Enzymatic Galvanic Redox Potentiometry for In Vivo Biosensing.

Redox potentiometry has emerged as a new platform for in vivo sensing, with improved neuronal compatibility and strong tolerance against sensitivity variation caused by protein fouling. Although enzymes show great possibilities in the fabrication of selective redox potentiometry, the fabrication of an enzyme electrode to output open-circuit voltage (EOC) with fast response remains challenging. Herein, we report a concept of novel enzymatic galvanic redox potentiometry (GRP) with improved time response coupling the merits of the high selectivity of enzyme electrodes with the excellent biocompatibility and reliability of GRP sensors. With a glucose biosensor as an illustration, we use flavin adenine dinucleotide-dependent glucose dehydrogenase as the recognition element and carbon black as the potential relay station to improve the response time. We find that the enzymatic GRP biosensor rapidly responds to glucose with a good linear relationship between EOC and the logarithm of glucose concentration within a range from 100 µM to 2.65 mM. The GRP biosensor shows high selectivity over O2 and coexisting neurochemicals, good reversibility, and sensitivity and can in vivo monitor glucose dynamics in rat brain. We believe that this study will pave a new platform for the in vivo potentiometric biosensing of chemical events with high reliability.

High-Efficiency and Narrowband Green Thermally Activated Delayed Fluorescence Organic Light-Emitting Diodes Based on Two Diverse Boron Multi-Resonant Skeletons.

Up to now, highly efficient narrowband thermally activated delayed fluorescence (TADF) molecules constructed by oxygen-bridged boron with an enhancing multiple resonance (MR) effect have been in urgent demand for solid-state lighting and full-color displays. In this work, a novel MR-TADF molecule, BNBO, constructed by the oxygen-bridged boron unit and boron-nitrogen core skeleton as an electron-donating moiety, is successfully designed and synthesized via a facile one-step synthesis. Based on BNBO as an efficient green emitter, the organic light-emitting diode (OLED) shows a sharp emission peak of 508 nm with a full-width at half-maximum (FWHM) of 36 nm and realizes quite high peak efficiency values, including an external quantum efficiency (EQEmax) of 24.3% and a power efficiency (PEmax) of 62.3 lm/W. BNBO possesses the intramolecular charge transfer (ICT) property of donor-acceptor (D-A) materials and multiple resonance characteristics, which provide a simple strategy for narrowband oxygen-boron materials.

Ratiometric fluorescent and electrochemiluminescent dual modal assay for detection of 2,6-pyridinedicarboxylic acid as an anthrax biomarker.

2,6-pyridinedicarboxylic acid (DPA) is an excellent biomarker of Bacillus anthracis (B. anthracis). The sensitive detection of DPA, especially through visual point-of-care testing, was significant for accurate and rapid diagnosis of anthrax to timely prevent anthrax disease or biological terrorist attack. Herein, a ratiometric fluorescent (R-FL) and electrochemiluminescent (ECL) dual-mode detection platform with a lanthanide ion-based metal-organic framework (Ln-MOF, i.e., M/Y-X: M = Eu, Y = Tb, and X = 4,4',4″-s-triazine-1,3,5-triyltri-m-aminobenzoic acid) was developed. Eu/Tb-TATAB nanoparticles were constructed to identify DPA. The R-FL detection platform quantitatively detected DPA by monitoring the I545/I617 ratio of the characteristic fluorescence peak intensities of Tb3+ ions and Eu3+ ions. The ECL sensing platform successfully quantified DPA by exploiting the burst effect of DPA on the ECL signal. The above methods had highly sensitive and rapid detection of DPA in water and serum samples. The results showed that this dual-mode detection platform may be projected to be a powerful instrument for preventing related biological warfare and bio-terrorism.

Facile electrochemiluminescence sensing platform based on Gd2O3:Eu3+ nanocrystals for organophosphorus pesticides detection in vegetable samples.

In this work, europium ion-doped gadolinium trioxide nanocrystals (Gd2O3:Eu3+ NCs) were successfully synthesized and applied to construct an electrochemiluminescence (ECL) sensor. Compared with pure Gd2O3, the doping of Eu3+ ions caused enhanced ECL intensity and more stable signals. Based on the excellent ECL performance of Gd2O3:Eu3+ NCs, we constructed a new ECL sensing platform for the detection of organophosphorus pesticides (OPs). The ECL sensor showed a good linear relationship in the concentration range of 1 nM to 1 pM, with a limit of detection of 0.12 pM (S/N = 3) for dichlorvos (DDVP). In addition, the constructed ECL sensor was applied for the detection of DDVP in vegetable samples, and good recoveries were obtained. The results indicated that the ECL sensor exhibited fantastic performance properties and had good application prospects in OPs detection.

Ultralow-background SERS substrates for reliable identification of organic pollutants and degradation intermediates.

Chemical methods for preparing SERS substrates have the advantages of low cost and high productivity, but the strong background signals from the substrate greatly limit their applications in characterization and identification of organic compounds. Herein, we developed a one-step synthesis method to prepare silver nanoparticle substrates with ultralow SERS background using anionic ligands as stabilizing agents and applied the SERS substrate for the reliable and reproducible identification of typical organic pollutants and corresponding degradation intermediates. The synthesis method shows excellent universality to different reducing agents cooperating with different anionic ligands (Cl-, Br-, I-, SCN-). As model applications, the machine learning algorithm can realize the precise prediction of six organophosphorus pesticides and eight sulfonamide antibiotics with 100% accuracy based on SERS training data. More importantly, the ultralow-background SERS substrate enables one to detect and identify the time-dependent degradation intermediates of organophosphorus pesticides by combining them with density functional theory (DFT) calculations. All the results indicate that the ultralow-background SERS substrate will greatly push the development of SERS characterization applications.

A Comparative Study of Nanobio Interaction of Zn-Doped CdTe Quantum Dots with Lactoferrin Using Different Spectroscopic Methods.

In this paper, glutathione (GSH)-coated Zn-doped CdTe quantum dots (QDs) with different particle sizes were synthesized using the "reflow method", and the interaction mechanism between the two QDs and lactoferrin (LF) was investigated systemically with different spectroscopic methods. The steady-state fluorescence spectra showed that the LF formed a tight complex with the two QDs through static bursting and that the electrostatic force was the main driving force between the two LF-QDs systems. The complex generation process was found to be spontaneous (ΔG < 0) and accompanied by exothermic and increasing degrees of freedom (ΔH < 0, ΔS > 0) by using the temperature-dependent fluorescence spectroscopy. The critical transfer distance (R0) and donor-acceptor distance (r) of the two LF-QDs systems were obtained based on the fluorescence resonance energy transfer theory. In addition, it was observed that the QDs changed the secondary and tertiary structures of LF, leading to an increase in the hydrophobicity of LF. Further, the nano-effect of orange QDs on LF is much larger than that of green QDs. The above results provide a basis for metal-doped QDs with LF in safe nano-bio applications.

Preparation of a Red-Emitting, Chitosan-Stabilized Copper Nanocluster Composite and Its Application as a Hydrogen Peroxide Detection Probe in the Analysis of Water Samples.

Hydrogen peroxide (H2O2) is an important reactive oxygen species that mediates a variety of physiological functions in biological processes, and it is an essential mediator in food, pharmaceutical, and environmental analysis. However, H2O2 can be dangerous and toxic at certain concentrations. It is crucial to detect the concentration of H2O2 in the environment for human health and environmental protection. Herein, we prepared the red-emitting copper nanoclusters (Cu NCs) by a one-step method, with lipoic acid (LA) and sodium borohydride as protective ligands and reducing agents, respectively, moreover, adding chitosan (CS) to wrap LA-Cu NCs. The as-prepared LA-Cu NCs@CS have stronger fluorescence than LA-Cu NCs. We found that the presence of H2O2 causes the fluorescence of LA-Cu NCs@CS to be strongly quenched. Based on this, a fluorescent probe based on LA-Cu NCs@CS was constructed for the detection of H2O2 with a limit of detection of 47 nM. The results from this research not only illustrate that the as--developed fluorescent probe exhibits good selectivity and high sensitivity to H2O2 in environmental water samples but also propose a novel strategy to prepare red-emitting copper nanoclusters (Cu NCs) by a one-step method.

Solution-Processable Pure-Red Multiple Resonance-induced Thermally Activated Delayed Fluorescence Emitter for Organic Light-Emitting Diode with External Quantum Efficiency over 20 .

Developing solution-processable red organic light-emitting diodes (OLEDs) with high color purity and efficiency based on multiple resonance thermally activated delayed fluorescence (MR-TADF) is a formidable challenge. Herein, by introducing auxiliary electron donor and acceptor moieties into the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) distributed positions of multiple resonance skeleton simultaneously, an effective strategy to obtain red MR-TADF emitters was represented. The proof-of-the-concept molecule BN-R exhibits a narrowband pure-red emission at 624 nm, with a high luminous efficiency of 94 % and a narrow bandwidth of 46 nm. Notably, the fabricated solution-processable pure-red OLED based on BN-R exhibits a state-of-the-art external quantum efficiency over 20 % with the Commission Internationale de I'Éclairage coordinates of (0.663, 0.337) and a long operational lifetime (LT50 ) of 1088 hours at an initial luminance of 1000 cd m-2 .

Electrochemiluminescence Sensor Based on CeO2 Nanocrystalline for Hg2+ Detection in Environmental Samples.

The excessive concentration of heavy-metal mercury ions (Hg2+) in the environment seriously affects the ecological environment and even threatens human health. Therefore, it is necessary to develop rapid and low-cost determination methods to achieve trace detection of Hg2+. In this paper, an Electrochemiluminescence (ECL) sensing platform using a functionalized rare-earth material (cerium oxide, CeO2) as the luminescent unit and an aptamer as a capture unit was designed and constructed. Using the specific asymmetric matching between Hg2+ and thymine (T) base pairs in the deoxyribonucleic acid (DNA) single strand, the "T-Hg-T" structure was formed to change the ECL signal, leading to a direct and sensitive response to Hg2+. The results show a good linear relationship between the concentration and the response signal within the range of 10 pM-100 µM for Hg2+, with a detection limit as low as 0.35 pM. In addition, the ECL probe exhibits a stable ECL performance and excellent specificity for identifying target Hg2+. It was then successfully used for spiked recovery tests of actual samples in the environment. The analytical method solves the problem of poor Hg2+ recognition specificity, provides a new idea for the efficient and low-cost detection of heavy-metal pollutant Hg2+ in the environment, and broadens the prospects for the development and application of rare-earth materials.

Electrochemiluminescence Aptasensor Based on Gd(OH)3 Nanocrystalline for Ochratoxin A Detection in Food Samples.

In the present study, the electrochemiluminescence (ECL) properties of Gd(OH)3 nanocrystals with K2S2O8 as the cathode coreactant were studied for the first time. Based on the prominent ECL behavior of this material and the excellent specificity of the aptamer technique, an ECL aptasensor for the detection of ochratoxin A (OTA) was formulated successfully. Over an OTA concentration range of 0.01 pg mL-1 to 10 ng mL-1, the change in the ECL signal was highly linear with the OTA concentration, and the limit of detection (LOD) was 0.0027 pg mL-1. Finally, the ECL aptasensor was further used to detect OTA in real samples (grapes and corn) and satisfactory results were obtained, which indicated that the built method is expected to be applied in food detection.

Sensitive and Facile HCOOH Fluorescence Sensor Based on Highly Active Ir Complexes' Catalytic Transfer Hydrogen Reaction.

With several major polarity and weak optical properties, the sensitive detection of HCOOH remains a major challenge. Given the special role of HCOOH in assisting in the catalytic hydrogenation process of Ir complexes, HCOOH (as a hydrogen source) could rapidly activate Ir complexes as catalysts and further reduce the substrates. This work developed a facile and sensitive HCOOH fluorescence sensor utilizing an optimal catalytic fluorescence generation system, which consists of the phenyl-pyrazole-type Ir-complex PP-Ir-Cl and the coumarin-type fluorescence probe P-coumarin. The sensor demonstrates excellent sensitivity and specificity for HCOOH and formates; the limits of detection for HCOOH, HCOONa, and HCOOEt3N were tested to be 50.6 ppb, 68.0 ppb, and 146.0 ppb, respectively. Compared to previous methods, the proposed sensor exhibits good detection accuracy and excellent sensitivity. Therefore, the proposed HCOOH sensor could be used as a new detection method for HCOOH and could provide a new design path for other sensors.

Toxicity Assessment of the Binary Mixtures of Aquatic Organisms Based on Different Hypothetical Descriptors.

Modern industrialization has led to the creation of a wide range of organic chemicals, especially in the form of multicomponent mixtures, thus making the evaluation of environmental pollution more difficult by normal methods. In this paper, we attempt to use forward stepwise multiple linear regression (MLR) and nonlinear radial basis function neural networks (RBFNN) to establish quantitative structure-activity relationship models (QSARs) to predict the toxicity of 79 binary mixtures of aquatic organisms using different hypothetical descriptors. To search for the proper mixture descriptors, 11 mixture rules were performed and tested based on preliminary modeling results. The statistical parameters of the best derived MLR model were Ntrain = 62, R2 = 0.727, RMS = 0.494, F = 159.537, Q2LOO = 0.727, and Q2pred = 0.725 for the training set; and Ntest = 17, R2 = 0.721, RMS = 0.508, F = 38.773, and q2ext = 0.720 for the external test set. The RBFNN model gave the following statistical results: Ntrain = 62, R2 = 0.956, RMS = 0.199, F = 1279.919, Q2LOO = 0.955, and Q2pred = 0.855 for the training set; and Ntest = 17, R2 = 0.880, RMS = 0.367, F = 110.980, and q2ext = 0.853 for the external test set. The quality of the models was assessed by validating the relevant parameters, and the final results showed that the developed models are predictive and can be used for the toxicity prediction of binary mixtures within their applicability domain.

A novel electrochemiluminescence sensor based on a molecular imprinting technique and UCNPs@ZIF-8 nanocomposites for sensitive determination of imidacloprid.

As an efficient and easily available pesticide, imidacloprid (IM) has been widely used in agriculture to kill pests. However, threats to the ecological environment are becoming increasingly prominent, caused by abuse and pesticide residues. This paper reports a sensitive electrochemiluminescence (ECL) sensor based on upconverting nanoparticle functional zeolite imidazolate framework (UCNPs@ZIF-8) nanocomposites combined with molecularly imprinted polymers (MIPs) to successfully achieve the quantitative detection of IM. The composites exhibited a certain multi-faceted prismatic structure and the effective binding of UCNPs was demonstrated by characterization technology. In addition, a sensor with MIPs/UCNPs@ZIF-8/GCE as the working electrode exhibited outstanding ECL performance, including a strong and stable signal and excellent selectivity under optimal conditions. This sensor showed a good linear response to IM over a wide concentration range (0.1 ng L-1-1 mg L-1), with a limit of detection as low as 0.01 ng L-1. More significantly, it was successfully applied to the determination of IM concentration levels in food, which provides broad application prospects for the construction of pesticide ECL sensors.

A Novel Turn-On Fluorescent Sensor Based on Sulfur Quantum Dots and MnO2 Nanosheet Architectures for Detection of Hydrazine.

In this paper, the SQDs@MnO2 NS as the probe was applied to construct a novel "turn-on" fluorescent sensor for sensitive and selective detection of hydrazine (N2H4). Sulfur quantum dots (SQDs) and MnO2 nanosheets (MnO2 NS) were simply mixed, through the process of adsorption to prepare the architectures of SQDs@MnO2 NS. The fluorescent emissions of SQDs@MnO2 NS play a key role to indicate the state of the sensor. According to the inner filter effect (IFE) mechanism, the state of the sensor at the "off" position, or low emission, under the presence of MnO2 NS, is which the ultraviolet and visible spectrum overlaps with the fluorescence emission spectrum of SQDs. Under the optimal conditions, the emission was gradually recovered with the addition of the N2H4, since the N2H4 as a strong reductant could make the MnO2 NS converted into Mn2+, the state of the sensor at the "on". Meanwhile, the fluorescent sensor possesses good selectivity and high sensitivity, and the detection concentration of N2H4 with a wide range from 0.1 µM to 10 mM with a detection limit of 0.072 µM. Furthermore, actual samples were successful in detecting certain implications, indicating that the fluorescent sensor possesses the potential application ability to monitor the N2H4 in the water.

Self-luminescent europium based metal organic frameworks nanorods as a novel electrochemiluminescence chromophore for sensitive ulinastatin detection in biological samples.

In this work, we developed a novel electrochemiluminescence (ECL) biosensor for ulinastatin (UTI) detection based on self-luminescent metal-organic framework (L-MOF) nanomaterials. The L-MOFs could be simply prepared by one-pot methods using Eu3+ and 4,4',4″-s-triazine-1,3,5-triyltri-m-aminobenzoic acid (H3TATAB) as the metallic center and organic ligand, respectively. The Eu-TATAB exhibited high efficiency and stable ECL performance when using K2S2O8 as coreactant. For the established biosensor, Eu-TATAB was both used as the ECL chromophore and protein carrier due to its outstanding biocompatibility and large superficial area, which could load sufficient antibodies to link with antigen in the biosensor for subsequent detection. The established sandwich ECL biosensor showed a wide linear range of 0.1 ng mL-1 - 105 ng mL-1 and a low limit of detection of 9.7 pg mL-1 for UTI detection. In addition, the developed ECL biosensor could also be successfully applied to the real UTI sample determination in serum. The reported biosensor strategy could provide a guide for developing more other novel and promising high-performance ECL nanomaterials, and also be used as a potential method for ultrasensitive UTI detection in disease research.

Selective Detection of Alkaline Phosphatase Activity in Environmental Water Samples by Copper Nanoclusters Doped Lanthanide Coordination Polymer Nanocomposites as the Ratiometric Fluorescent Probe.

In this paper, a novel, accurate, sensitive and rapid ratiometric fluorescent sensor was fabricated using a copper nanoclusters@infinite coordination polymer (ICP), specifically, terbium ion-guanosine 5'-disodium (Cu NCs@Tb-GMP) nanocomposites as the ratiometric fluorescent probe, to detect alkaline phosphatase (ALP) in water. The fluorescence probe was characterized by scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy. The experimental results showed that, compared with Tb-GMP fluorescent sensors, Cu ratiometric fluorescent sensors based on NCs encapsulated in Tb-GMP had fewer experimental errors and fewer false-positive signals and were more conducive to the sensitive and accurate detection of ALP. In addition, the developed fluorescent probe had good fluorescence intensity, selectivity, repeatability and stability. Under optimized conditions, the ratiometric fluorescent sensor detected ALP in the range of 0.002-2 U mL-1 (R2 = 0.9950) with a limit of detection of 0.002 U mL-1, and the recovery of ALP from water samples was less than 108.2%. These satisfying results proved that the ratiometric fluorescent probe has good application prospects and provides a new method for the detection of ALP in real water samples.

A portable visual coffee ring based on carbon dot sensitized lanthanide complex coordination to detect bisphenol A in water.

In this work, a ratiometric fluorescence sensor along with a portable coffee ring visualized detection method for bisphenol A (BPA) was developed based on carbon dots. The probe was formed by the coordination polymerization of Eu3+ and 5'-adenosine monophosphate on the surface of carbon dots containing a large number of hydroxyl and carbonyl groups. The results showed that the fluorescence intensity ratio and the concentration of BPA had a good linear relationship in a wide range of 0.1-100 µM with a detection limit of 20 nM (S/N = 3). The recoveries of the added standard BPA in water samples ranged from 91.80 to 102.7% with relative standard deviation values no more than 1.84% (n = 3). In addition, the changes of the fluorescence color of the CDs@Eu-AMP suspension with different BPA concentrations can be easily visualized under a UV lamp by the naked eye, which highlights the great potential of the coffee ring detection method for the fast and convenient monitoring of BPA in real water samples.

An ultrasensitive electrochemiluminescence biosensor for the detection of total bacterial count in environmental and biological samples based on a novel sulfur quantum dot luminophore.

In this paper, the electrochemiluminescence (ECL) of sulfur quantum dots (SQDs) in a potassium persulfate cathodic co-reactant was studied. Based on the selective quenching of the ECL emission from the SQDs by ß-nicotinamide adenine dinucleotide (NADH), an ultrasensitive ECL biosensor with NADH as an important parameter was established for the highly sensitive and selective detection of total bacterial count (TBC). A linear response between the ECL intensity and the NADH concentration in the range of 1 pM to 10 µM was obtained, thus achieving a detection limit of 1 pM. As the content of NADH in cells is positively correlated with the TBC, a sensor has been successfully applied to detect the TBC in actual water samples with a good recovery rate of 103-107 CFU mL-1. This study provides a green and feasible method for TBC detection in the environment.

Electrochemiluminescent determination of CYFRA21-1 serum levels using Ti-Fe-O nanotubes immunoassay.

Prominent electrochemiluminescence (ECL) in Ti-Fe-O nanotube arrays (Ti-Fe-O NTs) with K2S2O8 as the cathode coreactant is reported for the first time. Compared with pure titanium dioxide nanotubes (TiO2 NTs), this heterojunction could effectively reduce the band gap, facilitate electronic transitions, and move the ECL potential to a positive direction. The ECL performance motivated the development of an ultrasensitive ECL immunosensor for detecting cytokeratin fragment 21-1 (CYFRA21-1). Magnetic beads loaded with conductive carbon black (CCB/MNTs) were used to efficiently quench the ECL signal of a Ti-Fe-O NTs electrode and were combined with an ECL immunoassay to realize sensitive detection of CYFRA21-1. Over a CYFRA21-1 concentration range of 1.0 pg·mL-1 ~ 100 ng·mL-1, the change in the ECL signal was highly linear with the logarithm of the CYFRA21-1 concentration, and the limit of detection (LOD) was 0.114 pg·mL-1. This ECL immunosensor was used to successfully determine the CYFRA21-1 content in serum. The recovery of CYFRA21-1 in actual serum was 88.6 - 104.4%, and the RSD was 1.4 - 3.0%. The coreaction solution used in this work was PBS (0.1 M, pH = 7.4) containing 0.05 M K2S2O8, the scanning range was -1.0 - 0 V, the photomultiplier tube (PMT) was set to 750 V, and the scanning rate was 100 mV·s-1.

Encapsulating Ru(bpy)32+ in an infinite coordination polymer network: Towards a solid-state electrochemiluminescence sensing platform for histamine to evaluate fish product quality.

In this work, we demonstrate a novel solid-state electrochemiluminescence (ECL) sensor based on the Ru(bpy)32+@terbium-guanosine monophosphate infinite coordination polymer network ((Ru(bpy)32+@Tb-GMP ICPn). Comparing with the traditional luminescence of Ru(bpy)32+ observed in a liquid system, the proposed method of encapsulating Ru(bpy)32+ into ICPn for immobilization greatly improves the ECL signal and efficiency, which is attributed to the unique porous structure and large specific surface area of ICPn. Moreover, the solid-state Ru(bpy)32+ ECL sensor has good biocompatibility and low toxicity. Taking histamine (HA) as a detection model, a good linear relationship between ECL intensity and logarithm of HA concentration was obtained with a low detection limit of 17 nM, and satisfactory results were obtained for detecting HA levels in fish samples as well. The proposed solid-state Ru(bpy)32+ ECL sensor has great application prospects in the safety of food.