Potential Applications In Bioanalysis Research Articles

Proximity hybridization induced bipedal DNA walker and rolling circle amplification for label-free electrochemical detection of apolipoprotein A4

Apolipoprotein A4 (Apo-A4) is considered as a prospective molecular biomarker for diagnosis of depression due to its neurosynaptic toxicity. We develop a proximity hybridization-induced DNAzyme-driven bipedal DNA walker strategy for Apo-A4 quantification based on rolling circle amplification (RCA) triggered by poly adenine binding to Ag nanoparticles (AgNPs). With the help of DNAzyme, the free-running bipedal DNA walker can quickly and sequentially shear a molecular beacon that acts as a primer to initiate the RCA process, producing a large number of long DNA strands containing numerous adenines. The long repetitive adenine strands then absorb large amounts of AgNPs on the electrode interface, which is then electrochemically stripped of the AgNPs. The method has a linear detection range of 0.001 ∼ 100 ng mL−1 and a detection limit of 0.46 pg mL−1. The presented detection strategy is label-free, which allows high sensitivity and selectivity for detection of a wide range of protein targets by corresponding DNA-based affinity probes, which have potential applications in bioanalysis.

A fluorescence-electrochemiluminescence dual-mode sensor based on a "switch" system for highly selective and sensitive K-ras gene detection

Herein, an fluorescence (FL)−electrochemiluminescence (ECL) dual-mode biosensor is constructed based on the dual-signal “turn-on” strategy of functionalized metal-organic frameworks nanosheets (RuMOFNSs)-tetraferrocene for K-ras gene detection, and the mechanism of bursting through front-line orbital theory is explained for the first time. Amino-functionalized tetraferrocene-labeled probe DNA molecules are linked to RuMOFNSs by covalent amide bonds, acting as FL and ECL intensity switches. The target DNA, complementary to the probe DNA, triggers cyclic amplification of the target by nucleic acid exonuclease III (Exo III), repelling tetraferrocene reporter groups away from RuMOFNSs and inhibiting the electron transfer process and photoinduced electron transfer (PET) effect. These phenomena induce a double turn-on of FL and ECL signals with a high signal-to-noise ratio. The developed FL-ECL dual-mode sensing platform provides sensitive detection of the K-ras gene with detection limits of 0.01 fM (the detection range is 1 fM to 1 nM) and 0.003 fM (the detection range is 0.01 fM to 10 pM), respectively. In addition, the proposed dual-mode sensor can be easily extended to detect other disease-related biomarkers by changing the specific target and probe base sequences, depicting potential applications in bioanalysis and early disease diagnosis.

High-throughput, modular and logic analysis platform based on binary photonic crystals array and entropy-driven amplifier for multiplex biomarkers detection

The development of high-throughput and modular assay of multiplex biomarkers has great significance for disease diagnosis but it still faces some difficulty. Herein, a high-throughput, modular and logic analysis platform combining binary photonic crystals (PCs) array and entropy-driven DNA amplifier (EDA) was developed to achieve simple, high-sensitive, and nonenzymic detection of multiplex biomarkers. In this platform, three modules including logic-recognition, EDA and binary PCs array were integrated, and each module had independent and universal design but connected functions. The binary PCs array was fabricated conveniently through stacking self-assembly of two kinds of colloidal nanospheres, and could specifically enhance two kinds of fluorescence based on the match between emission peak and photonic band gap. Functionally, the input of two mRNA biomarkers initiated the logical operation of logic-recognition module, and the released DNA strand triggered corresponding EDA module for amplified fluorescence signal output (FAM or Cy5). The whole DNA circuit was performed in one step. Then, binary PCs array module further enhanced both two fluorescence signals, and got direct fluorescence signal readout by microplate reader (scanning rate of 96 samples/ 7 min). It is the first time that the binary PCs array-based high-throughput platform has achieved logical and sensitive detection of multi-biomarkers by employing logic gate and EDA. Therefore, the proposed platform has merits of logical analysis, high sensitivity, programmable design, high throughput and multiplex detection, showing potential application in bioanalysis and clinical diagnostics.

Electrochemiluminescence immunoassay strategies based on a hexagonal Ru-MOF and MoS2@GO nanosheets: detection of 5-fluorouracil in serum samples.

Herein, a competitive-type electrochemiluminescence immunosensor for ultrasensitive detection of 5-fluorouracil (5-FU) was fabricated. Ruthenium(II)-metal-organic framework (Ru-MOF) nanosheets were selected to act a promising ECL luminophore using tris(4,4'-dicarboxylic acid-2,2'-bipyridyl) ruthenium(II) dichloride (Ru(dcbpy)32+) as the organic ligand. The two-dimensional (2D) Ru-MOF nanosheets achieved an increased loading of Ru(dcbpy)32+ and effectively prevented leakage of the ECL emitter during application, which exhibited satisfactory ECL performance. Thin two-dimensional MoS2@GO was used to modify the electrode as the sensing platform for improving the electron transfer rate and loading more 5-FU coating antigens due to its large specific surface area and piezoelectric catalytic efficiency. Under the optimized conditions, the proposed immunosensor presented high sensitivity, a wide detection range (0.0001 ng-100 ng mL-1), a low limit of detection (0.031 pg mL-1, S/N = 3), good specificity and stability. Furthermore, the immunosensor was successfully applied for the detection of 5-FU in human serum samples with satisfactory results, proving this strategy has potential applications in bioanalysis and clinical diagnosis.

Label-free homogeneous photoelectrochemical aptasensing of VEGF165 based on DNA-regulated peroxidase-mimetic activity of metal-organic-frameworks

The application of metal-organic frameworks (MOFs) nanozymes in biosensing has been extensively investigated, however, till now there is still no report on photoelectrochemical (PEC) sensing based on enzyme memetic properties of MOFs. To further expand the utilization of MOFs nanozymes in biosensing, we developed a label-free homogenous PEC aptasensor for the detection of VEGF165, an important cancer biomarker, based on the DNA-regulated peroxidase-mimetic activity of Fe-MIL-88, a type of MOFs. In this strategy, the peroxidase-mimetic property of MOFs is integrated with the label-free homogeneous PEC sensing approach, and highly sensitive detection of VEGF165 is obtained with a detection limit down to 33 fg/mL, superior or comparable to the previously reported values. Moreover, this approach displays outstanding specificity, and has been successfully used to detect VEGF165 added in diluted serum samples. As far as we know, it is the first example to employ the peroxidase-like activity of MOFs in PEC biosensing, which may find potential application in bioanalysis and early disease diagnosis.

Upconversion encoded microcarriers from electrospray microfluidics for multiplex bioassays

Encoded microcarriers are powerful tools in bioanalysis since they facilitate the detection of multiple targets during a single test. A current trend of developing encoded microcarriers is endowing them with features of easy coding/decoding, large coding capacity, and less restriction from usage conditions. Here, we presented novel upconversion nanoparticles (UCNPs)-encapsulated microcapsules derived from electrospray microfluidics as encoded microcarriers. The UCNPs offered a convenient optical coding/decoding mechanism; by encapsulating UCNPs into separate compartments of microcapsules via microfluidics, a large coding capacity was achieved. Most prominently, the unique anti-Stokes luminescent feature of the UCNPs made them less restricted from penetration depth of the excitation light. Benefiting from these merits, the microcarriers have demonstrated their value as barcodes for multiplex immunoassays. We believe this novel microcarrier could find potential applications in bioanalysis and biodiagnostic fields.

Target-induced ratiometric electrochemical aptasensor for highly sensitive detection of thrombin based on AuNPs-MXene

Development of specific and sensitive electrochemical sensing platform for thrombin (TB) analysis is highly desirable for its important roles in many diseases. Herein, we designed and explored a facile ratiometric electrochemical aptasensor for TB detection based on signal on–off strategy. AuNPs-MXene was synthesized, characterized, and used to functionalize the basic electrode as a signal-amplified sensing platform. Hairpin probe (Hp) labeled with ferrocene (Fc) as signal probe, TB aptamer (TBA) labeled with methyl blue (MB) as capture probe are rationally introduced to fabricate highly-selective recognition and ratiometric dual-signal readout aptasensor. The sequence of Fc-Hp was designed to be complementary with MB-TBA to form a double-stranded DNA structure. When TB is present, the specific interaction between MB-TBA and TB leads to the departure of MB-TBA and the formation of hairpin structure of Fc-Hp, resulting in the leaving away of MB and confining Fc group near the electrode surface. Consequently, the oxidation peak current (Ipa) of Fc increased (signal-on), meanwhile Ipa of MB decreased (signal-off). Thus, the specific recognition of MB-TBA to TB can be read out in an electrochemical signal on–off ratiometric mode. A novel ratiometric electrochemical aptasensor was constructed with a wide linear range of 5.0 fmol/L ∼ 1.0 pmol/L and a low detection limit of 1.7 fmol/L (3S0/S). Moreover, this ratiometric electrochemical aptasensor shows excellent selectivity, outstanding sensitivity, and good stability in real serum sample analysis, exhibiting promising potential application in bioanalysis.

Synthesis of KCl-doped lignin carbon dots nanoenzymes for colorimetric sensing glutathione in human serum

A KCl-doped lignin carbon dots (K,Cl-LCDs) nanoenzymes was successfully synthesized by hydrothermal method to construct a sensor for detecting glutathione (GSH). Sodium lignosulfonate with a lot of oxygen-containing functional groups as a carbon precursor can provide effective active sites, and KCl as a dopant can influence the charge distribution on the surface of CDs. In the enzyme catalyzing progress, K,Cl-LCDs with peroxidase-like activity can oxidize 3,3,5,5-tetramethylbenzidine (TMB) into blue oxTMB with the presence of H2O2, the absorbance of the system at 652 nm changed consequently. When GSH is introduced into the system, the reducibility of GSH restores oxTMB to colorless. So that, a sensor for colorimetric detection of GSH is constructed. In addition, through free radical experiments, the catalytic mechanism was explored, confirming that the reaction was induced by hydroxyl radicals (·OH). The sensor has a low detection limit (0.08 μM) for detecting GSH with good linear range (0.25–25 μM). The sensor system was applied to the determination of GSH concentration in human serum samples with the recoveries of 98.2%− 103.2% and RSDs of 2.3%− 4.7%. The proposed sensor for GSH detection has the advantages of simple operation, low cost, and high speed, indicating its potential application in bioanalysis.

Highly Selective and Sensitive microRNA-210 Assay Based on Dual-Signaling Electrochemical and Photocurrent-Polarity-Switching Strategies.

Highly sensitive and selective microRNA (miRNA) assay is of great significance for disease diagnosis and therapy. Herein, a magnetic-assisted electrochemistry (EC)-photoelectrochemistry (PEC) dual-mode biosensing platform was developed for miRNA-210 detection based on dual-signaling EC and photocurrent-polarity-switching PEC strategies. Porous magnetic Fe3O4 octahedra with a large surface area were synthesized by calcining Fe-based metal-organic frameworks. Subsequently, the magnetic photoelectric materials (Fe3O4@CdS) were developed by the successive ionic layer adsorption and reaction method in Cd2+ and S2- solutions. Then, the self-assembled DNA nanoprisms contained three thiols/hanging arms that could capture miRNA-210 efficiently and were anchored to the Fe3O4@CdS octahedra via the Cd-S bond. When miRNA-210 was present, the double-stranded DNA concatemers [the self-assembled duplex helixes based on a pair of methylene blue (MB)-labeled single-stranded DNAs (AP1 and AP2) through the hybridization chain reaction and then intercalated with adriamycin (Dox) into their grooves] were connected with the Fe3O4@CdS-DNA nanoprisms. MB and Dox not only acted as the electrochemical probes but also synergistically switched the photocurrent polarity of the Fe3O4@CdS octahedra. Thus, miRNA-210 was assayed sensitively and selectively via the proposed EC-PEC dual-mode biosensing platform. Additionally, the abovementioned recognition steps occurred in a homogeneous system, and the effects of the impurities and interferences on the miRNA-210 assay could be easily avoided by magnetic separation due to the good magnetic properties of Fe3O4 octahedra. The proposed EC-PEC dual-mode biosensing platform showed a wide range of potential applications in bioanalysis and early diagnosis of disease.

Assembled molecular beacon-based self-propelled DNA machine for enzyme-free and distinctly amplified nucleic acid detection

Abstract Sensitive nucleic acid detection by simple, rapid, cost-effective and enzyme-free amplified strategy is continually pursued for its extensive applications in bioanalysis and clinical disease diagnosis. Herein, an assembled molecular beacon-based self-propelled DNA machine was proposed for enzyme-free and distinctly amplified nucleic acid detection. The sensing system was consisted of three different DNA subunits and an assembled molecular beacon (aMB). Owing to the facile and programmable signal output of aMB, current strategy demonstrated two-level signal amplification capability for target detection: 1) target-triggered assembly unit could circularly dissociate aMB for the first-level signal amplification; 2) the liberated DNA sequence from the aMB could work as target analogy, contributing to the cascade and self-propelled signal amplification toward target DNA. The whole sensing system was well characterized by rational design of control experiments. The advantages of such sensing system also include assay simplicity (one-step mixing process) and no participation of protein enzyme. An attractive detection performance toward nucleic acid target (low detection limit of 10 fM, linear range of 0.1 pM-0.1 nM) could be achieved. It was also suitable for nucleic acid analysis in the relatively complicated biological matrix such as serum. Thus, current assembled molecular beacon-based DNA machine might be explored to develop various sensing systems for the potential applications in bioanalysis and clinical disease diagnosis.

Self-assembled zeolitic imidazolate framework-8/Ag nanoparticles composite with well-controlled flower-like architectures for ultrasensitive surface-enhanced Raman scattering detection

The performance of surface-enhanced Raman scattering (SERS) active substrates highly depends on its structure and components. Herein, for the first time, a novel zeolitic imidazolate framework-8 (ZIF-8)/Ag nanoparticles composite with flower-like architecture is demonstrated. By using tannic acid as structure-directing agent, well-controlled flower-like ZIF-8 could be obtained. Through in-situ reduction, Ag nanoparticles with uniform grain distribution were directly grown on the surface of ZIF-8 nanosheets. The synergy effects of preconcentration and plasmonic hot spot allow the picomolar detections and high reproducibility of the SERS method. As a result, the minimum detection limit of rhodamine 6G can be as 10−14 mol L−1 and the stability and repeatability are satisfactory. This work provides a facile and general method to develop plasmonic ZIF-8 hybrid with controlled morphology for potential applications in bioanalysis, chemical sensing and catalysis.

Flower-like metal-organic framework microsphere as a novel enhanced ECL luminophore to construct the coreactant-free biosensor for ultrasensitive detection of breast cancer 1 gene

Nowadays, serious restriction by aggregation quenching and proton attack in aqueous media, electrochemiluminescence (ECL) signals of emitter hardly match the requirement of ultrasensitive biomedical detection in practice. In this work, a novel flower-like metal-organic framework microsphere was formed by chelating Zn ion with carboxyl-rich tris(4,4′-dicarboxylic acid-2,2′-bipyridyl) ruthenium(II) (Ru(dcbpy)32+) in the presence of cetyltrimethylammonium bromide (CTAB), defined as ZnMOF(Ru) for simplicity. For that, the obtained ZnMOF(Ru) as a high-performance ECL emitter displayed 53-fold amplification in aqueous solution without any coreactant alternative to that of Ru(dcbpy)32+, coupled with the dramatically enhanced fluorescence quantum yield and stability of the intermediates. Thus, a “sandwich”-like ECL biosensor was developed for detecting breast cancer 1 gene (BRCA1), showing the wide linear range (1.0 fM–0.1 nM) and ultralow limit of detection (LOD) down to 0.71 fM. Hence, this work provides a universal and robust pattern to develop advanced ECL luminophores and exploit their potential applications in bioanalysis.

Peptide cleavage-mediated photoelectrochemical signal on-off via CuS electronic extinguisher for PSA detection

In this work, a peptide-based photoelectrochemical (PEC) biosensor was constructed based on CdTe/TiO2 sensitized structure as electrode and CuS nanocrystals as signal amplifier for the ultrasensitive detection of protein. After peptide was fixed to the CdTe/TiO2 electrode surface, the double-helix DNA (dsDNA) was immobilized at the end of the peptide and used as a carrier to immobilize the doxorubicin-copper sulfide nanocrystals (Dox-CuS) conjugates. As a proof of concept, prostate specific antigen (PSA) has been chosen as the model. In absence of PSA, CuS nanocrystals could consume electron donors and exciting light energy. Additionally, the steric hindrance effect of biomacromolecules hindered the movement of electron donors to the photoelectrode. Eventually, the photoelectric response signal was reduced, and the biosensor was in a "signal off" state. When PSA existed, the PSA specifically cleaved the peptide, and DNA/Dox-CuS probes were released from the electrode surface, resulting in a "signal on" state. The PEC biosensor revealed good specificity, stability, and reproducibility, and it exhibited excellent application in PSA analysis with a linear range from 0.005 to 20ngmL-1 and a low detection limit of 0.0015ngmL-1. This PEC biosensor may have potential applications in bioanalysis, disease diagnostics, and clinical biomedicine.

Ultrasensitive Immunosensor for Cardiac Troponin I Detection Based on the Electrochemiluminescence of 2D Ru-MOF Nanosheets.

Electrochemiluminescence (ECL)-functionalized metal-organic frameworks (MOFs) have attracted increasing attention in biosensing in virtue of their diverse and tunable optical properties. A famous ECL luminophore, carboxyl-rich tris(4,4'-dicarboxylic acid-2,2'-bipyridyl) ruthenium(II) (Ru(dcbpy)32+), possesses the characteristics of good water solubility and excellent ECL performance and also has the potential to be the organic ligand of metal-organic frameworks. Herein, functionalized MOF nanosheets (RuMOFNSs) containing plenty of Ru(dcbpy)32+ in the frameworks were synthesized in aqueous solution by a simple one-pot method. In this protocol, Ru(dcbpy)32+ acted as organic ligand to coordinate with Zn2+ originated from Zn(NO3)2, and polyvinylpyrrolidone (PVP) was used as structure-directing agent to control the formation of sheetlike structure. For practical application, a "signal-on" ECL immunosensor was designed for cardiac troponin I (cTnI) detection by employing RuMOFNSs as ECL probe. The immunosensor exhibited high sensitivity and excellent selectivity for cTnI detection in the range from 1 fg/mL to 10 ng/mL with a detection limit as low as 0.48 fg/mL. Finally, the biosensor was successfully applied for the detection of cTnI in human serum sample with satisfactory results, demonstrating its potential application in bioanalysis and clinical diagnosis.

Coupling of Fluorophores in Single Nanoapertures to Tamm Plasmon Structures.

Metal nanostructures (such as plasmonic antennas) have been widely demonstrated to be excellent devices for beaming and sorting the fluorescence emission. These effects rely on the constructive scattering or diffraction from different elements (such as metal corrugations or nanorings) of the nanostructures. However, subwavelength-size nanoholes, without nearby nanoscale features, results in an angularly dispersed emission from the distal surface. Herein, we demonstrate for the first time the emission redirection capabilities of a single isolated nanoaperture milled in a thick silver film deposited on a dielectric multilayer. Specifically, we show that a dye dissolved in ethanol filling in the nanoaperture can couple to Tamm Plasmon Polariton (TPP) modes of the structure. Due to the small in-plane wavevectors of the TPPs, the fluorescence from Tamm-coupled dyes within the nanoaperture is emitted normally to the sample surface, with a minimum angular width of about 12.54°. This kind of fluorescence manipulation has proven to be effective with various nanoaperture shapes, such as circles, squares, and triangles. Our work is also the first experimental demonstration of lateral coupling of fluorophores with TPPs in nanoholes, with potential applications in bioanalysis and biosciences.

Green synthesis of Pd nanocones as a novel and effective electrochemiluminescence illuminant for highly sensitive detection of dopamine

Electrochemiluminescence (ECL) has attracted significant interest because of its superior properties and potential applications in bioanalysis, and therefore many luminescent nanomaterials have been developed. Herein, well-defined Pd nanocones (Pd NCs) were facilely obtained by a one-pot hydrothermal method with poly-l-lysine (PLL) as a green protecting ligand, which were mainly characterized by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Then, the as-obtained Pd NCs were first explored as an anodic ECL emitter, where tripropylamine (TPA) worked as the coreactant to boost the ECL emission. The possible ECL mechanism of Pd NCs/TPA system was extensively explored by ECL and electrochemical techniques. Briefly, the ECL emission underwent the oxidation-reduction route, in which both Pd NCs and TPA were initially oxidized, and then the oxidized TPA lost an proton to form reducing agent (TPA·) strongly reacted with the oxidized Pd NCs generating Pd NCs* for the emission. Furthermore, using dopamine (DA) as an ECL quencher, an ultrasensitive sensor was constructed for DA detection. The fabricated ECL sensor shows high sensitivity and selectivity, good stability, and wide linear range with the low detection limit of 0.46 pM. It offers a new avenue to exploit ECL illuminant and enriches the ECL emission theory.

Co3O4/CuO hollow nanocage hybrids with high oxidase-like activity for biosensing of dopamine

Here, we report the synthesis, characterization, and oxidase-like activity of Co3O4/CuO hollow nanocage (HNC) nanocomposites. The Co3O4/CuO HNCs were successfully prepared by hydrothermal treatment of ZIF-67 in copper nitrate solution, followed by carbonization in air. The obtained nanocomposites were characterized by scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. The Co3O4/CuO HNCs possess enhanced oxidase-like activity compared with pure Co3O4 and CuO, and they can catalytically oxidize the 3,3′,5,5′-tetramethylbenzidine (TMB) substrate in the absence of H2O2 to produce an intense blue product. Reactive oxygen species (ROS) measurements indicate that 1O2 and O2− radicals are the major ROS in catalytic oxidation of TMB by dissolved oxygen in the TMB–Co3O4/CuO HNC system. We then developed a simple, sensitive, visual, and colorimetric biosensing method for dopamine (DA) based on its inhibiting effect on TMB oxidation. The proposed method allows for DA detection with a limit of detection of 0.027 μM and a dynamic range of 0.05–8 μM. This new colorimetric method was successfully used to detect DA in biological samples. The present work demonstrates a simple strategy to fabricate an efficient oxidase mimic with potential applications in bioanalysis and clinical diagnosis.

Layer-by-layer assembled gold nanoparticles/lower-generation (Gn≤3) polyamidoamine dendrimers-grafted reduced graphene oxide nanohybrids with 3D fractal architecture for fast, ultra-trace, and label-free electrochemical gene nanobiosensors

Three layer-by-layer (LBL) assembled gold nanoparticles (AuNPs)/lower-generation (Gn≤3) polyamidoamine dendrimer (PD) with reduced graphene oxide (rGO) as the core/mercaptopropinoic acid (MPA)/Au were successfully fabricated and employed as electrochemical gene nanobiosensing platforms with three-dimensional (3D) fractal nanoarchitecture for fast, ultra-trace determination of label-free DNA hybridization. Three Gn≤3PD were initially grafted to graphite oxide (GO) via the covalent functionalization between amino terminals of PD and carboxyl terminals of GO where a concomitant reduction of GO, which were covalently linked onto MPA that was self-assembled onto Au substrate, and finally AuNPs were encapsulated onto GG1PD by strong physicochemical interaction between AuNPs and -OH of rGO in GG1PD, Their morphologies, structures, electrochemical properties, and gene nanobiosensing performances were characterized and evaluated. AuNPs/GG2PD-based probe displayed the best excellent structural stability, lowest mobility on solid surface with the increasing charge resistance, widest linear range (1.1 × 10−6 – 1 × 10−18), and the lowest limit of detection (1.87 × 10−19 M) in comparison with both AuNPs/GG1PD-based and AuNPs/GG3PD-based probes. This work will provide a new candidate for the development of metal nanoparticles functionalized PD with inorganic nonmetallic nanomaterials as cores with 3D fractal nanoarchitecture and promising electrochemical gene nanobiosensing platforms based on dendrimer-nanoinorganic hybrids with 3D nanoarchitectures and LBL assembly for fast and ultra-trace detection of label-free DNA hybridization with potential application in bioanalysis and medical diagnosis of genetic diseases.

Co3O4–Au Polyhedra: A Multifunctional Signal Amplifier for Sensitive Photoelectrochemical Assay

Taking the zeolitic imidazolate framework (ZIF-67) as the precursor, p-type semiconducting Co3O4-Au polyhedra were synthesized and used as the signal amplifier to construct a sensitive photoelectrochemical (PEC) sensor for caspase-3 activity assay. Here, the n-type semiconductor Bi2S3-modified indium-tin oxide (ITO) slice was used as the photoelectrode. After immobilization of the biotin-DEVD-peptide (biotin-Gly-Asp-Gly-Asp-Glu-Val-Asp-Cys) onto the Bi2S3 surface, the streptavidin-labeled Co3O4-Au polyhedra were introduced to the sensing platform via the specific interaction between biotin and streptavidin. The Co3O4-Au polyhedra can not only quench the photocurrent of the Bi2S3 because of the competitive consumption of electron donors and exciting light energy (p-n-type semiconductor quenching effect), but also act as peroxidase mimetics to produce catalytic precipitate. Additionally, the steric hindrance effect from the Co3O4-Au polyhedra will decrease the PEC response of the Bi2S3. Ingeniously, the precipitates can not only deposit on the ITO electrode to decrease the photocurrent of PEC sensor, but also act as electron acceptors to scavenge the photogenerated electrons of Co3O4-Au polyhedra, leading to enhanced quenching ability of the Co3O4-Au polyhedra. When caspase-3 exists, caspase-3 can specifically recognize and cleave the biotin-DEVD-peptide, resulting in the increase of PEC response. Based on the multifunctional Co3O4-Au polyhedra, caspase-3 is detected sensitively with a linear range from 0.5 to 50 ng mL-1 and limit of detection down to 0.10 ng mL-1. The Co3O4-Au polyhedra provide a novel signal amplifier to construct PEC sensing platform and may have potential applications in bioanalysis, disease diagnostics, and clinical biomedicine.

Facile synthesis of hollow microspherical YPO 4 : Eu 3+ /Tb 3+ using polystyrene spheres as sacrificial template and its photoluminescent properties

Monodisperse hollow microspherical YPO4:Ln3+ (Ln3+ = Eu3+/Tb3+) with diameters of around 2.5 µm have been successfully synthesised by combining a convenient homogeneous precipitation method, an ion exchange method, and a calcination process for the first time. X-ray diffraction, Fourier transform infrared, thermogravimetric analysis, scanning electron microscopy, transmission electron microscopy, and photoluminescence spectra were used to characterise the samples. Upon ultraviolet excitation, Eu3+- and Tb3+-doped microspherical YPO4 showed typical red and green emission, respectively, which provide potential applications in bioanalysis, future colour displays, light-emitting devices, and so on.