Rational Fabrication of a Smart Electrochemiluminescent Sensor: Synergistic Effect of a Self-Luminous Faraday Cage and Biomimetic Magnetic Vesicles

Faraday cage-type self-powered immunosensor based on hybrid enzymatic biofuel cell

Self-powered immunosensors (SPIs) based on enzymatic biofuel cell (EBFC) have low sensitivity and poor stability due to the high impedance of the immune sandwich and the vulnerability of enzymes to environmental factors. Here, we applied the Faraday cage-type sensing mode on a hybrid biofuel cell (HBFC)-based SPI for the first time, which exhibited high sensitivity and stability. Cytokeratin 19 fragment (CYFRA 21-1) was used as a model analyte. Au nanoparticle-reduced graphene oxide (Au-rGO) composite was used as the supporting matrix for immunoprobe immobilized with detection antibody and glucose dehydrogenase (GDH), also the builder for Faraday cage structure on the bioanode in the presence of antigen. After the combination of immunoprobe, antigen, and the antibody on the bioanode, the Faraday cage was constructed in case the AuNP-rGO was applied as a conductive cage for electron transfer from GDH to the bioanode without passing through the poorly conductive protein. With the assistance of the Faraday cage structure, the impedance of the bioanode decreased significantly from 4000 to 300 Ω, representing a decline of over 90%. The sensitivity of the SPI, defined as the changes of open circuit voltage (OCV) per unit concentration of the CYFRA 21-1, was 68 mV [log (ng mL-1)]-1. In addition, Fe-N-C was used as an inorganic cathode material to replace enzyme for oxygen reduction reaction (ORR), which endowed the sensor with 4-week long-term stability. This work demonstrates a novel sensing platform with high sensitivity and stability, bringing the concept of hybrid biofuel cell-based self-powered sensor.

Ti3C2 and Ti2C MXene materials for high-performance isolation of extracellular vesicles via coprecipitation

Two-dimensional (2D) materials such as MXenes, are usually well utilized in the field of catalysts and battery due to their good hydrophilicity and diversified surface terminals. However, their potential applications in the treatment of biological samples have not been widely concerned. Extracellular vesicles (EVs) contain unique molecular signatures and could be used as biomarkers for the detection of severe diseases such as cancer, as well as monitoring the therapeutic response. In this work, two kinds of MXene materials (Ti₃C₂ and Ti₂C) were successfully synthesized and employed in the isolation of EVs from the biological samples by taking advantage of the affinity interaction between the titanium (Ti) in MXenes and the phospholipid membrane of EVs. Compared with Ti₂C MXene materials, TiO₂ beads and the other EVs isolation methods, Ti₃C₂ MXene materials exhibited excellent isolation performance via the coprecipitation with EVs due to the abundant unsaturated coordination of Ti²⁺/Ti³⁺, and the dosage of materials was the lowest. Meanwhile, the whole isolation process could be done within 30 min and integrated well with the following analysis of proteins and ribonucleic acids (RNAs), which was also convenient and economic. Furthermore, the Ti₃C₂ MXene materials were used to isolate the EVs from the blood plasma of colorectal cancer (CRC) patients and healthy donors. Proteomics analysis of EVs showed that 67 proteins were up-regulated, in which most of them were closely related to CRC progression. These findings indicate that the MXene material-based EVs isolation method via coprecipitation provides an efficient tool for early diagnosis of diseases.

Washing-free electrogenerated chemiluminescence magnetic microbiosensors based on target assistant proximity hybridization for multiple protein biomarkers

This work reports washing-free electrogenerated chemiluminescence (ECL) magnetic microbiosensors based on target assistant proximity hybridization (TAPH) for multiple protein biomarkers for the first time. As a principle-of-proof, alpha-fetoprotein (AFP) was chosen as a model analyte, and biotin-DNA1 bound streptavidin-coated magnetic microbeads (MMB@SA⋅biotin-DNA1) were designed as the universal capture MMB, while the corresponding two antibodies tagged with DNA2 or DNA3 were utilized as hybrid recognition probes, and ruthenium complex-tagged DNA4-10A was designed as a universal ECL signal probe. When the capture MMB was added into the mixture solution (containing the analyte, hybrid recognition probes, signal probe and tri-n-propylamine), biocomplexes were formed on the MMB. After the resulting MMB was efficiently brought to the surface of a magnetic glassy carbon electrode (MGCE), ECL measurement was performed without a washing step, resulting in an increase in the ECL intensity. A model for ECL measuring the second-order rate constants of hybridization reactions on MMB was derived. It was found that the rate constants for hybridization reactions on MMB in rotating mode are 1.6-fold higher than those in shaking mode, and a suitable DNA length of the signal probe can improve the signal-to-noise ratio. The washing-free ECL method was developed for the determination of AFP with a much lower detection limit (LOD) of 0.04 ng mL^-1. The developed flexible strategy has been extended to determine D-dimer with an LOD of 0.1 ng mL^-1 and myoglobinglobin with an LOD of 1.1 ng mL^-1. This work demonstrated that the proposed strategy of ECL TAPH on MMB at MGCE is a washing-free and flexible promising strategy, and can be extended to qualify other multiple protein biomarkers in real clinical assays.

Performance enhancement of electrochemiluminescence magnetic microbiosensors by using double magnetic field actuation for cancer biomarkers and exosomes

This work reports the performance enhancement strategies on magnetic beads (MBs)-based electrochemiluminescence (ECL) platforms by using double magnetic field actuation of the ECL magnetic microbiosensors (MMbiosensors) for highly sensitive determination of cancer biomarker and exosomes. To obtain the high sensitivity and reproducibility of the ECL MMbiosensors, a series of strategies have been developed including replacing a conventional photomultiplier tube (PMT) with a diamagnetic PMT, replacing the stacked ring-disc magnets with circular-disc magnets lain-in glassy carbon electrode, adding a pre-concentration process of MBs using external magnet actuation. For fundamental research, the ECL MBs taken as the substitute of ECL MMbiosensors were prepared by binding biotinylated DNA tagged with Ru(bpy)₃²⁺ derivative (Ru1) to streptavidin-coated MB(MB@SA) were which showed that the developed strategies can enhance 45-fold sensitivity. Importantly, the developed MBs-based ECL platform was estimated by determination of prostate specific antigen (PSA) and exosomes. For PSA, MB@SA•biotin-Ab1(PSA) was taken as the capture probe and Ru1-labeled Ab2 (PSA) was done as ECL probe, while for exosomes, MB@SA•biotin-aptamer (CD63) was taken as the capture probe and Ru1-labeled Ab (CD9) was done as the ECL probe. The experiment results showed that the developed strategies can enhance 33-fold sensitivity of ECL MMbiosensors for PSA and exosomes. The detection limit is 0.28 ng mL^-1 for PSA and 4.9 × 102 particle mL-1 for exosomes. This work demonstrated that a series of proposed magnetic field actuation strategies greatly increase the sensitivity of the ECL MMbiosensors. The developed strategies can be expanded to MBs-based ECL and electrochemical biosensors for clinical analysis with greater sensitivity.

Liposome-assisted chemical redox cycling strategy for advanced signal amplification: A proof-of-concept toward sensitive electrochemiluminescence immunoassay

This work presents a novel signal amplification strategy for electrochemiluminescence (ECL) biosensor based on liposome-assisted chemical redox cycling for in situ formation of Au nanoparticles (Au NPs) on TiO₂ nanotubes (TiO₂ NTs) electrode. The system was exemplified by ascorbic acid (AA)-loaded liposome, the redox cycling of AA utilizing tris (2-carboxyethyl) phosphine (TCEP) as reductant, and the use of Au nanoclusters (Au NCs)/TiO₂ NTs as working electrode to implement the ECL detection of prostate specific antigen (PSA). Specifically, the AA-loaded liposomes were used as tags to label the captured PSA through a sandwich immunoreaction. After the lysate of the liposome was transferred onto the interface of Au NCs/TiO₂ NTs in the presence of Au³⁺ and TECP, the chemical redox cycling was triggered. In the cycling, Au³⁺ was directly reduced in situ by AA to form Au NPs on Au NCs/TiO₂ NTs electrode, whereas the oxidation product of AA was reduced by TCEP to regenerate AA. The large loading capacity of the liposome and chemical redox cycling resulted in the incomplete reduction of the Au NCs to Au NPs on the TiO₂ NTs electrode, enhancing the ECL intensity greatly. The multiple signal amplification strategy achieved an ultrasensitive detection for PSA with a detection limit down to 6.7 × 10^-15 g mL^-1 and a wide linear concentration range from 1.0 × 10^-14 to 1.0 × 10^-8 g mL^-1. It is believed that this work is anticipated to extend the employment of advanced chemical redox cycling reaction in the field of ECL bioassays.

MXenes Quantum Dots for Biomedical Applications: Recent Advances and Challenges

MXenes have aroused widespread interest in the biomedical field owing to their remarkable photo-thermal conversion capabilities combined with large specific surface areas. MXenes quantum dots (MQDs) have been synthesized either by the physical or chemical methods based on MXenes as precursors, which possess smaller size, higher photoluminescence, coupled with low cytotoxicity and many beneficial properties of MXenes, thereby having potential biomedical applications. Given this, this review summarized the synthesis methods, optical, surface and biological properties of MQDs along with their practical applications in the field of biomedicine. Finally, the authors make an outlook towards the synthesis, properties and applications of MQDs in the future biomedicine field.

Label- and enzyme-free plasmon-enhanced single molecule fluorescence detection of HIV DNA fragments based on a catalytic hairpin assembly

We developed a label- and enzyme-free single molecule fluorescence counting strategy for HIV DNA fragments detection. The nucleic acid biosensor consists of a 5' terminal connected with a triangular gold nanoplate, 3' terminal rich in guanine hairpin probe (HP1) and a hairpin probe HP2 complementary to the partial sequence of HP1. Without the existence of the target DNA, the DNA fragment rich in the guanine region is locked in a hairpin structure and cannot form a G-quadruplex, hence NMM exhibits a low fluorescence signal. When the target DNA exists, the hairpin assembly will trigger a strand displacement amplification reaction that produces a great number of G-quadruplexes, and the fluorescence brightness of NMM will be enhanced. The plasmon resonance effect of the triangular gold nanoplates will further amplify the fluorescence signal. This method can analyze the target DNA with high sensitivity and selectivity, and the detection limit is 0.83 fM. The analysis of the HIV DNA fragments in diluted human serum samples was successfully achieved, and the recovery rate was 92%-104%. Because of its easy operation and low cost, it has broad development potential in biochemical analysis and clinical applications.

Electrochemiluminescence Immunoassay Platform with Immunoglobulin G-Encapsulated Gold Nanoclusters as a "Two-In-One" Probe

Biomolecule-functionalized Au nanoclusters (AuNCs) have drawn great interest in the electrochemiluminescence (ECL) field due to their unique optical/electrical properties, biocompatibility, and versatile bioapplication potentials. Herein, we proposed a two-in-one ECL probe of immunoglobulin G-encapsulated AuNCs (IgG-AuNCs) for the development of a high-performance ECL immunoassay (ECLIA) platform. The IgG-AuNCs were not only used as an ECL probe due to their excellent anodic ECL performance with triethylamine (TEA) as a coreactant but also used as the biorecognition element because of their well-retained bioactivity of the IgG. As a proof of concept, a new type of competitive immunosensing platform has been applied to detect IgG representing several merits of facile preparation, rapid detection, sample saving, and good analytical performance. The sensing platform exhibited a linear range of 0.5-50,000 ng/mL with a limit of detection of 0.06 ng/mL for IgG detection with high selectivity. In addition, this convenient ECLIA platform also performed well in real serum sample detection. Notably, our work not only proved the "two-in-one" immuno-AuNC probe-based ECLIA strategy but also developed a rational framework for study of ECL bioassay platforms based on multifunctional AuNCs and other related nanomaterials.

Electrochemiluminescent immunoassay for the determination of CA15-3 and CA72-4 using graphene oxide nanocomposite modified with CdSe quantum dots and Ru(bpy)3 complex

A novel immunoassay is introduced based on co-reactant enhancing strategy for the electrochemiluminescent (ECL) determination of CA15-3 and CA72-4 tumor markers in real samples. For the preparation of the signaling probe, CA15-3 and CA72-4 antibodies first were labeled using Ru(bpy)₃²⁺-N-hydroxysuccinimide ester (Ru(bpy)₃²⁺-NHS) and conjugated with L-cysteine capped cadmium selenide (CdSe) quantum dots. Finally, it was cross-linked with chitosan-grafted graphene oxide (GO@CS) nanocomposite. The capture probe was constructed by deposition of multi-walled carbon nanotubes (MWCNT) at the surface of dual-working gold screen-printed electrodes (MWCNT-dwSPE) and covalent attachment of capture CA15-3 and CA72-4 antibodies to MWCNT-dwSPE. ECL signals were recorded by applying cyclic potential ranging from 0.3 to 1.1 V (vs. pseudo-reference Ag/AgCl) at the scan rate of 100 mV.s^-1. This immunoassay was used for determination of CA15-3 and CA72-4 in real samples the detection limits of 9.2 μU.ml^-1 and 89 μU.ml^-1 within linear ranges of 10 μU.ml^-1-500 U.ml^-1 and 100 μU.ml^-1-150 U.ml^-1, respectively. This immunoassay also showed acceptable accuracy with recoveries in the range 96.5-108 % and high reproducibility with RSD of 3.1 and 4.9.