulated physical and chemical characteristics, a series of novel sensing assays exhibiting enhanced sensitivity, simple operation, multiple functions, and improved anti-interference capacity are reported, contributing to both point-of-care testing and high-throughput measurements. Herein, the aggregation-induced response sensing strategies of LNs are comprehensively summarized with the classification of materials and variation of aggregated routes aiming at understanding dimension-dependent features, expanding nanoscale biosensor applications, and addressing key issues in disease diagnosis and environmental analysis.

Highly active, earth-abundant, and stable electrocatalysts are indispensable for overall water splitting. In this work, hierarchical dendrite-like Co0.75Ni0.25 alloy prepared by a simple hydrothermal reduction route can serve as a high-performance catalyst for hydrogen evolution reaction. The synergistic effect from Co and Ni atoms optimizes the catalytic behavior of their alloy, and the hierarchical dendrite structure enlarges the contact area with the electrolyte, exposing more active sites. Based on the dendrite-like Co0.75Ni0.25 alloy, we further fabricate a core-shell architecture with the conductive N-doped carbon shell coated dendrite-like CoNi/CoNiO2 nanocomposites via a calcination process at 600 ℃ (CoNi/CoNiO2@NC-600). The dendrite-like CoNi/CoNiO2@NC-600 displays significantly improved activity of oxygen evolution reaction due to large active surface area, high conductivity, and the continuous electron transfer among metal, metal oxide, and N-doped carbon. Furthermore, the dendrite-like Co0.75Ni0.25 alloy and CoNi/CoNiO2@NC-600 are assembled into a water splitting electrolyzer with a low voltage of 1.51 V to drive a current density of 10 mA cm−2.

On-site monitoring of hazardous nitroaromatic explosive 2,4,6-trinitrophenol (TNP) is of great significance. In this work, we develop a bionic electronic eye-integrated dual-channel nanosensor to rapid and accurate quantification of TNP just via a smartphone. The sensing platform is composed of g-CQDs as the TNP-response recognition element and a smartphone as the optical signal detector, possessing simplicity, rapidness, and portability for TNP tracing. The transducer is based on novel green-emitting fluorescent carbon quantum dots (g-CQDs), which display color and fluorescence dual-signal response towards TNP. Under the optimum conditions, the color and fluorescence intensity change linearly with the increase of the TNP concentration in the range of 1.1–19.8 μM and 0.1–15.8 μM with a low detection limit of 0.4 μM and 27 nM, respectively. It is the inner filter effect that results in the sensitive fluorescence and color switch of CQDs by TNP. Also, the proposed sensor shows excellent selectivity towards TNP, because only TNP can compete for the excitation light with CQDs. Furthermore, the sensing platform is successfully employed to rapid, sensitive, and visual pH monitoring, fulfilling its bifunctional applications. Therefore, the smartphone-integrated dual-mode detection system is promising to be a new portable detector for on-site TNP and pH analysis.

Ammonia concentration together with pH values are important and closely linked indexes for aqueous systems. Rapid on-site determination of ammonia or pH is of great significance to environmental monitoring. In this work, a pH-switchable nanoprobe based on biomass carbon dots (CDs) is developed using a smartphone as a simple and handy instrument. The CDs demonstrate sensitive pH response in wide linear ranges of 6.1–13.6, and 2.0–13.6 with colorimetric and fluorescent channels, respectively. It is the pH-induced aggregation that governs the color and fluorescence switch. With the pH evolution caused by the dissolution of ammonia, the smartphone-integrated nanoprobe is applied to ammonia detection with a broad range of 0.5–300 mM. Moreover, the headspace single drop microextraction strategy can concentrate ammonia from matrix, offering a remarkably high selectivity for ammonia determination. Finally, the practical applications of this method for ammonia analysis obtained satisfactory results.

Dye sensitization achieving photoelectrochemical (PEC) signal amplification for ultrasensitive bioanalysis has undergone a major breakthrough. In this proposal, an innovative PEC sensing platform is developed by combining Z-scheme WO3@SnS2 photoactive materials and a G-wire superstructure as well as a dye sensitization enhancement strategy. The newly synthesized WO3@SnS2 heterojunction with outstanding PEC performance is employed as a photoelectrode matrix. Due to the formation of the Z-scheme heterojunction between WO3 and SnS2, the migration dynamics of the photogenerated carrier is evidently augmented. To improve sensitivity, the target excision-driven dual-cycle signal amplification strategy is introduced to output exponential c-myc fragments. Crystal violet is then conjugated into the G-quadruplex to amplify the PEC signal, where crystal violet generates excited electrons by capturing visible light and rapidly injects electrons into the conduction band of SnS2, suppressing the recombination of the photo-induced carrier. Moreover, the G-wire superstructure acts as a universal amplification pathway, ensuring adequate crystal violet loads. Specifically, the biosensor for uracil-DNA glycosylase quantification displays a wide detection range (0.0005-1.0 U/mL) and a lower detection limit (0.00025 U/mL). Furthermore, the Z-scheme electron migration mechanism and the crystal violet sensitization effect are discussed in detail. The construction of the PEC sensor provides a new consideration for signal amplification and material design.

Esterase activity is often used as an index to evaluate the health status of cells and plays an important role in cell metabolism and apoptosis. Herein, we develop two fluorescent probes for visual biosensing of esterase activity and imaging in living cells. In vitro, after the introduction of esterase, enzymolysis destroys the ester bond of the probe, causing the fluorescent color of probe changes from yellow to red, thus realizing the visual strategy for determination of esterase activity, with high sensitivity and selectivity. Especially, probe VA, 2-(4-acetoxystyryl)-3-ethyl-1,1-dimethyl- 1H-benzo[e]indol-3-ium, exhibits higher sensitivity with a lower detection limit (up to 7.15 × 10-6 U/mL). In the cell experiment, the fluorescent probe VA also shows good biocompatibility and high spatial resolution, and is successfully applied to the intracellular fluorescent imaging and biosensing of esterase in living cells. More importantly, the probe VA can judge the unhealthy state of H2O2-induced HeLa cells using dual-fluorescence signals. The results confirm that the fluorescence method is a reliable tool for detecting endogenous esterase in living biological system.

Defects in layered semiconductors cause large variation of electric and catalysis properties, and exploiting defect-involved reaction can deeply excavate unearthed characteristics with significant performances. Mo-terminated defects of MoS2 spontaneously guide the oriented growths of ultrasmall Au nanocrystals on specific sites of liquid-exfoliated (LE) nanosheets, which are experimentally and theoretically performed with programmable heterostructures. The conjugated construction of Au plasmonics and MoS2 semiconductors is manipulated with the aim of the optimal synergistic activity. Additionally, with photonic irradiation, hot electrons excited from attached plasmonic nanostructures are injected into MoS2 semiconductors, which remarkably increases the carrier density of catalyst to match the energy level of hydrogen evolution reaction (HER). Obeying the principle of proximity, localized MoS2 defect-adjacent Au plasmonics exhibit a more valid pathway, transferring hot electrons from donators to receptors of catalytic sites, in comparison to planar Au decoration. Meanwhile, Au nanostructures located at basal planes are essential for accelerated electron transport rates between catalysts and electrodes, and high stabilities in plasmonic-motivated electrocatalytic performances are guaranteed. The dual function of location-discriminated Au nanostructures accounts for superior electrocatalytic HER performances with photonic excitation, which imparts high inspiration in expanded heterostructures and integrated plasmonic techniques for catalysis and devices.

Glutathione (GSH) plays a critical role in the living system and its abnormalities are closely associated with numerous clinical diseases. Thus, monitoring and detecting the content of GSH in the living system is still of great importance. Herein, a novel dual-signal responsive optical sensor is developed by using resonance Rayleigh scattering (RRS) and colorimetry for sensitive detection of GSH. In this sensor, MnO2 nanoflakes are used as both GSH recognizer and signal transducer of RRS and colorimetry. The solution of MnO2 nanoflakes shows strong RRS and absorption signals because MnO2 nanoflakes possess a large surface area and high molar extinction coefficient. However, MnO2 can be reduced to Mn2+ and MnO2 nanoflakes can be etched to small nanoparticles by GSH, causing both the RRS and absorption signals to decrease. Based on the change of RRS signal and absorbance of MnO2 nanoflakes, a novel dual-signal responsive optical sensor is successfully constructed to detect the content of GSH. The as-developed optical sensor toward GSH presents a favorable sensitivity with a detection limit of 0.033 and 0.67 μM for RRS and colorimetry, respectively. Furthermore, the as-developed approach is straightforward, quickly responsive, free-label, and cost-effective. More significantly, this method combines the advantages of RRS and colorimetry for the detection of GSH. Beyond this, the proposed RRS method has also been successfully utilized to detect the content of GSH in glutathione injection samples.

The visible-light photoactive heterostructures with effective carrier transformation and desirable material properties have caught more and more researchers’ attention in recent years. Herein, a photoelectrochemical sensing platform is constructed based on Fe2O3@Bi2S3 heterostructure for an enzymatic process and enzyme activity inhibition assay. In the proposal, the amount of Fe2O3 in Fe2O3@Bi2S3 sample was optimized firstly. Specifically, the photocurrent intensity of Fe2O3@Bi2S3 heterostructure is gradually enhanced with proper introduction of Fe2O3. Moreover, the Fe2O3@Bi2S3 heterostructure is first used to design the sensing via hydrolytic reaction and enzyme activity inhibition reaction. When loaded on the substrate of Fe2O3@Bi2S3 with the help of gold nanoparticles, alkaline phosphatase (ALP) can hydrolyze l -ascorbic acid 2-phosphate trisodium salt to produce ascorbic acid in situ, consequently achieving the enzymatic process. In the second place, the constructed sensing is employed to detect the inhibitor of sodium fluoride for ALP, which is closely associated with enzyme activity and human health problems. The ingenious designed sensing presents an outstanding linearity for the detection of sodium fluoride, and the concentration varies from 0.01 to 1000 μM. The integration of heterostructure and photoelectrochemical technique demonstrates an innovative methodology for the assay of biological targets. Furthermore, the designed strategy can greatly enhance the analytical performance and thus provides a novel method for the high selective and sensitive detection of chemicals.

Developing the cost-effective catalyst based on earth-abundant materials is a crucial demand for water oxidation. Doping heteroatom into catalysts is regarded as an effective strategy to regulate electronic configuration and improve the catalytic performance of water oxidation. In this work, N-doped CoS2 on carbon cloth is fabricated by one-step synthesis, in which thiourea acts as both sulfur and nitrogen sources. The N-doped cobalt disulfide shows superior catalytic activity for oxygen evolution, with a low overpotential of 240 mV for 10 mA cm−2, small Tafel slope (56 mV dec−1) and high turnover frequency due to the modification with electronic structure after incorporation of N atom. Moreover, the incorporation of N atom provides a distinctive perspective of doping other heteroatom into the material for modifying the electrochemical properties.

Ratiometric sensing suffers from less interference and can obtain more accurate results than single-signal assay. Here, a new ratiometric optical sensing strategy for H2O2 detection is developed by etching silver nanoparticles (AgNPs) to deactivate fluorescence resonance energy transfer (FRET) and reduce Rayleigh scattering based on a hyphenated technique of fluorescence and second-order Rayleigh scattering (SRS). The ratiometric detection of H2O2 is achieved through exploiting a hybrid system fabricated by fluorescent carbon dots and silver nanoparticles (CDs/AgNPs). In the CDs/AgNPs system, the fluorescence of CDs is quenched because of FRET, and the scattering is strong due to the intrinsic high light-scattering power of AgNPs. With the introduction of H2O2, the AgNPs are etched and the CDs are released from the AgNP surface, resulting in the fluorescence enhancement and scattering decline. As a result, ratiometric sensing of H2O2 can be achieved based on the CDs/AgNPs system by simultaneous collection of fluorescence and SRS signals. The sensing system is further used for H2O2-generation bioanalysis, and as a proof-of-concept, ratiometric assay of glucose and evaluation of glucose oxidase activity are performed successfully. This work provides a new perspective for sensing applications of plasmonic nanoparticles.

As one of critical base excision repair enzymes, uracil-DNA glycosylase (UDG) can specifically repair uracil-induced DNA damage to maintain the genome integrity of organisms. Moreover, abnormal expression of UDG is related to various cancers and other serious diseases. Therefore, it is essential to accurately and sensitively monitor UDG activity. In this work, a ratiometric fluorescence method using poly-(thymine) DNA template copper nanoclusters (Cu NCs) and 4′,6-diamidino-2-phenylindole (DAPI) as the output signals is developed for simple, selective, and sensitive detection of UDG. A double-stranded DNA (dsDNA) consisting of a uracil-containing single chain and a trigger sequence is designed as a substrate dsDNA. Meanwhile, another dsDNA comprising 30 pairs of A-T bases ((AT)30 dsDNA) is designed to be partially complementary to the trigger chain. The (AT)30 dsDNA itself has no blunt or recessed 3′ end and cannot be cut by exonuclease III (Exo III). With the Exo III-assisted amplification, adding UDG results in the success synthesis of red-emissive Cu NCs, while the dsDNAs in the system are hydrolyzed and the fluorescence signal of DAPI is weak. In contrast, without addition of UDG, the fluorescence intensity of Cu NCs is low, while the DAPI emits significantly enhanced fluorescence signal. The proposed method presents a detection limit of 5.0 × 10−5 U mL−1 and can be applied to the HeLa cell lysate sample with satisfactory results. Additionally, the kinetic parameter is studied and the UDG inhibition effect is evaluated. In summary, this work provides a potential platform for DNA repair enzyme-related analysis and clinical diagnosis.

In this work, a facile and label-free ratiometric sensor is constructed for selective determination of norepinephrine (NE) by coupling second-order scattering (SOS) and fluorescence, two different and independent optical signals. Herein, polyethyleneimine (PEI) dilute solution medium shows an intensive SOS signal without any fluorescence response. Interestingly, NE can be selectively induced by PEI to emit bright fluorescence, and meanwhile causes an observable decrease in the SOS signal due to the interactions between NE and PEI. The simultaneous variation of the two independent signals can be used for ratiometric sensing of NE. Under the optimal conditions, the resultant ratiometric sensor displays high sensitivity and selectivity toward NE by simultaneously monitoring fluorescence and SOS signals with the same excitation wavelength. The proposed sensor exhibits a good linear relationship versus NE concentration in the range of 10.0 nM-45.0 μM with a detection limit of 2.0 nM (S/N = 3) and has been successfully applied to the determination of NE in real samples without the use of any extra reagent. The combination of fluorescence and SOS signals provides a new scheme for ratiometric sensor design, greatly simplifying experimental procedure and effectively enhancing detection accuracy. Moreover, the proposed analytical strategy further broadens the application of dilute solutions of polymers in research into optical sensor and green analytical chemistry. Graphical abstract.

We present a facile method for the preparation of red-emitting and water-soluble silver nanoclusters (Ag NCs) using dihydrolipoic acid and sodium borohydride as the template and reducing agent. Ethanol solvent is demonstrated to endow Ag NCs with dramatically enhanced fluorescence; therefore, the Ag NCs are synthesized in ethanol/water solution (e/w-Ag NCs) instead of aqueous solution. Specific trivalent chromium (Cr3+) recognition capability of the e/w-Ag NCs can thus be obtained on the basis of its fluorescence quenching. The mechanisms for fluorescence enhancement and quenching of the e/w-Ag NCs triggered by ethanol and Cr3+, respectively, are investigated in detail. Next, a fluorescence method for detection of Cr3+ is established and its analytical performance is evaluated: the detection limit for Cr3+ is 0.71 μM and the linear range is from 2 to 40 μM. The fluorescent probe exhibits sufficient sensitivity and good selectivity toward Cr3+, illustrating that it has great promise for practical application in Cr3+ detection.

A simple and label-free fluorescence turn-on method is proposed for the discrimination and detection of epinephrine (Ep) and dopamine (DA) via polyethyleneimine (PEI)-initiated in situ copolymerization and excitation wavelength switch. The PEI solution in the presence of Ep, DA and the mixture of Ep and DA are denoted as PEp-PEI, PDA-PEI and MEp+DA, respectively. In this study, PEI aqueous solution medium initiates the auto-oxidization of Ep and DA and the bioinspired copolymerization. These resultant copolymers emit yellow-green fluorescence color with a fluorescence emission maximum at 515 nm. Interestingly, these fluorescent copolymers exhibit distinct different excitation spectra, although Ep and DA are structurally very similar. PDA-PEI exhibits only one excitation peak at 385 nm, and PEp-PEI shows dual-excitation mode with two significant excitation peaks at 328 nm and 405 nm, respectively. MEp+DA also shows dual-excitation mode with two excitation peaks at 330 nm and 395 nm, respectively. Thus, individual Ep, DA, and their mixture can be discriminated based on the different excitation spectral shapes and peak locations of PEp-PEI, PDA-PEI and MEp+DA. Furthermore, the quantitative analysis of Ep and DA in mixture can also be achieved by switching excitation wavelength between 330 and 395 nm and monitoring the fluorescence emission intensity of MEp+DA at 515 nm. The fluorescence intensity of MEp+DA only related to the concentration of Ep when excited at 330 nm. Moreover, the concentration of DA can also be calculated by subtracting the fluorescence intensity of PEp-PEI from the total fluorescence intensity when excited at 395 nm. The resultant method has been used to simultaneously detect Ep and DA in human urine samples. The proposed fluorescence system is facile, eco-friendly, low-cost, and time-saving, and also provides a new and simple path for discriminating analogues.

In this work, novel photoluminescent Ag nanoclusters (Ag NCs) with red emission are synthesized and successfully used for detecting iodide ion (I−). The dihydrolipoic acid (DHLA) is used as the stabilizing agent and beta-cyclodextrin (β-CD) is used as the auxiliary stabilizing agent. DHLA and β-CD are combined with Ag atoms by the formation of Ag S bonds and hydrophobic interaction, respectively. Functionalization of β-CD endows good photoluminescent properties and solubility in water to the Ag NCs. The obtained DHLA and β-CD-protected Ag NCs (DHLA/β-CD-Ag NCs) are spherical and display a dispersed state. However, the DHLA/β-CD-Ag NCs are aggregated in the presence of I−, accompanied by the decrease in their fluorescence intensity. Because the integrity of β-CD cavities is retained on the surface of DHLA/β-CD-Ag NCs, which preserves their capability for I− host–guest recognition, the DHLA/β-CD-Ag NCs combine with I− through the formation of inclusion complexes. Based on this phenomenon, the prepared DHLA/β-CD-Ag NCs can be designed as a novel fluorescent probe for I− detection. The limit of detection (LOD) is calculated as 0.06 μM, indicating that it is an ideal probe for I− detection in practical applications.

A simple ratiometric fluorescent and colorimetric dual-signal sensing system for Cu2+ and pyrophosphate ion (PPi) detection is established based on N-doped carbon dots (N-CDs) which are synthesized via one-step hydrothermal approach. In the strategy, 2,3-diaminophenazine (oxOPD), the oxidation product of o-phenylenediamine (OPD), can be adsorbed on the surface of N-CDs through electrostatic interaction, which efficiently quenches the fluorescence of N-CDs, meanwhile, oxOPD provides a new emission peak at 553 nm. In virtue of the selective oxidative and chromogenic reaction of OPD with Cu2+, a dual-readout sensing system for Cu2+ is achieved. In addition, the redox and chromogenic reaction among them can be inhibited by PPi, which protects effectively the fluorescence of N-CDs from quenching. This sensing system exhibits good selectivity and sensitivity toward Cu2+ and PPi over other analytes with a low detection limit of 23 nM and 0.7 μM, respectively. Furthermore, the proposed sensing system displays a prospective application for quantitative assay of Cu2+ and PPi in practical samples.

The development of ratiometric fluorescent strategy is very significant and challenging in bioanalysis. Herein, graphitic carbon nitride (g-C3N4) nanosheets and cobalt oxyhydroxide (CoOOH) nanoflakes are exploited for ratiometric fluorescence assay of alkaline phosphatase (ALP) activity. In the g-C3N4/CoOOH nanohybrid, g-C3N4 nanosheets serve as a signal unit and the CoOOH nanoflakes function as a recognition element, and initially, the fluorescence of g-C3N4 is quenched by the CoOOH nanoflakes. In the absence of target, the CoOOH nanoflakes of the nanohybrid system are able to oxidize o-phenylenediamine (OPD), and the resultant oxidation product (OxOPD) quenches the blue emission of g-C3N4 and meanwhile emits orange fluorescence which acts as another signal element. However, an efficient redox reaction between ascorbic acid (AA) and CoOOH can cause decomposition of the CoOOH nanoflakes, and additionally, ALP can catalytically hydrolyze L-ascorbic acid-2-phosphate (AAP) to generate AA. Thus, in the presence of target, the CoOOH nanoflakes are destroyed by AA preferentially and the OPD is rarely oxidized to OxOPD, accompanied with strong blue emission of g-C3N4 and weak orange fluorescence from OxOPD. Target-dependent dual-signal change made the ratiometric assay possible, and also AA-induced signal variation was investigated and attributed to the stronger reducing capacity of AA than OPD. The ratiometric sensing platform for ALP activity assay provides a new perspective for the applications of two-dimensional nanomaterials to develop novel and sensitive biosensors.

The Red-emitting nitrogen-doped carbon dots (N-CDs) are synthesized using o-phenylenediamine by a one-step method, and can serve as a fluorescent probe for "turn off" detection of hematin in human red cells. The red-emitting N-CDs can be obtained only in acidic conditions and the emission of the red-emitting N-CDs is pH-dependent, indicating proton-controlled synthesis and emission. The red-emitting N-CDs are 2.7 nm in mean size and have a uniform dispersion and exhibit a high quantum yield (12.8%) and great optical properties. The developed sensing system for hematin displays a linear response from 0.4 to 32 μM with a detection limit of 0.18 μM. Importantly, this fluorescent probe demonstrates a good potential practicability for the quantitative detection of hematin in complex matrixes. Graphical abstract ᅟ.

Intrinsic activity modifying of electrocatalysts is crucial to realizing the excellent catalytic performance towards hydrogen evolution reaction. Herein, we demonstrate a highly efficient electrocatalyst based on heterogeneous cobalt phosphides nanoparticles. The ultrafine size of the as-prepared catalyst (∼5 nm) ensures the efficient extension of active sites. Furthermore, the incorporation of orthorhombic CoP and Co2P contributes to the improvement of the inherent catalytic property. As a consequence, the as-prepared heterogeneous cobalt phosphides nanoparticles supported on carbon cloth exhibit impressive electrocatalytic activity, which only acquire a small overpotential of 90 mV at a current density of 10 mA cm−2, and present a low Tafel slope (67.9 mV dec−1), a large exchange current density (0.58 mA cm−2) as well as good durability. Therefore, this work provides a favorable guidance for exploring executable strategies to improve catalyst activity.

In this work, a two-dimensional optical sensing platform for H2O2, glucose, and uric acid (UA) detection is developed, which integrates the advantages of colorimetric and ratiometric fluorescent techniques. ZnFe2O4 magnetic microspheres with an intrinsic peroxidase-like activity are synthesized to catalyze the oxidation of o-phenylenediamine in the presence of H2O2, producing a typical yellow substance (oxOPD) with an absorption peak at 420 nm. The oxOPD can significantly quench the fluorescence of boron and nitrogen co-doped CDs (B,N-CDs) at 430 nm through the inner filter effect and generate a new fluorescence emission peak at 556 nm. Thus, the fluorescence intensity ratio (I556/I430) can be utilized for quantitative analysis of the concentrations of H2O2 and H2O2-involved metabolites (glucose and UA). The colorimetric “naked-eye” readout based on the color change of solution can also be established to determine H2O2, glucose, and UA levels. The detection limit based on colorimetric sensing for H2O2, glucose, and UA are 0.09, 0.9, and 0.9 μM, respectively, and 0.1, 8, and 1 μM using ratiometric fluorescent sensing. Furthermore, this strategy can detect glucose and UA in human serum with satisfactory results, and provide potential applications in the detection of metabolites related to H2O2 release.

Since uracil-DNA glycosylase (UDG) is closely related to some human diseases, monitoring and detection of UDG activity have great significance in its clinic diagnosis and functional study. Here we demonstrate a sensitive cascade multi-amplification fluorescence strategy for the active UDG assay with the help of exonuclease III (Exo III). Under the cleavage reaction of UDG, the double-stranded DNA containing peculiar uracil bases separated into two dissociative single-stranded DNA, which separately hybridized with two cyclic hairpin probes to launch the Exo III-assisted dual cycles. The hairpin DNA modified with fluorophore and quenching group was employed as the signal probe. After the dual cycles, countless same short DNA fragments were generated to hybridize with signal probes, initiating a new Exo III-assisted cyclic amplification and releasing numerous single-stranded DNA which carried only fluorophores. Thus, the fluorescence intensity of the detection system was enhanced. This study obtained the detection limit as low as 2.4 × 10−4 U/mL for detecting the UDG activity. And it performed satisfactory selectivity and well practical applicability by analysis of the HeLa cell lysate, providing a potential method for clinic diagnosis and functional study of UDG activity.

A fluorescence method for the determination of picric acid (PA) using phosphorus-doped carbon dots (P-CDs), synthesized from β-cyclodextrin and sodium pyrophosphate, is described. The P-CDs are very uniform and monodisperse with a diameter of about 2.8 nm. Under an excitation of 350 nm, the P-CDs emit bright blue fluorescence with an emission peak at 440 nm. The as-synthesized P-CDs serve as a sensitive, selective, and label-free fluorescent probe for the detection of PA. Based on an inner filter effect between PA and P-CDs, a linear response is obtained for PA from 0.1 to 10 μM with a detection limit of 82 nM. Finally, this sensing system has been demonstrated to have practicability for PA detection in the environmental water samples.

Water electrolysis is an important way to gain pure hydrogen, while it is restricted by the sluggish kinetics of oxygen evolution reaction. To improve hydrogen production capability, it is critical to search for low-cost, earth-abundant, and superior catalytic activity materials as electrocatalysts for water oxidation. Herein, one-step chemical transformation strategy is utilized to synthesize cobalt sulfide nanosheets supported on the carbon cloth through the sulfuration process of the Co3O4 precursor. The catalyst exposes abundant active sites and facilitates charge transfer, which is beneficial to water oxidation. In alkaline electrolyte, the catalyst as a non-noble metal electrode exhibits sparkly performance for water oxidation. To achieve current densities of 10 and 100 mA cm−2, the overpotentials as low as 291 and 364 mV are demanded, respectively. Moreover, cobalt sulfide nanosheets on the carbon cloth manifest a small Tafel slope of 69 mV dec−1 and robust long-term durability. In addition, this one-step chemical transformation strategy can be utilized to synthesize cobalt selenide nanosheets on the carbon cloth, providing an orientation for developing other binder-free electrocatalysts for water oxidation.

Due to rapid change in information technology, many consumer electronics become electronic waste which is the fastest-growing pollution problems worldwide. In fact, many discarded electronics with prefabricated micro/nanostructures may provide a good basis to fulfill special needs of other fields, such as tissue engineering, biosensors, and energy. Herein, to take waste optical discs as an example, we demonstrate that discarded electronics can be directly repurposed as highly anisotropic platforms for in vitro investigation of cell behaviors, such as cell adhesion, cell alignment, and cell-cell interactions. The PC12 cells cultured on biocompatible DVD polycarbonate layers with flat and grooved morphology show a distinct cell morphology, indicating the topographical cue of nanogrooves plays a key role in guidance of neurites growth. By further monitoring cell morphology and alignment of PC12 cells cultured on the DVD nanogrooves at different differentiation times, we find that cell contact interaction with nanotopographies is dynamically adjustable with differentiation time from initial disorder to final order. This study adds a new dimension to not only solving the problems of supply of materials and fabrication of nanopatterns in neural tissue engineering, but may also offering a new promising way of waste minimization or reuse for environmental protection.

Herein, we report a facile method to synthesize red-emitting, water-soluble Ag nanoclusters (Ag NCs) employing lipoic acid as a stabilizing agent. The Ag NCs show aggregation-induced emission property and have good stability and optical properties. Cu2+ can disperse the aggregated Ag NCs, accompanied by the quenching of fluorescence. However, the formed Cu2+-melamine complex by the coordination chemistry between free copper ion and melamine is able to effectively avoid the quenching process of Cu2+ to the Ag NCs. Hence, the Ag NCs can be applied to design a novel fluorescent probe based on this property to detect melamine. In the determination of melamine, the as-prepared fluorescent Ag NCs exhibit favorable sensitivity and high selectivity. The limit of detection (LOD) down to 0.022 mg/L and good recoveries of real sample experiments were obtained. This fluorescent probe is proved to be convenient and rapid for detecting melamine, with potential application to trace melamine analysis in complicated samples.

Selective and sensitive detection of multiple metal ions is significant for biological researches and environmental monitoring, because the abnormal metal ions levels have potential damage to the human body and environment. In this study, a fluorescent sensing platform based on Ag nanoclusters has been established for independent detection of Hg2+, Cu2+, and Fe3+ ions in a solution. The interference of the fluorescence induced by coexistent metal ions was removed by altering buffers with different pH and using different masking agents. Moreover, the detection mechanism is discussed in detail, which provides a valuable reference for the detection of heavy metal ions with metal nanomaterials. This sensor exhibits a high selectivity and sensitivity, and the linear ranges for Hg2+, Cu2+, and Fe3+ detection are 0.05-9, 0.05-18, and 0.1–18 μM with the corresponding detection limits of 12, 27, and 50 nM, respectively. Furthermore, this method was successfully used for analyzing the three metal ions in environmental and biological samples.

p-Nitrophenol (p-NP) contaminants seriously endanger environmental and living beings health, hence to establish a sensitive and selective method is of great importance for the determination of p-NP. In this work, boron and nitrogen co-doped carbon dots (B,N-CDs) were synthesized by one-step hydrothermal method using 3-aminophenylboronic acid as the sole precursor. The product was characterized through high-resolution transmission electron microscopy, fluorescence spectroscopy, UV–visible absorption spectroscopy, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy. Without any functionalized modification, B,N-CDs can be directly applied as a ‘turn-off’ fluorescent probe for rapid, highly selective, and sensitive detection of p-NP. The fluorescent sensor based on the B,N-CDs exhibited a broad linear response to the concentration of p-NP in the range of 0.5 − 60 μM and 60 − 200 μM, respectively, and provided a detection limit of 0.2 μM. It was found that only the absorption spectrum of p-NP has a wide overlap with the fluorescence excitation and emission spectra of B,N-CDs compared to those of other representative analogues. The response mechanism was due to the inner filter effect and the formation of dynamic covalent B-O bonds between B,N-CDs and p-NP, which endowed the sensing platform with the rapid response and high selectivity to p-NP. Finally, the sensor showed the practicability of p-NP determination in environmental water samples.

In order to detect ascorbic acid (AA) sensitively, a dual-signal optical sensor of a nanosystem with carbon dots (CDs)/MnO2 nanosheets based on fluorescence and second-order scattering (SOS) has been constructed. Here, MnO2 nanosheets, both as a fluorescence quencher and signal transducer of SOS, quench the blue fluorescence of CDs by an inner filter effect. Under the excitation of 300 nm, the nanosystem shows a fluorescence emission peak at 405 nm and a SOS peak at 610 nm, respectively. With the increase of AA , the lamellar structure of MnO2 nanosheets is etched into a smaller nanostructure, causing a decrease of the fluorescence recovery of CDs (405 nm) and decrease of the SOS signal of the MnO2 nanosheets (610 nm). According to the simultaneous changes of fluorescence and SOS signals, a dual-signal optical sensor toward AA is successfully constructed. Satisfactorily, the optical sensor for AA detection shows a detection limit of 88 and 105 nM for fluorescence and SOS, respectively. The practical application of the designed sensor is verified through the detection of AA content in vitamin C tablets, and satisfactory results are obtained

Herein, an innovative photocathodic enzymatic biosensor is proposed with poly {4,8-bis[5-(2-ethylhexyl)thiophen-2-yl]-benzo[1,2-b:4,5-b']dithiophene-2,6-diyl-alt-3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophene-4,6-diyl} (PTB7–Th) as donor–acceptor–type photoactive material and three–dimensional (3D) polyaniline hydrogels (PAniHs) as both electron transfer layer and biomolecule carrier. Based on the enhancement effect of PAniHs on the charge separation and electron transfer of PTB7–Th and the competitive consumption of dissolved oxygen (O2) between the xanthine oxidase (XOD)–guanine catalytic reaction and O2–sensitive PTB7–Th/PAniHs, the proposed photocathodic enzymatic biosensor has been demonstrated to detect guanine with the advantages of low limit of detection (0.02 μM), wide linear range (from 0.1 to 80 μM), simple and convenient preparation process, satisfactory stability, and photochemical signal amplification independent of any exogenous electron donor/acceptor or sensitizer. Remarkably, the proposed photocathodic enzymatic biosensor can not only be extended to other aerobic enzymatic bioanalyses, but also pave a horizon for the application of environmentally friendly conductive hydrogel materials in photoelectrochemical bioanalysis.

Designing low-cost and high-active bifunctional catalysts for overall water splitting has attracted increasing research interest. Herein, the brilliant overall water splitting performance of cobalt-vanadium bimetal-based nanocomposites is explored. Co-V based nanocomposites are synthesized through a one-step hydrothermal method, in which the cobalt species is introduced into the lepidocrocite VOOH and further cobalt vanadium oxide is formed. The additive level of cobalt is optimized and the corresponding effect on electrocatalytic activity is also investigated in this work, systematically. The targeted catalyst (denoted as Co0.2-VOOH) exhibits a unique sheet-like morphology, resulting in the high exposure of catalytically active sites. When used as the bifunctional catalyst, Co0.2-VOOH can achieve a current density of 10 mA cm-2 at the overpotentials of 210 mV for water oxidation and 130 mV for hydrogen generation, respectively. Notably, it only requires low cell voltages of 1.57 and 1.74 V to drive the catalytic current densities of 10 and 100 mA cm-2 during the water splitting process. This work significantly indicates that cobalt-vanadium based materials are promising alternatives for overall water splitting.

Recently, metal organic frameworks (MOFs) have received intensive research interest as an important family of functional materials. In particular, MOFs were widely used in electroanalysis and water splitting for their electrical conductivity and rich redox electrochemical activities. Prussian blue analogue (PBA), which owns hollow nanostructured MOFs with large surface area and unique structural features, offers great advantages for constructing advanced electrodes. Meanwhile, compared with platinum-based catalysts, molybdenum disulfide (MoS2) is increasingly becoming a research focus as an affordable alternative obtaining electrochemical hydrogen production from water. Here we synthesized the nanomaterials, MoS2-Co nanoboxes, using the facile hydrothermal method between cobalt Prussian blue analogue (Co PBA) nanocubes and ammonium thiomolybdate ((NH4)2MoS4). In acid and alkaline media, the MoS2-Co nanoboxes exhibit favorable catalytic performance for the hydrogen evolution reaction (HER). Furthermore, for researching the relationship of structural changes of MoS2 supported on Co PBA nanocubes and HER catalytic performance, we use the Raman spectroscopy to monitor nanostructured MoS2 which can promote the exposure of the most active sites. This new method applied in this study can be widely adopted for characterization of transition metal dichalcogenides with various compositions for a wide range of applications.

Various experimental conditions were tested for the green extract process of corrosion inhibitor from lychee fruit waste, and the optimal extract parameters were selected using potentiodynamic polarization. The best inhibition effect of the ethanol extract of lychee’s peel and seed by ultrasound for 1.5 h (EELPS) for mild steel in 0.5 M HCl was obtained at 600 mg/L using electrochemical and weight loss measurements. Theoretical calculations illustrate the adsorption sites and adsorption behavior of effective compounds. Due to the existence of hydroxyl groups and phenol rings in the main components, EELPS is considered to be a good inhibitor.

Gold nanomaterials (AuNMs)-based “naked-eye” sensing strategies are highly attractive due to their straightforward operations, valid mechanisms, and rapid processes. The strategies are mainly developed by exploiting the distinct properties of AuNMs, including localized surface plasmon resonance, and catalytic activity. The presence of target alters the inherent AuNMs’ properties, resulting with the sample color change that could be readily observed with naked eyes. Significantly, these visualization sensing platforms could be further expanded by incorporating technologies like enzyme reactions, metal ions-specific attachment, DNA hybridization, and even immunoassay. Herein, we describe the fundamental preparation strategies of AuNMs to yield their unique structures and tunable properties. Subsequently, AuNMs-based sensing strategies of which have shown sensitive and selective analytical sensing of different targets are discussed. We would further impart our insights and ideas following our analysis of current strategies in AuNMs-based visual sensing. This, we hope, would inspire more advanced nanomaterials-based visual sensors development.

The various synthetic routes of carbon dots (C-dots) feature a considerable step toward their potential use in sensors and biotechnology. Herein, by coupling pyrophosphate introduction with high-energy phosphate bond design, the fluorescence performance of C-dots is improved greatly. The introduction of pyrophosphate acts as the nucleus growth-inhibitor to protect C-dots from assembling and growing into large carbon particles. The high-energy phosphate bond is designed as an energy-donor to provide energy for synthesizing C-dots. The C-dots exhibit enhanced fluorescence with a high quantum yield of 24.8%. Then the C-dots are employed as the fluorescent probe to develop hydrogen peroxide (H2O2)-related biosensors. The mechanism is based on the fluorescence quenching of C-dots caused by the highly reactive OH and Fe3+ during the Fenton reaction. A wide linear range (0.5–100 μM) and a low detection limit (0.195 μM) are achieved for H2O2 detection. Moreover, the probe can be applied to H2O2-related biosensing in the presence of oxidase. As a proof-of-concept, a glucose sensor is developed with glucose oxidase. The presented glucose sensor exhibits good selectivity and high sensitivity with a detection limit of 0.254 μM. Additionally, the practical application of the proposed biosensor has been confirmed by detecting glucose in human serum samples.

Patterning graphene allows to precisely tune its properties to manufacture flexible functional materials or miniaturized devices for electronic and biomedical applications. However, conventional lithographic techniques are cumbersome for scalable production of time- and cost-effective graphene patterns, thus greatly impeding their practical applications. Here, we present a simple scalable fabrication of wafer-scale three-dimensional (3D) graphene micropatterns by direct laser tuning graphene oxide reduction and expansion using a LightScribe DVD writer. This one-step laser-scribing process can produce custom-made 3D graphene patterns on the surface of a disk with dimensions ranging from microscale up to decimeter scale in about 20 min. Through control over laser-scribing parameters, the resulting various 3D graphene patterns are exploited as scaffolds for controlling cell alignment. The 3D graphene patterns demonstrate their potential to biomedical applications, beyond the fields of electronics and photonics, which will allow to incorporate flexible graphene patterns for 3D cell or tissue culture to promote tissue engineering and drug testing applications.

Glutathione (GSH), as a crucial endogenous thiol and antioxidant, plays an essential role in the biological system, and its abnormal levels are closely related to various diseases. Therefore, it continues to be of enormous significance to develop a sensitive and efficient method for the assay of GSH. Herein, we report a facile and sensitive polymer dots (PDs)-manganese dioxide (MnO2) nanosensor for turn-on assay of GSH. In this sensing system, the PDs with strongly green fluorescence were prepared by a mild one-step method using hydroquinone and ethylenediamine as precursors, and the fluorescence of PDs can be quenched by MnO2 nanosheets. The PDs-MnO2 nanosensor was the turn-off state. In the presence of GSH, however, the fluorescence of the PDs-MnO2 nanosensor can remarkably recover because MnO2 nanosheets can be reduced into Mn2+ by GSH. The PDs-MnO2 nanosensor was the turn-on state. Based on the change of the fluorescence signal from turn-off switched to turn-on, a sensitive method was successfully constructed to detect GSH. We also systematically discussed the mechanism of the PDs-MnO2 nanosensor for GSH assay, indicating that the MnO2 nanosheets-induced the fluorescence quenching was derived from inner filter effect (IFE). The PDs-MnO2 nanosensor toward GSH showed a wide linear range from 0.5 to 200 μM and high sensitivity with a limit of detection of 0.10 μM. The as-developed PDs-MnO2 nanosensor was also successfully applied to detect GSH in human serum with satisfactory results.

A novel water-soluble fluorescent polydopamine derivative, polydopamine-glutathione nanoparticles (PDA-G (-S-)NPs), was synthesized by the Michael addition reaction between dopamine (DA) and reduced glutathione (GSH). Compared to a direct polymerization of dopamine, the as-prepared PDA-G (-S-)NPs have stronger fluorescence emission intensity. Also, the synthesis does not need any hazardous organic solvents and the process is simple. Additionally, the roles of GSH and hydrogen peroxide (H2O2) in enhancing the fluorescence intensity are discussed in detail. The thioether in PDA-G (-S-)NPs is easily oxidized by hydrogen peroxide to sulfoxide and sulfone groups, accompanied by a decrease in fluorescence intensity. Therefore, the PDA-G (-S-)NPs can be applied to construct a fluorescent sensor for the sensitive detection of hydrogen peroxide. Based on the transformation of glucose into gluconic acid and H2O2 in the presence of glucose oxidase, the PDA-G (-S-)NPs system was further utilized to sensing glucose. The linear ranges and detection limits of hydrogen peroxide and glucose are (0.5–6 μM, 2–130 μM) and (0.15 μM, 0.6 μM), respectively.

Unique water-soluble endogenous fluorescent polydopamine-glutathione nanoparticles (PDA-GNPs) with high fluorescence quantum yield were firstly prepared through Michael addition reaction of glutathione and polydopamine. The PDA-GNPs were prepared under mild conditions, and the preparation process was facile (one-pot reaction) and environmentally friendly. With the introduction of Fe 3+ , the fluorescence intensity of PDA-GNPs decreased sharply. Interestingly, the fluorescence can restore by adding PPi to the system of PDA-GNPs/Fe 3+ . Based on these phenomena, a probe for quantification of Fe 3+ and PPi was set up. With a wide linear range of 0.1–300 μM, the probe can be used to determine Fe 3+ in practical water samples because of its nanomolar magnitude detection limit and negligible influences of other interferences. As to the detection of PPi, the linear range was 2–12 μM and the detection limit was 0.6 μM. In addition, an IMPLICATION logic gate was built by utilizing Fe 3+ and PPi as inputs and the fluorescence signal of PDA-GNPs as output.

As one of the DNA damage repair enzymes, uracil-DNA glycosylase (UDG) plays an important role in maintaining genomic integrity. By linked bridge hybridizing-induced split G-quadruplex (SQ), we demonstrate here the construction of a simple and sensitive DNA machine for the detection of UDG activity. The satisfactory split G-quadruplex sequences (SQS) were successfully selected to be the ingredients of SQ formation. In this work, UDG recognized and removed the uracil bases from the stem of hairpin DNA (HP). And then, HP with a low melting temperature hybridized with designed SQS, forming a three-way DNA structure with an SQ. With the addition of Thioflavin T, a dramatical enhancement of fluorescence intensity was presented due to the G-quadruplex/Thioflavin T complex formation. The detection limit was as low as 7.8 × 10−3 U/mL. And we also successfully investigated the performance of UDG activity in the HeLa cell lysate. This optical DNA machine with the merits of being simple, rapid, and economical was flexibly suitable for not only active UDG assay but also diverse target detection by adjusting the recognition region of the HP.

The detection of disease-related DNA is of great significance for early and accurate diagnosis and therapy. In this work, we successfully achieved the sensitive detection of target DNA based on a thioflavin T (ThT)-induced G-quadruplex fluorescent biosensor. ThT, a water-soluble fluorescent dye, can induce G-rich sequences to form G-quadruplexes and obtain an obviously enhanced fluorescence. In this work, it was employed to construct a biosensor for the detection of HIV. When the target HIV existed, the hairpin DNA probes would be opened in succession and release the completely exposed G-rich sequence to combine with ThT. The simple and rapid biosensor performed satisfactory selectivity; it also exhibited sensitivity with a detection limit of 2.4 nM. With good performance in human serum, we believe that this optical biosensor has the potential to be applied to the practical detection of target DNA.

Lowering the dimension of transition metal dichalcogenides is an efficient approach to expose more S-edge-sites. Here, zero-dimensional MoS2 and WS2 nanodots are successfully prepared with the assistance of a template of NiNi Prussian blue analogue nanoplates. The novel hybrids exhibit highly efficient and stable catalytic ability for the hydrogen evolution reaction.