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Hematite concentration is an important climatic proxy for environmental (climatic) studies of soils and sediments. However, the accurate quantification of naturally occurring hematite has always been a difficult question, especially for those areas with lower hematite concentrations. Diffuse reflectance spectroscopy (DRS) is an effective method for hematite identification and quantification with lower detection limits. In this study, we synthesized a set of samples with well-determined concentrations to explore the exact detectable range of hematite and propose the most effective transfer function between the DRS proxy and hematite concentration. In addition, natural sediments from Inland Asia and the Western Pacific Ocean were used to further test the feasibility of the new transfer function. Results show that the lowest DRS detection limit for hematite could reach ~0.00078%, but is affected by the natural matrix. We also find that the second derivative of the Kubelka–Munk (K–M) function is monotonically correlated with the hematite concentration (0.00078%–100%), but ambiguities exist for the first derivative. Therefore, the second derivative of the K–M function is highly suggested for the hematite quantification, especially when concentration exhibits a wide range of variations. This study provides important references for the application of hematite proxy and promotes the popularization and development of the DRS method. [ABSTRACT FROM AUTHOR]

In this paper, nanoparticles decorated Ce 2 (WO 4) 3 nanosheets (CWNSs) with negative potential and large specific surface area were synthesized and developed as highly efficient peroxidase mimics for colorimetric detection of H 2 O 2. CWNSs can efficiently catalyze the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) in the presence of H 2 O 2 to induce an obvious color variation. Kinetic analysis indicated that the catalytic behaviors of CWNSs obey the typical Michaelis-Menten mechanism. The peroxidase-like catalytic mechanism of CWNSs was proposed according to the active species trapping experiments, verifying that ·O 2 – radicals played primary roles in the catalytic reaction. Based on the strong and stable peroxidase-like catalytic activity of CWNSs, a simple, rapid, selective, and ultrasensitive method was successfully established for colorimetric detection of H 2 O 2. The method has a good linear response ranging from 0.5 μM to 100 μM for H 2 O 2 concentration with a lower detection limit of 0.15 μM. Benefitting from the sensitive response and good stability, the method is applied in real sample detection and shows a favorable reproducibility and feasibility. This work not only provides a novel enzymatic mimics with remarkable catalytic activities for biomedical and environmental analysis, but also extends the application area of Ce 2 (WO 4) 3 materials. Unlabelled Image • Ce 2 (WO 4) 3 nanosheets were developed as highly efficient peroxidase mimics for colorimetric detection of H 2 O 2 firstly. • CWNSs possessed a nice peroxidase-like activity owing to the negative potential and large specific surface area. • CWNSs exhibited a stronger binding affinity with TMB compared to HRP. • A rapid and ultrasensitive method was established for detecting H 2 O 2 based on CWNSs with a detection limit of 0.15 μM. • The sensing system revealed a high selectivity, stability and reusability. [ABSTRACT FROM AUTHOR]

In this article, a novel triphenylamine-modified salicylaldehyde Schiff base 2-(((4-(diphenylamino)phenyl)imino)methyl)-4-(pyridine-4-yl)phenol (HL) was synthesized and structurally characterized. HL possessed D–π-A structure and exhibited typical AIE property in THF/H2O. It was applied to selectively recognize Cu2+ through an on–off mode in THF/H2O (1/9, v/v), and the fluorescence attenuation was attributed to a paramagnetic quenching effect of Cu2+ together with the abatement of HL aggregates. Hence, the detection limit achieved was as low as 1.32 × 10−7 M. The spectroscopic and ESI-HRMS results revealed a 1 : 2 complexation ratio of Cu2+ with HL. The mechanism for sensing Cu2+ was further confirmed by performing DFT calculations. Owing to the large affinity between Cu2+ and His, the resultant CuL2 system was further used to detect His via the off–on method based on the displacement of ligands. The detection limit for His reached 5.14 × 10−8 M. Furthermore, HL was available to prepare handy indicator papers for the on-site recognition of Cu2+ and His. Confocal fluorescent imaging demonstrated that HL could sequentially respond to intracellular Cu2+ and His. [ABSTRACT FROM AUTHOR]

In this work, we designed and synthesized a novel multifunctional molecule, (E)-2-(4-(diphenylamino)styryl)-5-(4-pyridyl)-8-quinolinol (HL), which possessed D-π-A structure and exhibited optical responses to acid-base vapor and Zn(II) ions. Zn(II) complex of HL (W1) was obtained and characterized by SC-XRD. Spectral experiments demonstrated that complex W1 displayed aggregation-induced emission enhancement (AIEE) property, which was exact opposite to the aggregation-caused quenching effect of HL. The quantum yield of W1 (15%) was much higher than that of HL (2.1%) in the solid state. Both HL and complex W1 involved sp2 hybrid N atoms, whose protonation and deprotonation gave rise to reversible acidochromism with high contrast. The mechanism was clarified by XPS, 1H NMR, infrared spectroscopy, elemental analysis, PXRD and thermogravimetry results. Benefiting from excited state intramolecular proton transfer in HL together with AIEE of W1 , HL could recognize Zn(II) sensitively in aqueous media. The detection limit of HL for Zn(II) reached as low as 5.02 × 10−8 M. An anti-counterfeiting application was realized using HL -loaded test strip, which exhibited fluorescence response, but no color change upon exposure to Zn(II) solution. In addition, HL and W1 solids were combined to develop a stimuli induced encryption/decryption strategy successfully based on their reversible acidochromic behaviors. [Display omitted] • A triphenylamine derivative with D-π-A structure was synthesized and displayed multistimuli photoresponsive behavior. • Its Zn(II) complex exhibited AIE and reversible acidochromism characters. • The mechanisms for these photoresponsive behaviors were clarified via a series of experiments. • Test strip and information encryption/decryption applications were realized based on these stimuli-responsive properties. [ABSTRACT FROM AUTHOR]

An original dual signal amplification immunoassay for N-Terminal pro-brain natriuretic peptide (NT-proBNP) detection is developed based on Au NPs and Zn doped CdS nanoparticles (Zn 0.02 Cd 0.98 S) co-sensitized Bi 2 MoO 6 nanosheet photoelectrochemical (PEC) platform, the target is a good myocardial marker for diagnosing heart failure (HF). Bi 2 MoO 6 as an outstanding photocatalysis material is successfully used in PEC analysis in this work, and the nanosheet structure provide a preponderance to capture superior Zn 0.02 Cd 0.98 S in order to achieve anticipant PEC response. The doping of Zn makes the energy band of CdS matched more compatible with Bi 2 MoO 6 , and improves the narrow band gap of CdS, making the surface plasma resonance (SPR) effect of Au NPs more significant, thus further improving the PEC response, as well as elevated the detection sensitivity of biological targets. The constructed PEC platform for NT-proBNP provides a wide detection range of 0.0001–1000 ng mL−1 and gives the minimum detection value of 0.037 pg mL−1. Great stability, high selectivity, and good reproducibility are also achieved. The proposed PEC immunoassay provides more possibilities for other protein ultra-sensitivity detection. Image 1 • A novel PEC immunosensor for ultrasensitive detection of NT-proBNP was proposed based on photosensitive Bi 2 MoO 6 matrix. • The doped of Zn was successfully preferred the band gap of CdS with Bi 2 MoO 6. • The band gap of CdS after modification played a great role in the SPR effect of Au NPs. • The biosensor for NT-proBNP exhibited the detection limit of 0.037 pg mL−1. [ABSTRACT FROM AUTHOR]

Combining of amperometric and square wave voltammetric methods (SWV), the dual-signal sandwich electrochemical immunosensor was developed for quantitative determination of amyloid β-protein (Aβ). Cu was doped into Al 2 O 3 lattice (Cu–Al 2 O 3) and reacts with graphite carbon nitride (g-C 3 N 4) to generate Cu–Al 2 O 3 -g-C 3 N 4 with internal dual-reaction center structure, which has good catalytic properties of hydrogen peroxide (H 2 O 2). Subsequently, palladium nanoparticles (Pd NPs) was introduced into Cu–Al 2 O 3 -g-C 3 N 4 (Cu–Al 2 O 3 -g–C 3 N 4 –Pd) that not only synergistically catalyzed H 2 O 2 but also immobilized anti-Aβ (Ab 1) via Pd–NH 2. The Cu–Al 2 O 3 -g–C 3 N 4 –Pd was used as matrix material to modify the electrode, which can produce obviously electrochemical signals through Amperometry i-t curve. Meanwhile, the Zr 6 O 4 (OH) 4 (CO 2) 12 (UiO-66) modified with polyaniline (PANI) has the large specific surface, good conductivity and adsorption capacity, which can support methylene blue (MB) as signal label of anti-Aβ (Ab 2). Therefore, the UiO-66@PANI-MB can provide an obviously electrochemical signal about MB through SWV. Under optimal conditions, the dual-signal sandwich electrochemical immunosensor has salient analytical performance and both signal platforms provide more accurate results. The linear range of detection obtained by the immunosensor was 10 fg/mL-100 ng/mL, and the detection limit was 3.3 fg/mL. This method not only provided a reliable guarantee for the experimental detection but also provided an effective strategy for the detection of other biological. Cu–Al 2 O 3 -g–C 3 N 4 –Pd catalyze H 2 O 2 to generate electrochemical signal and UiO-66@PANI-MB can produce the peak current through Amperometry i-t curve, which together constructed the dual-signal sandwich electrochemical immunosensor. Image 1 • A dual-signal sandwich electrochemical immunosensor was fabricated. • Cu–Al 2 O 3 -g–C 3 N 4 –Pd owned excellent properties for catalyzing hydrogen peroxide. • UiO-66@PANI-MB was used as a novel signal label. • The electrochemical immunosensor utilized SWV and Amperometry i-t curve. • The designed immunosensor exhibited low detection limit of 3.3 fg/mL for Aβ. [ABSTRACT FROM AUTHOR]

In this study, a ratiometric electrochemical immunosensor has been developed to detect the cytokeratin 19 fragment 21–1 (CYFRA21-1) biomarker in a highly sensitive manner through a dual-signal output model. As one of signal indicators, snowflake-like FeSe 2 loaded with AuNPs (FeSe 2 -AuNPs) as sensing substrate with good conductivity and large active sites provides a differential pulse voltammetry (DPV) signal at +0.4 V. Another signal indicator, toluidine blue (TB) with the water-solubility property is an excellent redox probe that can generate DPV signal at −0.3 V. To solve the water-solubility problem, the TB is absorbed with polyacrylic acid (PAA) functionalized ZIF-67 (PAA-ZIF-67), which retains the properties of ZIF-67 that are large specific surface area and strong adsorption properties. The ratio of signals, stemmed from PAA-ZIF@TB and FeSe 2 -AuNPs (I PAA-ZIF@TB /I FeSe2-AuNPs), increases with the CYFRA21-1 concentration. Under optimal experimental conditions, CYFRA21-1 was detected in a wide dynamic range from 0.1 pg/mL to 100 ng/mL, with a lower limit of detection of 0.02 pg/mL. Looking ahead, this ratio based strategy provides prospective clinical applications for detecting other biomarkers. [Display omitted] • Snowflake-like FeSe 2 -AuNPs produces DPV signal at +0.4 V of the immunosensor. • PAA functionalized ZIF-67 adsorbed TB (PAA-ZIF@TB) produces a DPV signal at −0.3 V. • The ratio of two DPV signals produced by the sensor is linear with the antigen. • The sensor shows an ultra-low detection limit of 0.02 pg/mL for CYFRA21-1. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Ultrasensitive electrochemical aptasensor was developed for detecting Pb2+. • Au@p-rGO was applied as support for immobilizing the aptamer. • Au NPs@GO as signal probe exhibited high electrocatalytic activity towards H 2 O 2. • The aptasensor displayed low detection limit of 1.67 pmol/L for Pb2+. Abstract A sensitive electrochemical aptasensor was designed based on gold modified graphene nanocomposite with different morphologies for the detection of lead ion (Pb2+). Specifically, a sulfydryl-labeled substrate strand (Apt1) and a sulfydryl-labeled catalytic strand (Apt2) were devised in fabricating the electrochemical aptasensor. Gold modified porous reduced graphene oxide (Au@p-rGO) was synthesized and applied as support for immobilizing the Apt1. And gold modified graphene oxide (Au NPs@GO) was employed as signal probe and connected with Apt2 to realize the immobilization of it on the electrode by means of the principle of complementary base pairing. The current signal can be obtained by recording the electrocatalytic conditions toward H 2 O 2. The Pb2+-dependent DNAzyme could play a role when Pb2+ existed. With the increase of the concentration of Pb2+, the current response revealed a diminishing signal, thus realizing the sensitive detection of Pb2+. Under the optimal conditions, the fabricated electrochemical aptasensor exhibited a linear response toward Pb2+ ranging from 5 pmol/L to 1 μmol/L, together with a low limit of detection of 1.67 pmol/L. Moreover, the prepared aptasensor displayed outstanding selectivity, acceptable stability and superior reproducibility for detecting Pb2+. This proposed tactics may provide reference and potential applications for detecting some other heavy metal ions. [ABSTRACT FROM AUTHOR]

Biocompatible nitrogen-doped hydrazide-conjugated carbon dots (NHCDs) as an anodic luminophores with low excitation potential were equipped with an efficient multiple signal-amplification strategy for electrochemiluminescence (ECL) trace bioanalysis. To promote the ECL emission of NHCDs-H 2 O 2 system, gold nanoparticles (Au NPs) functionalized tin oxide nanocrystals (Au@SnO 2 NCs) were adopted to anchor large amount of NHCDs, the formed NHCDs-Au@SnO 2 NCs could conjugate with detection antibody as the signal label. Moreover, 3,4,9,10-perylenetetracarboxylic acid (PTCA) molecules were immobilized on the flower-like microsphere (PTCA@ZnCo 2 O 4 /ZnO) nanocomposites to fabricate as an electro-active sensing substrate to incubate the capture antibody, which could efficiently accelerate the generation of reactive oxygen species (OH · /O 2 ·- ) through electrocatalytic excitation and co-reaction acceleration. Integrating with the sandwich-type sensing model, an ECL immunosensor was established to detect biomarkers of squamous cell carcinomas named cytokeratin 19 fragments (cyfra21–1). Combining with the synergistic signal-amplification induced by the Au@SnO 2 NCs, PTCA, and ZnCo 2 O 4 /ZnO nanocomposites, the developed immunosensor performed detection range from 0.09 pg/mL to 100 ng/mL with a detection limit of 34.38 fg/mL. The results showcased the great potential of this sensing strategy for real sample analysis of biomarker with reliable stability, selectivity and repeatability. • Flower-like PTCA-modified ZnCo 2 O 4 /ZnO was synthesized by hydrothermal method. • PTCA-modified ZnCo 2 O 4 /ZnO was demonstrated that can efficiently achieve electrocatalytic excitation and catalyze the ROSs production to amplify the ECL signal. • Au@SnO 2 NCs was utilized to construct highly efficient catalytic nanocarriers. • Signal multiple-amplification strategy was built to improve sensitivity. • The established immunosensor exhibited low detection limit of 34.38 fg·mL-1 for CYFRA21-1. [ABSTRACT FROM AUTHOR]

In order to realize the ultra sensitive detection of Neuron specific enolase (NSE) in human serum, we chose electrochemical immunosensor as a simple analytical method. During the experiment, we found that the peak value signals of Cu-MOFs-Au and Fc- L -Cys were significantly changed at −0.20 V and 0.20 V potentials by DPV. So a ratiometric electrochemical immunosensor for quantitative analysis of NSE was prepared for Cu-MOFs-Au as the electrode sensing surface and Fc- L -Cys as the label of Ab 2. The data and performances of the immunosensor were tested and analyzed by DPV. Cu-MOFs not only provide the required signal for the immunosensor, but also have a large specific surface area, which can provide more sites for the placement of Au nanoparticles. L -cysteine (L -Cys) can prevent a large amount of Fc-COOH leakage, so that Fc+ can stably provide another required signal. With the beefing up of NSE concentration, redox peak of Cu-MOFs-Au decreased and that of Fc- L -Cys raised. The ratio (ΔI=ΔI Cu /ΔI Fc) of two different signals was linear with the logarithm of NSE concentration in a certain value range. In brief, with the optimized experimental conditions, the immunosensor showed excellent performance in the concentration range of 1 pg/mL to 1 μg/mL, and the detection limit was 0.011 pg/mL. Compared with other immunosensors, it showed an unexpected high sensitivity. This method also provided a new idea for the ultra sensitive quantitative detection of other biomarkers. Cu-MOFs-Au and Fc- L -Cys form a ratiometric electrochemical immunosensor through the electrochemical response signals generated by DPV at different potentials. [Display omitted] • An ultrasensitive ratiometric electrochemical immunosensor for quantitative analysis of NSE was developed. • Sandwich ratiometric electrochemical immunosensor improved sensitivity. • The electrochemical response signals generated by Cu-MOFs-Au and Fc- L -Cys at different potentials were used as the basis for the construction of ratiometric electrochemical immunosensor. • The established immunosensor exhibited low detection limit of 0.011 pg/mL for NSE. [ABSTRACT FROM AUTHOR]

• CoOOH was used as the ECL quencher probe for the first time. • A new ECL-RET donor-receptor was proposed and fabricated for ultrasensitive detection of PCT. • Dual-quenching system was built to improve sensitivity. • NH 2 -MIL-101 conjugated with g-C 3 N 4 to increase its biocompatibility and emission performance. • The established immunosensor exhibited low detection limit of 3.4 fg mL−1 for PCT. Herein, an ultrasensitive electrochemiluminescence (ECL) biosensing platform for early diagnosis of procalcitonin (PCT) was developed based on enhancing the stability of ECL signal and dual-quenching strategies. In this proposal, in order to improve the deficient of luminescence signal stability of semiconductor luminescent materials, the chromophore graphitic carbon nitride (g-C 3 N 4) was loaded onto the MOF material (amine-functionalized MIL-101: NH 2 -MIL-101). Due to the excellent catalytic performance of NH 2 -MIL-101, more ECL reaction intermediate SO 4 - are restored from the co-reactant S 2 O 8 2-, thus the ECL signal of g-C 3 N 4 becomes stronger and more stable. With the aim of achieving detection of trace markers and improving sensor sensitivity, the dual-quenching strategy is carried out, which was achieved as follows: (i) the strong energy transfer between the donor of g-C 3 N 4 @NH 2 -MIL-101 and the acceptor of cobalt oxyhydroxide nanoflakes@gold nanoparticle (CoOOH@Au NPs) rational diminishes the ECL signal of g-C 3 N 4 ; (ii) the perfect spectral overlap with the luminescent matrix achieves efficiency quenching through resonance energy transfer (RET). Benefiting from the ultrastability of luminophore and the reasonable dual quenching effect, the fabricated ECL biosensor presented dominant stability, selectivity and reproducibility accompanied by detection ranges from 0.014 pg/mL to 40 ng/mL and extremely low detection limit of 3.4 fg/mL. Consequently, it is worth believing that this method can provide a potential analytical strategy for trace immunoassay in clinical analysis. [ABSTRACT FROM AUTHOR]

Procalcitonin (PCT) as a disease marker is of great significance in the early diagnosis of septicemia and pyemia. Biosensor have good prospects for analysis and detection of disease markers, but developing highly sensitive detection methods for detecting PCT remains a daunting task. In this paper, we develop a ratiometric electrochemical immunosensor with Au NPs modified SiO 2 -Fc-COOH complex as matrix and UiO-66 loaded with Toluidine blue (TB) as a marker for quantitative detection of procalcitonin (PCT). The SiO 2 modified by APTES not only has a large specific surface area but also contains abundant amino groups, which can be connected to the electrochemical probe of ferrocenecarboxylic acid (Fc-COOH). UiO-66 has the advantages of large specific surface area, high porosity and adjustable structure, which can adsorb toluidine blue electrochemical probe through electrostatic attraction. Measurement and analysis of the prepared immunosensor by Differential Pulse Voltammetry (DPV) show that the oxidation peak currents of Fc-COOH and TB appear at potentials of 0.30 V and −0.30 V respectively. As the PCT concentration increases, the oxidation peak current of TB increases and the oxidation peak current of Fc-COOH decreases. The ratios (ΔI = ΔI TB /ΔI Fc-COOH) between the double signals could show a certain linear relationship with the concentration of the PCT within a certain range. Under optimal conditions, the linear range of detection obtained by the immunosensor was 1 pg/mL-100 ng/mL and the detection limit was 0.3 pg/mL. In this work, the developed ratiometric electrochemical immunosensor not only provides a simple, reliable and sensitive strategy for quantitative detection of PCT but also provides a useful method for clinical detection of other disease markers. • A ratiometric electrochemical immunosensor was fabricated. • The electrochemical immunosensor utilized DPV. • SiO 2 -Fc–COOH–Au and UiO-66-TB were used as electrochemical signal probes. • The designed immunosensor exhibited low detection limit of 0.3 pg/mL for PCT. [ABSTRACT FROM AUTHOR]

Heme binds to amyloid β -peptide (A β) in the brain of Alzheimer΄s disease (AD) patients, thus forming heme-A β complexes and leading the characteristic pathological features of AD. The heme-A β complexes reduce O 2 by 2e− to obtain co-reactant H 2 O 2. In this work, two-dimensional graphite-like carbon nitride (g-C 3 N 4) was hybridized with heme via π-π interaction to construct an electrochemiluminescence (ECL) biosensor for detection of A β peptides. The capture aptamer was firstly immobilized on the gold electrode, and then incubated with target A β peptides and g-C 3 N 4 -heme. The g-C 3 N 4 -heme-A β composite was subsequently anchored on the electrode and showed a signal-on, label-free ECL emission based on dual co-reactants enhancement attributed to in-situ generated H 2 O 2 and original K 2 S 2 O 8 in PBS buffer. Under the optimum experimental conditions, the ECL biosensor has a sensitive response to A β peptides with a linear range of 10 fM-0.1 μM and a detection limit of 3.25 fM. Considering prominent specificity, reproducibility, and stability, the proposed biosensor was used to assess recovery of A β peptides in human serum and the result was satisfactory. We believe that the established method would offer a useful analytical means for quantifying A β peptides in a biological matrix. [ABSTRACT FROM AUTHOR]

• Ultrasensitive electrochemical aptasensor was fabricated for detecting Pb2+. • AuPd@Fe-MOFs labeled DNA was firstly applied to produce the electrical signal. • Au@MoS 2 /rGO was utilized as sensing platform to construct the aptasensor. • The aptasensor displayed low detection limit of 0.07 pmol/L for Pb2+ detection. In this work, an electrochemical aptasensor was proposed by using gold-modified molybdenum disulfide/reduced graphene oxide (Au@MoS 2 /rGO) nanocomposite and gold-palladium (AuPd)-modified MIL-88 (Fe) metal-organic frameworks (AuPd@Fe-MOFs) for sensitive detection of lead ions (Pb2+). The 8–17 DNAzyme consisting of a substrate strand (Apt1) and a catalytic strand (Apt2) was used to construct the aptasensor. Au@MoS 2 /rGO nanocomposite was applied as the sensing platform to immobilize the mercapto-group-labeled Apt1. Meanwhile, AuPd@Fe-MOFs was employed to label Apt2, which showed excellent catalytic ability toward H 2 O 2. In the presence of Pb2+, the Apt1 of the DNAzyme was catalytically cut off, decreasing the amount of AuPd@Fe-MOFs. The current response was correlated to the Pb2+concentration, thereby achieving Pb2+ detection. Under the optimal experimental conditions, the fabricated aptasensor showed a highly linear response for Pb2+ in the range from 5.0 pmol/L to 2.0 μmol/L, with a detection limit of 0.07 pmol/L. Additionally, the proposed electrochemical aptasensor exhibited excellent selectivity, stability and reproducibility. Moreover, the proposed aptasensor demonstrated good performance in real water sample analysis, making it promising for use in Pb2+ detection in environmental monitoring. [ABSTRACT FROM AUTHOR]

In this work, a "signal-off" sandwich electrochemiluminescence (ECL) immunosensor was fabricated for ingenious detection of Alzheimer's disease marker β-amyloid (Aβ) based on dual metal-organic frameworks (dual-MOFs), which included NH 2 -UiO-66 and MIL-101. Dual-MOFs with high porosity and plentiful functional groups can increase the biomolecules binding rate, and through the synergy with the different materials can effectively amplify the inherent properties of the material itself. Ru(bpy) 3 2+ was capsulated in NH 2 -UiO-66 as luminophor, the complex possessed steady and excellent luminescence efficiency as well as large specific surface area to load sufficient antibodies. MoS 2 quantum dots (MoS 2 QDs) combined with MIL-101 via Au–S bond. MIL-101@Au–MoS 2 QDs was used for the label of secondary antibodies (Ab 2) to quench the ECL signal of Ru(bpy) 3 2+/NH 2 -UiO-66. The amount of Ab 2 -MIL-101@Au–MoS 2 QDs bound to antigen will gradually accrue with the increase of the concentration of Aβ, which led to "signal-off" for accurate estimation of Aβ. Under optimal conditions, the developed assay for Aβ detection demonstrated a wide linear range of 10−5 ng mL−1 to 50 ng mL−1 and the detection limit was as low as 3.32 fg mL−1 (S/N = 3). The cooperation of dual-MOFs has potential as a universal strategy for quantitative analysis of other targets. Ru(bpy) 3 2+ and MoS 2 QDs simultaneously reacted with tripropylamine (TPA) to consume the co-reactant in the PBS solution, resulting in "Signal off". Image 1 • Dual-MOFs were applied to ECL signal amplification and annihilation. • A "signal-off" method for detecting Aβ was developed. • Ru(bpy) 3 2+/NH 2 -UiO-66 existed excellent ECL signal. • The quenching mechanism of MoS 2 to Ru(bpy) 3 2+ was firstly proposed. [ABSTRACT FROM AUTHOR]

• A novel PEC signal amplification assay was presented for sensitivity PCT detection. • Zn x Bi 2 S 3+x were used as the sensitizer through the SILAR method modified on to NiTiO 3 rod surface. • The proposed immunosensor owns a large linear range of 0.0005–50 ng mL−1 with a 0.18 pg mL-1 detection limit. • The signal amplification strategy provide applicable to other targets PEC immunosensors. An original signal amplification photoelectrochemical (PEC) immunosensor for procalcitonin detection was fabricated based on Zn x Bi 2 S 3+x sensitized NiTiO 3 nanorods. Using ethylene glycol as medium, the NiTiO 3 nanorods were successfully manufactured after calcination in air atmosphere, the rod-like structure have rough surface that produced benefit to capture lots of functional Zn x Bi 2 S 3+x , the sensitizer sensitized NiTiO 3 on ITO substrate by means of a sequential ionic layer adsorption reaction, and the obtained Zn x Bi 2 S 3+x /NiTiO 3 composites showed an excellent absorption of visible light owing to the matched band gap. By the way, Zn x Bi 2 S 3+x /NiTiO 3 composites as mimic enzyme of glucose oxidase, high sensitivity was achieved due to the generated H 2 O 2 as holes scavenger when glucose added, that promote the photo electrons transfer quickly, further increased the PEC signal. The as prepared sensor showed a large linear range of 0.0001–50 ng·mL−1 with 0.04 pg·mL−1 detection limit. Simultaneously, the signal amplification strategy of this sensor provides applicable to other PEC immunosensors for detection of other targets. [ABSTRACT FROM AUTHOR]

• We systematically synthesis a series of well-defined nanocomposites, like dumbbell-style AuPd and dendrite-like AuPt. • The Au 3 Pd 4 and Au 3 Pt 3 possess excellent catalysis, which can improve the current response of Au 3 Pd 4 /GCE and Au 3 Pt 3 /GCE. • This is the first time that a list of dumbbell-style AuPd modified GCEs to detect nitrite and dendrite-like AuPt modified GCEs to detect TBHQ. • Au 3 Pd 4 /GCE and Au 3 Pt 3 /GCE sensors can respectively detect nitrite and TBHQ with wide linear range and low detection limit. The paper reported the controlled synthesis of dumbbell-style AuPd and dendrite-like AuPt by a simple seed-mediated growth method, respectively. The composition and performances of the resulting nanomaterials were measured using transmission electron microscopy (TEM), high-resolution TEM (HRTEM), UV–vis absorption spectroscopy (UV–vis), X-ray photoelectron spectroscopy (XPS) and electrochemical methods. Moreover, the dumbbell-style AuPd modified glassy carbon electrode (GCE) showed excellent electrocatalytic ability towards nitrite with a fairly wide concentration range from 2 μM to 4200 μM and a 0.67 μM detection limit. The dendrite-like AuPt modified GCE showed excellent electrocatalytic ability towards tert-butyl hydroquinone (TBHQ) with a linear range from 0.35 μM to 625 μM and a relatively low detection limit of 0.075 μM. The electrochemical testing results exhibited the two kinds of sensors, Au 3 Pd 4 /GCE and Au 3 Pt 3 /GCE, possessed accepted selectivity, long-term stability and good reproducibility. Thus, the proposed two sensors could be applied in the determination of food samples. It is expected that the unique AuPd and AuPt are promising materials, which have great potential application in many fields of clinical diagnosis, new energy technologies, catalysis and sensors. [ABSTRACT FROM AUTHOR]

An electrochemiluminescence (ECL) analytical platform was proposed for ultrasensitive detection of amyloid-β proteins (Aβ) based on the ECL resonance energy transfer (ECL-RET). In this work, gold nanoparticles-functionalized graphitic carbon nitride nanosheets (g-C 3 N 4 @Au NPs) and palladium nanoparticles-coated Metal organic framework (Pd NPs@NH 2 -MIL-53) were synthesized, which were as ECL donor and ECL acceptor respectively. A strong cathode ECL emission was obtained from the g-C 3 N 4 @Au NPs when used K 2 S 2 O 8 as its co-reactant. Here, Au NPs not only was used as an accelerator to enhance and stabilize the ECL signal, but also a connector for attaching Aβ antibody. In addition, NH 2 -MIL-53(Al) was selected as a label material for supporting Pd NPs to synergistically increase the intensity and range of UV-visible absorption. The ECL signal of g-C 3 N 4 @Au NPs was intensely decreased when the ECL acceptor probe Pd NPs@NH 2 -MIL-53 was incubated onto the modified GCE by way of the specific recognition. Under the optimal condition, a wide detection range from 10 fg/mL to 50 ng/mL and a low detection limit of 3.4 fg/mL (S/N = 3) were obtained. In consideration of favorable specificity, stability and reproducibility, the proposed method was successfully applied for Aβ detection in actual human serum samples and could be a potential analytical tool for sensitive molecular trace detection in clinical analysis. • A new ECL-RET donor-receptor was proposed and fabricated for ultrasensitive detection of Aβ. • Au NPs conjugated with g-C 3 N 4 to increase its biocompatibility and emission performance. • Pd NPs coated NH 2 -MIL-53(Al) was used as the ECL quencher probe for the first time. • The designed immunosensor exhibited low detection limit of 3.4 fg mL-1 for Aβ. [ABSTRACT FROM AUTHOR]