Novel Magnetic Fe₃O₄@CdSe Composite Quantum Dot-Based Electrochemiluminescence Detection of Thrombin by a Multiple DNA Cycle Amplification Strategy

A novel small magnetic electrochemiluminescent Fe₃O₄@CdSe composite quantum dot (QD) was facilely prepared and successfully applied to sensitive electrochemiluminescence (ECL) detection of thrombin by a multiple DNA cycle amplification strategy for the first time. The as-prepared composite QDs feature intense ECL, excellent magnetism, strong fluorescence, and favorable biocompatibility, which offers promising advantages for ECL biosensing. ECL of the composite QDs was efficiently quenched by gold nanoparticles (NPs). Taking advantages of the unique and attractive ECL and magnetic characteristics of the composite QDs, a novel DNA-amplified detection method based on ECL quenching was thus developed for a sensitive assay of thrombin. More importantly, the DNA devices by cleavage reaction were cycled multiple rounds, which greatly amplified the ECL signal and much improve the detection sensitivity. This flexible biosensing system exhibits not only high sensitivity and specificity but also excellent performance in real human serum assay. The present work opens a promising approach to develop magnetic quantum dot-based amplified ECL bioassays, which has wider potential application with more favorable analytical performances than other ECL reagent-based systems. Moreover, the composite QDs are suitable for long-term fluorescent cellular imaging, which also highlights the promising directions for further development of QD-based in vitro and in vivo imaging materials

Versatile Electrochemiluminescence Assays for Cancer Cells Based on Dendrimer/CdSe–ZnS–Quantum Dot Nanoclusters

In this work, a novel dendrimer/CdSe–ZnS–quantum dot nanocluster (NC) was fabricated and used as an electrochemiluminescence (ECL) probe for versatile assays of cancer cells for the first time. A large number of CdSe–ZnS–quantum dots (QDs) were labeled on the NCs due to the many functional amine groups within the NCs, which could significantly amplify the QD’s ECL signal. Capture DNA was specially designed as a high-affinity aptamer to the target cell; a novel ECL biosensor for cancer cells was directly accomplished by using the biobarcode technique to avoid cross-reaction. Moreover, magnetic beads (MBs) for aptamers immobilization were combined with the dendrimer/QD NCs probe for signal-on ECL assay of cancer cells, which greatly simplified the separation procedures and favored for the sensitivity improvement. In particular, a novel cycle-amplifying technique using a DNA device on MBs was further employed in the ECL assay of cancer cells, which greatly improved the sensitivity. To the best of our knowledge, this is the first study that the novel dendrimer/QD NCs probe combined with a DNA device cycle-amplifying technique was employed in the ECL assays of cells. Excellent discrimination against target and control cells is demonstrated, indicating that the ECL assays have great potential to provide a sensitive, selective, cost-effective, and convenient approach for early and accurate detection of cancer cells

Multifunctional Photoelectrochemical Biosensor Based on ZnIn₂S₄/ZnS QDs@Au–Ag-Reversed Photocurrent of Cu-Metal–Organic Framework Coupled with CRISPR/Cas-12a-Shearing for Assay of Dual Targets

False positives and negatives in bioanalytical assays remain a persistent problem. Herein, a multifunctional photoelectrochemical (PEC) biosensor based on ZnIn2S4 (ZIS)/ZnS quantum dots (QDs)@Au–Ag-reversed photocurrent of Cu-metal–organic framework (MOF) coupled with CRISPR/Cas-12a-shearing was innovatively developed for assay of dual targets. First, Cu-MOF as a good PEC material shows cathodic photocurrent. Then, numerous ZIS/ZnS QDs were assembled to the Au–Ag nanoparticles (NPs) to prepare a stable and highly amplified signal probe, which can just match the energy level of Cu-MOFs and realized the polarity-reversed photocurrent of Cu-MOF for the first time. As the empty-core nanostructure of Au–Ag NPs has a high specific surface area and low material density, the bimetallic nanocrystal can much increase the reaction rate and improve the redox efficiency. When target CEA-produced cDNA opened the hairpin DNA (HP1 DNA) on the electrode, the ZIS/ZnS QDs@Au–Ag signal probe was conjugated to the electrode via DNA hybridization, achieving a significantly reversed PEC current for CEA detection. Moreover, the specific binding of kanamycin/aptamer generated the acDNA (activator), which can activate the trans-cleavage activity of the CRISPR-CAS12a system on ssDNA, so the signal probe was sheared and caused the obvious decrease of PEC signal for kanamycin detection. The newly developed ZIS/ZnS QDs@Au–Ag NPs displayed excellent PEC properties and reversed photocurrent to MOF and were combined with the unique CRISPR-Cas12a system to achieve sensitive detection of dual targets, which can open a new polarity-reversed PEC sensing platform for rapid and accurate analysis of multiple targets and can effectively avoid false positives results in clinical testing

Spatial-Potential-Color-Resolved Bipolar Electrode Electrochemiluminescence Biosensor Using a CuMoOx Electrocatalyst for the Simultaneous Detection and Imaging of Tetracycline and Lincomycin

A spatial-potential-color-resolved bipolar electrode electrochemiluminescence biosensor (BPE-ECL) using a CuMoOx electrocatalyst was constructed for the simultaneous detection and imaging of tetracycline (TET) and lincomycin (LIN). HOF-101 emitted peacock blue light under positive potential scanning, and CdSe quantum dots (QDs) emitted green light under negative potential scanning. CuMoOx could catalyze the electrochemical reduction of H2O2 to greatly increase the Faradic current of BPE and realize the ECL signal amplification. In channel 1, CuMoOx-Aptamer II (TET) probes were introduced into the BPE hole (left groove A) by the dual aptamer sandwich method of TET. During positive potential scanning, the polarity of BPE (left groove A) was negative, resulting in the electrochemical reduction of H2O2 catalyzed by CuMoOx, and the ECL signal of HOF-101 was enhanced for detecting TET. In channel 2, CuMoOx-Aptamer (LIN) probes were adsorbed on the MXene of the driving electrode (DVE) hole (left groove B) by hydrogen-bonding and metal-chelating interactions. LIN bound with its aptamers, causing CuMoOx to fall off. During negative potential scanning, the polarity of DVE (left groove B) was negative and the Faradic current decreased. The ECL signal of CdSe QDs was reduced for detecting LIN. Furthermore, a portable mobile phone imaging platform was built for the colorimetric (CL) detection of TET and LIN. Thus, the multiple mode-resolved detection of TET and LIN could be realized simultaneously with only one potential scan, which greatly improved detection accuracy and efficiency. This study opened a new technology of BPE-ECL sensor application and is expected to shine in microchips and point-of-care testing (POCT)

CdS Nanocrystal-Based Electrochemiluminescence Biosensor for the Detection of Low-Density Lipoprotein by Increasing Sensitivity with Gold Nanoparticle Amplification

Mercaptoacetic acid (RSH)-capped CdS nanocrystals (NCs) was demonstrated to be electrochemically reduced during potential scan and react with the coreactant S2O82- to generate strong electrochemiluminescence (ECL) in aqueous solution. Based on the ECL of CdS NCs, a novel label-free ECL biosensor for the detection of low-density lipoprotein (LDL) has been developed by using self-assembly and gold nanoparticle amplification techniques. The biosensor was prepared as follows:  The gold nanoparticles were first assembled onto a cysteamine monolayer on the gold electrode surface. This gold nanoparticle-covered electrode was next treated with cysteine and then reacted with CdS NCs to afford a CdS NC-electrode. Finally, apoB-100 (ligand of LDL receptor) was covalently conjugated to the CdS NC-electrode. The modification procedure was characterized by cyclic voltammetry, electrochemical impedance spectroscopy, and atomic force microscopy, respectively. The resulting modified electrode was tested as ECL biosensor for LDL detection. The LDL concentration was measured through the decrease in ECL intensity resulting from the specific binding of LDL to apoB-100. The ECL peak intensity of the biosensor decreased linearly with LDL concentration in the range of 0.025−16 ng mL-1 with a detection limit of 0.006 ng mL-1. The CdS NCs not only showed high ECL intensity and good biocompatibility but also could provide more binding sites for apoB-100 loading. In addition, the gold nanoparticle amplification for protein ECL analysis was applied to the improvement of the detection sensitivity. Thus, the biosensor exhibited high sensitivity, good reproducibility, rapid response, and long-term stability

Versatile Photoelectrochemical Biosensing for Hg²⁺ and Aflatoxin B1 Based on Enhanced Photocurrent of AgInS₂ Quantum Dot–DNA Nanowires Sensitizing NPC–ZnO Nanopolyhedra

Eliminating false positives or negatives in analysis has been a challenge. Herein, a phenomenon of polarity-switching photocurrent of AgInS2 quantum dot (QD)–DNA nanowires reversing nitrogen-doped porous carbon–ZnO (NPC–ZnO) nanopolyhedra was found for the first time, and a versatile photoelectrochemical (PEC) biosensor with a reversed signal was innovatively proposed for dual-target detection. NPC–ZnO is a photoactive material with excellent PEC properties, while AgInS2 QDs as a photosensitive material match NPC–ZnO in the energy level, which not only promotes the transfer of photogenerated carriers but also switches the direction of PEC current. Furthermore, in order to prevent spontaneous agglomeration of AgInS2 (AIS) QDs and improve its utilization rate, a new multiple-branched DNA nanowire was specially designed to assemble AgInS2 QDs for constructing amplified signal probes, which not only greatly increased the load of AgInS2 QDs but also further enhanced the photoelectric signal. When the target Hg2+-induced cyclic amplification process generated abundant RDNA, the DNA nanowire signal probe with plenty of QDs was linked to the NPC–ZnO/electrode by RDNA, generating greatly amplified polarity-reversed photocurrent for signal “ON” detection of Hg2+. After specific binding of the target (aflatoxin B1, AFB1) to its aptamer, the signal probes of AIS QD-DNA nanowires were released, realizing signal “OFF” assay of AFB1. Thus, the proposed new PEC biosensor provides a versatile method for detection of dual targets and also effectively avoids both false positive and negative phenomena in the assay process, which has great practical application potential in both environmental and food analysis

Fluorescent Mn:ZnCdS@ZnS and CdTe Quantum Dots Probes on SiO₂ Microspheres for Versatile Detection of Carcinoembryonic Antigen and Monitoring T4 Polynucleotide Kinase Activity

Versatile fluorescent quantum dots (QDs) probes on SiO2 microspheres were prepared and used for detection of carcinoembryonic antigen (CEA) and monitoring T4 polynucleotide kinase (PNK) activity by integrating with amplification strategy. The highly fluorescent Mn:ZnCdS@ZnS and CdTe QDs showed different emission peaks. The amino-modified SiO2 microspheres with good morphology and no fluorescence interference were designed to link DNA and fabricate multiple branched QDs probes. First, CEA-induced target recycle amplification technique was combined with the Mn:ZnCdS@ZnS QDs labeled P2 signal probe for sensitive detection of CEA. Then, the formed DNA S1–DNA3 double strands further polymerized and proceeded exonuclease-cleavage reaction in the presence of T4 PNK, the released DNA fragments were used to trigger assembly of multibranched CdTe QDs-DNA signal probe (P1) by hybridization chain reaction (HCR), and achieved a greatly amplified fluorescence detection of PNK. The detection limits for CEA and PNK were 0.1 pg/mL and 0.001 U/mL, which was comparable to the reported methods. It is for the first time that the multiple branched QDs probes was coupled with HCR and cycling amplification strategy for versatile fluorescence detection of CEA and PNK activity. It shows great potential for early clinical diagnosis of cancer and the nucleotide kinase-target drug discovery

Electrochemiluminescence Immunosensor Based on CdSe Nanocomposites

A novel strategy for the enhancement of electrochemiluminescence (ECL) was developed by combining CdSe nanocrystals (NCs), carbon nanotube−chitosan (CNT−CHIT), and 3-aminopropyl-triethoxysilane (APS). A label-free ECL immunosensor for the sensitive detection of human IgG (HIgG) was fabricated. The colloidal solution containing CdSe NCs/CNT−CHIT composite was first covered on the Au electrode surface to form a robust film, which showed high ECL intensity and good biocompatibility. After APS as a cross-linker was covalently conjugated to the CdSe NCs/CNT−CHIT film, the ECL intensity was greatly enhanced. And, an intensity about 20-fold higher than that of the CdSe NCs/CNT−CHIT film was observed. After antibody was bound to the functionalized film via glutaric dialdehyde (GLD), the modified electrode could be used as an ECL immunosensor for the detection of HIgG. The specific immunoreaction between HIgG and antibody resulted in the decrease in ECL intensity. The ECL intensity decreased linearly with HIgG concentration in the range of 0.02−200 ng mL−1, and the detection limit was 0.001 ng mL−1. The immunosensor has the advantages of high sensitivity, speed, specificity, and stability and could become a promising technique for protein detection