Electrophoretic Microplate Protein Identification Based on Gold Staining of Molybdenum Disulfide Hydrogels.

Numerous high-performance nanotechnologies have been developed, but their practical applications are largely restricted by the nanomaterials' low stabilities and high operation complexity in aqueous substrates. Herein, we develop a simple and high-reliability hydrogel-based nanotechnology based on the in situ formation of Au nanoparticles in molybdenum disulfide (MoS2)-doped agarose (MoS2/AG) hydrogels for electrophoresis-integrated microplate protein recognition. After the incubation of MoS2/AG hydrogels in HAuCl4 solutions, MoS2 nanosheets spontaneously reduce Au ions, and the hydrogels are remarkably stained with the color of as-synthetic plasmonic Au hybrid nanomaterials (Au staining). Proteins can precisely mediate the morphologies and optical properties of Au/MoS2 heterostructures in the hydrogels. Consequently, Au staining-based protein recognition is exhibited, and hydrogels ensure the comparable stabilities and sensitivities of protein analysis. In comparison to the fluorescence imaging and dye staining, enhanced sensitivity and recognition performances of proteins are implemented by Au staining. In Au staining, exfoliated MoS2 semiconductors directly guide the oriented growth of plasmonic Au nanostructures in the presence of formaldehyde, showing environment-friendly features. The Au-stained hydrogels merge the synthesis and recognition applications of plasmonic Au nanomaterials. Significantly, the one-step incubation of the electrophoretic hydrogels leads to high simplicity of operation, largely challenging those multiple-step Ag staining routes which were performed with high complexity and formaldehyde toxicity. Due to its toxic-free, simple, and sensitive merits, the Au staining integrated with electrophoresis-based separation and microplate-based high-throughput measurements exhibits highly promising and improved practicality of those developing nanotechnologies and largely facilitates in-depth understanding of biological information.

Tailoring Efficient Fluorogenic Tactic for Ultrasensitive Detection of Dopamine in Urine and Rat Brain through Real-Time and In Situ Formation of High-Performance Fluorophore.

Owing to the predominance of dopamine (DA) in controlling mental health, planning an innovative method for DA detection with simplicity and high efficacy is conducive to the assessment of neurological disorders. Herein, an efficient fluorogenic tactic has been elaborated for ultrasensitive detection of DA with remarkably enhanced turn-on response. Utilizing a twisted intramolecular charge-transfer (TICT)-suppressing strategy, a highly emissive azocine derivative 11-hydroxy-2,3,6,7,11,12,13,14-octahydro-1H,5H,10H-11,14a-methanoazocino[5',4':4,5]furo[2,3-f]pyrido[3,2,1-ij]quinolin-10-one (J-Aza) is generated via a one-step reaction between DA and 8-hydroxyjulolidine. It is marvelous that J-Aza not only possesses ideal fluorescence quantum yield (ΦF) as high as 0.956 but also exhibits bathochromic shifted fluorescence (green emissive) and stronger anti-photobleaching capacity superior to traditional azocine-derived 1,2,3,4-tetrahydro-5H-4,11a-methanobenzofuro[2,3-d]azocin-5-one (Aza) with moderate ΦF, blue fluorescence, and poor photostability. By confining the TICT process, the detection limit to DA can be reduced to 80 pM, which is competitive in contrast to previously reported fluorescence methods. Encouraged by the instant response (within 90 s), wide linear range (0.1-500 nM), great selectivity, and excellent sensitivity, this fluorogenic method has been used for the real-time measurement of DA contents in practical urine samples with satisfactory results. Furthermore, the cerebral DA level in the reserpine-induced depression rat model has also been evaluated by our designed method, demonstrating its potent analytical applicability in the biosensing field.

Mercury-Mediated Epitaxial Accumulation of Au Atoms for Stained Hydrogel-Improved On-Site Mercury Monitoring.

Trivalent Au ions are easily reduced to be zerovalent atoms by coexisting reductant reagents, resulting in the subsequent accumulation of Au atoms and formation of plasmonic nanostructures. In the absence of stabilizers or presence of weak stabilizers, aggregative growth of Au nanoparticles (NPs) always occurs, and unregular multidimensional Au materials are consequently constructed. Herein, the addition of nanomole-level mercury ions can efficiently prevent the epitaxial accumulation of Au atoms, and separated Au NPs with mediated morphologies and superior plasmonic characteristics are obtained. Experimental results and theoretical simulation demonstrate the Hg-concentration-reliant formation of plasmonic nanostructures with their mediated sizes and shapes in the presence of weak reductants. Moreover, the sensitive plasmonic responses of reaction systems exhibit selectivity comparable to that of Hg species. As a concept of proof, polymeric carbon dots (CDs) were used as the initial reductant, and the reactions between trivalent Au and CDs were studies. Significantly, Hg atoms prevent the epitaxial accumulation of Au atoms, and plasmonic NPs with decreased sizes were in situ synthesized, corresponding to varied surface plasmonic resonance absorption performance of the CD-induced hybrids. Moreover, with the integration of sensing substrates of CD-doped hydrogels, superior response stabilities, analysis selectivity, and sensitivity of Hg2+ ions were achieved on the basis of the mercury-mediated in situ chemical reactions between trivalent Au ions and reductant CDs. Consequently, a high-performance sensing strategy with the use of Au NP-staining hydrogels (nanostaining hydrogels) was exhibited. In addition to Hg sensing, the nanostaining hydrogels facilitated by doping of emerging materials and advanced chem/biostrategies can be developed as high-performance on-site monitoring routes to various pollutant species.

Tracking the Growth of Chiral Plasmonic Nanocrystals at Molybdenum Disulfide Heterostructural Interfaces.

The way of accurately regulating the growth of chiral plasmonics is of great importance for exploring the chirality information and improving its potential values. Herein, cysteine enantiomers modulate the anisotropic and epitaxial growth of gold nanoplasmonics on seeds of exfoliated MoS2 nanosheets. The heterostructural Au and MoS2 hybrids induced by enantiomeric cysteine are presented with chiroptical characteristics, dendritic morphologies, and plasmonic performances. Moreover, the synthesis, condition optimization, formation mechanism, and plasmonic properties of Au and MoS2 dendritic nanostructures are studied. The chirality characteristics are identified using the circular dichroism spectra and scanning electron microscopy. Time-resolved transmission electron microscopy and UV-vis spectra of the intermediate products captured are analyzed to confirm the formation mechanism of dendritic plasmonic nanostructures at heterostructural surfaces. The specific dendritic morphologies originate from the synergistic impacts of heterostructural MoS2 interfaces and enantiomeric cysteine-induced anisotropic manipulation. Significantly, the developed synthesis strategy of chiral nanostructures at heterostructural interfaces is highly promising in promoting the understanding of the plasmonic function and crucial chirality bioinformation.

Engineered Superhydrophilic/Superaerophobic Catalyst: Two-Dimensional Co(OH)2-CeO2 Nanosheets Supported on Three-Dimensional Co Dendrites for Overall Water Splitting.

Efficient electrocatalysts require not only a tunable electronic structure but also great active site accessibility and favorable mass transfer. Here, a two-dimensional/three-dimensional (2D/3D) hierarchical electrocatalyst consisting of Co(OH)2-CeO2 nanosheet-decorated Co dendrites is proposed, named as Co(OH)2-CeO2/Co. Based on the strong electronic interaction of the Co(OH)2-CeO2 heterojunction, the electronic structure of the Co site is optimized, which facilitates the adsorption of intermediates and the dissociation of H2O. Moreover, the open 2D/3D structure formed by introducing the Co substrate further reduces the accumulation of heterogeneous nanosheets and promotes the radial diffusion of the electrolyte, significantly improving the utilization of active sites and shortening the electron transfer pathway. In addition, the superhydrophilic/superaerophobic interface achieved by constructing the hierarchical micro-nanostructure is beneficial to electrolyte infiltration and bubble desorption, thus ensuring favorable mass transfer. Therefore, Co(OH)2-CeO2/Co exhibits an excellent overall water-splitting activity in alkaline solution.

A wide-range ratiometric sensor mediating fluorescence and scattering based on carbon dots/metal-organic framework composites for the detection of bisulfite/sulfite in sugar.

Bisulfite (HSO3-) and sulfite (SO32-) are commonly employed in food preservatives and are also significant environmental pollutants. Thus, developing an effective method for detecting HSO3-/SO32- is crucial for food safety and environment monitoring. In this work, based on carbon dots (CDs) and zeolitic imidazolate framework-90 (ZIF-90), a composite probe (named CDs@ZIF-90) is constructed. The fluorescence signal and the second-order scattering signal of CDs@ZIF-90 are employed to ratiometricly detect HSO3-/SO32-. This proposed strategy exhibits a broad linear range for HSO3-/SO32- determination (10 µM to 8.5 mM) with a limit of detection of 2.74 µM. This strategy is successfully applied for evaluating HSO3-/SO32- in sugar with satisfactory recoveries. Therefore, this work has uniquely combined the fluorescence and second-order scattering signals to establish a novel sensing system with a wide linear range, which is applicable for ratiometric sensing of HSO3-/SO32- in actual samples.

Plasmonic Gold Nanoparticles Stain Hydrogels for the Portable and High-Throughput Monitoring of Mercury Ions.

The hybrid of l-cysteine and agarose can reduce HAuCl4 and support the rapid growth of plasmonic gold nanoparticles (Au NPs) in the hydrogel phase. The l-cysteine-doped agarose hydrogel (C-AGH) not only offers the substrate the capacity to reduce Au(III) ions but also stabilizes and precisely modulates the in situ grown Au NPs with high repeatability, easy operation, and anti-interference performance. Herein, before the incubation of HAuCl4, the improved hydrogel is preincubated in the aqueous solution containing mercury ions, and the cysteine can specifically conjugate with mercury via the thiol groups. Subsequently, the responsive allochroic bands from dark blue to red can be identified in the solid hydrogel after the incubation of HAuCl4, which is attributed to the formation of regulated Au-Hg nanoamalgams. As a proof-of-concept, toxic Hg2+ ions are exploited as targets for constructing novel sensing assays based on the improved C-AGH protocol. Based on naked-eye recognition, Hg2+ could be rapidly and simply measured. Additionally, the high-throughput and trace analysis with a low limit of detection (3.7 nM) is performed using a microplate reader. On the basis of the filtering technique and remodeling of hydrogels, C-AGH working as the filtering membrane can even achieve the integration of enrichment and measurement with enhanced sensitivity. Significantly, the strategy of using an allochroic hydrogel with the staining of Au NPs can promote the rapid and primary assessment of water quality in environmental analysis.

Universal and Programmable Rolling Circle Amplification-CRISPR/Cas12a-Mediated Immobilization-Free Electrochemical Biosensor.

The development of a sensing platform with high sensitivity and specificity, especially programmability and universal applicability, for the detection of clinically relevant molecules is highly valuable for disease monitoring and confirmation but remains a challenge. Here, for the first time, we introduce the clustered regularly interspaced short palindromic repeats (CRISPR)/Cas system into an immobilization-free electrochemical biosensing platform for sensitively and specifically detecting the disease-related nucleic acids and small molecules. In this strategy, a modular rolling circle amplification (RCA) is designed to transform and amplify the target recognition event into the universal trigger DNA strand that is used as the trigger to activate the deoxyribonuclease activity of CRISPR/Cas12a for further signal amplification. The cleavage of the target-activated blocker probe allows the methylene blue-labeled reporter probes to be captured by the reduced graphene oxide-modified electrode, leading to an obviously increased electrochemical signal. We only need to simply tune the sequence for target recognition in RCA components, and this strategy can be flexibly applied to the highly sensitive and specific detection of microRNAs, Parvovirus B19 DNA, and adenosine-5'-triphosphate and the calculated limit of detection is 0.83 aM, 0.52 aM, and 0.46 pM, respectively. In addition, we construct DNA logic circuits (YES, NOT, OR, AND) of DNA inputs to experimentally demonstrate the modularity and programmability of the stimuli-responsive RCA-CRISPR/Cas12a system. This work broadens the application of the CRISPR/Cas12a system to the immobilization-free electrochemical biosensing platform and provides a new thinking for developing a robust tool for clinical diagnosis.

Conversion of Fluorescence Signals into Optical Fingerprints Realizing High-Throughput Discrimination of Anionic Sulfonate Surfactants with Similar Structure Based on a Statistical Strategy and Luminescent Metal-Organic Frameworks.

To date, the effective discrimination of anionic sulfonate surfactants with tiny differences in structure, considered as environmentally noxious xenobiotics, is still a challenge for traditional analytical techniques. Fortunately, a sensor array becomes the best choice for recognizing targets with similar structures or physical/chemical properties by virtue of principal component analysis (PCA, a statistical technique). Herein, because of the beneficial construction of the statistical strategy and use of two types of luminescent metal-organic frameworks (LMOFs, NH2-UiO-66 and NH2-MIL-88) as sensing elements, high-throughput discrimination and detection of five anionic sulfonate surfactants and their mixtures are nicely realized for the first time. Significantly, the stacking interaction of aromatic rings and dynamic quenching play essential roles in the generation of diverse fluorescence responses and unique fingerprint maps for individual anionic sulfonate surfactants. Moreover, the mixtures of anionic sulfonate surfactants are also satisfactorily distinguished in environmental water samples, demonstrating the practicability of the sensor array. On the basis of the PCA method, this strategy converts general fluorescence signals into unique optical fingerprints of individual analytes, providing a new opportunity for the application of LMOFs in the field of analytes recognition.

Aggregation-induced responses (AIR) of 2D-derived layered nanostructures enable emerging colorimetric and fluorescence sensors.

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.

Multifunctional Binding Strategy on Nonconjugated Polymer Nanoparticles for Ratiometric Detection and Effective Removal of Mercury Ions.

Developing a multifunctional platform for the selective detection and effective removal of toxic ions is a major challenge when addressing heavy metal contamination in environmental science. Herein, novel nonconjugated polymer nanoparticles (PNPs) called mercaptosuccinic acid-thiosemicarbazide PNPs (MT-PNPs) with appealing fluorescence and stability are synthesized via facile one-step hydrothermal treatment for attractive sensing and simultaneous removal of mercury(II). Interestingly, aggregation-induced fluorescence switch-off and scattering enhancement are found upon the addition of Hg2+, rendering MT-PNPs as a ratiometric sensor for selective and accurate Hg2+ monitoring. A wide linear range (0.1-1471 µM) and a low detection limit (95 nM) are obtained. This dual-signal opposite responses triggered by Hg2+ originate from the formation of MT-PNP-Hg2+ congeries via the multisite binding between S,N,O-containing groups of MT-PNPs and mercury. Meanwhile, target-induced aggregation renders an effective Hg2+ separation from contaminative aqueous media by MT-PNPs, which exhibits a satisfactory absorption efficiency of 90.42% within 50 min. Upon the simple Na2S treatment, the MT-PNPs can be regenerated and reused. This work thus delivers an applicable method for the ratiometric detection and effective removal of mercury with the novel nonconjugated PNPs, offering potential in tackling the problem of heavy metal ion pollution for environmental monitoring and remediation.

Ratiometric assay of mercury ion based on nitrogen-doped carbon dots with two different optical signals: second-order scattering and fluorescence.

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. Graphical abstract.

Signal-off photoelectrochemical determination of miRNA-21 using aptamer-modified In2O3@Cu2MoS4 nanocomposite.

In2O3@Cu2MoS4 nanocomposite with superior photoelectrochemical (PEC) performance is used for the first time as a photoactivity material, and a signal-off PEC biosensing platform for miRNA detection has been successfully constructed. Firstly, the Cu2MoS4 nanosheets are synthesized by a hydrothermal method, and then, the homogeneous In2O3 nanoparticles (In2O3 NPs) are synthesized by calcination in the air. The In2O3@Cu2MoS4 nanocomposite is constructed with the Cu2MoS4 nanosheets as matrix and In2O3 NPs as sensitizer through a layer-by-layer assembly strategy. The nanocomposite with a tight interface and the matched band structure restrains the electron-hole pair recombination. Under visible light (400-700 nm), the nanocomposite exhibits a strong initial signal. With the catalyzed hairpin assembly, dozens of PbS quantum dots (QDs) are introduced on the surface of an electrode, significantly reducing the photocurrent of n-type In2O3@Cu2MoS4. Since PbS QDs can compete with the nanocomposite for light energy and electron donors, the signal decreased. Under optimal conditions, the biosensor manifests a broad linear range (1 fM-1 nM) and a low detection limit of about 0.57 fM, at a working potential of 0 V (vs. Ag/AgCl). The recovery of spiked human serum is between 94.0 and 102%, and the relative standard deviation (RSD) is between 1.3 and 2.7%. Therefore, the as-fabricated biosensor exhibits a potential for the determination of miRNA-21 in practical applications.Graphical abstract The In2O3@Cu2MoS4 nanocomposite owns a strong anode photocurrent signal, which can be used as a photoactive material to construct a "signal-off" biosensor for the detection of miRNA in non-enzymatically catalyzed hairpin assembly (CHA) reaction.

Redox induced dual-signal optical sensor of carbon dots/MnO2 nanosheets based on fluorescence and second-order scattering for the detection of ascorbic acid.

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 Graphical Abstract A dual-signal sensor of fluorescence (FL) and second-order scattering (SOS) based on the carbon dot (CD) and MnO2 nanosheet system for ascorbic acid (AA) detection is constructed, in which CDs are used for the FL mode and MnO2 nanosheets are used for the SOS mode.

Metal-Organic Framework as a Chemosensor Based on Luminescence Properties for Monitoring Cetyltrimethylammonium Bromide and Its Application in Smartphones.

Rapid and sensitive detection of surfactants has attracted more and more attention since surfactants not only cause water pollution but also affect the health of human beings. Luminescent metal-organic frameworks combining unique optical property and inherent permanent porosity for guest-host encapsulation are widely used in fluorescence detection. Here we report a ratiometric fluorescent probe (denoted as UiO-66-NH2@PB) based on a Zr-based metal-organic framework (UiO-66-NH2) and a fluorescent dye, phloxine B (PB), for visual and fluorescent determination of cationic surfactants (cetyltrimethylammonium bromide; CTAB). The intensity ratio of dual-emission sensor exhibits a linear response to the CTAB concentrations of 0.1-17 µM and obtains a low detection limit (0.074 µM). Moreover, this method has been successfully utilized to monitor CTAB in the environmental water samples with satisfied recoveries. Importantly, this work provides a new insight into developing smartphone-based sensor to realize a rapid, on-site visual and quantification-based detection of CTAB.

Enhanced photoelectrochemical sensing based on novel synthesized Bi2S3@Bi2O3 nanosheet heterostructure for ultrasensitive determination of L-cysteine.

The design of a low-cost and highly efficient photoactive heterojunction material for sensing is still a challenging issue. On the basis of the formation of sheet-like Bi2O3 via coating Bi2S3, a novel Bi2O3@Bi2S3 heterostructure is controllably synthesized via a facile water bath approach. The prepared Bi2O3@Bi2S3 nanosheets show a superior photoelectrochemical (PEC) performance for the detection of L-cysteine (L-Cys), and the photocurrent signal is three and four times higher than those of Bi2S3 and Bi2O3 under visible irradiation, respectively. Also, the heterostructure presents an outstanding linear range for the detection of L-Cys: 0.1-10,000 µM. In addition, the mechanism of improved PEC response of Bi2O3@Bi2S3 nanosheets is investigated according to the estimated energy band positions. Thus, the integration of the novel heterostructure and the photoelectrochemical technique demonstrates a rapid photocurrent response, showing a great effect on the performance of the sensing system and a new PEC method for highly selective and sensitive chemical detection. Graphical abstract.

Fabrication of silver nanoclusters with enhanced fluorescence triggered by ethanol solvent: a selective fluorescent probe for Cr3+ detection.

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 facile and label-free ratiometric optical sensor for selective detection of norepinephrine by combining second-order scattering and fluorescence signals.

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.

Proton-controlled synthesis of red-emitting carbon dots and application for hematin detection in human erythrocytes.

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.

Fluorometric and resonance Rayleigh scattering dual-mode bioprobe for determination of the activity of alkaline phosphatase based on the use of CoOOH nanoflakes and cobalt(II)-dependent DNAzyme-assisted amplification.

The authors describe a fluorometric and resonance Rayleigh scattering dual-mode scheme for detection of the activity and inhibition of alkaline phosphatase (ALP). The method utilizes (a) CoOOH nanoflakes, which have high resonance Rayleigh scattering activity and can strongly adsorb ssDNA, and (b) Co(II)-dependent DNAzyme assisted signal amplification. ALP specifically catalyzes the hydrolysis of ascorbic acid-2-phosphate to produce ascorbic acid which reduces CoOOH nanoflakes to Co(II) ion. The Co(II)-dependent DNAzyme is then activated by Co(II) ion, and this results in the cleavage of a substrate labeled with both a fluorophore and a quencher. Following hydrolysis, fluorophore and quencher become separated and the fluorescence measured at excitation/emission wavelengths of 490/518 nm recovers, while the RRS signal at 405 nm decreases. The method works on the 0.2 to 2000 U L-1 ALP activity range, and the detection limit is 0.05 U L-1. The method was used to validate the mechanism of the action of two classical ALP inhibitors (EDTA and Na3VO4). Conceivably, it can also be applied to screen for ALP inhibitors. Graphical abstract A bioprobe composed of cobalt oxyhydroxide (CoOOH) nanoflakes as the substrate and carrier, and Co2+-dependent DNAzyme containing guanine ribonucleotide (rG) and uracil ribonucleotide (rU) for circularly signal amplification is used for fluorometric determination of alkaline phosphatase (ALP) activity.