Temperature-responsive split aptamers coupled with polymerase chain reaction for label-free and sensitive detection of cancer cells

Electrochemiluminescence resonance energy transfer biosensing platform between g-C3N4 nanosheet and Ru-SiO2@FA for dual-wavelength ratiometric detection of SARS-CoV-2 RdRp gene

Rational detection of syndrome coronavirus 2 (SARS-CoV-2) is crucial to prevention, control, and treatment of disease. Herein, a dual-wavelength ratiometric electrochemiluminescence (ECL) biosensor based on resonance energy transfer (RET) between g-C₃N₄ nanosheets and Ru-SiO₂@folic acid (FA) nanomaterials was designed to realize ultrasensitive detection of SARS-CoV-2 virus (RdRp gene). Firstly, the unique g-C₃N₄ nanosheets displayed very intense and stable ECL at 460 nm, then the triple helix DNA was stably and vertically bound to g-C₃N₄ on electrode by high binding affinity between ssDNA and g-C₃N₄. Meanwhile, trace amounts of target genes were converted to a large number of output by three-dimensional (3D) DNA walker multiple amplification, and the output bridged a multifunctional probe Ru-SiO₂@FA to electrode. Ru-SiO₂@FA not only showed high ECL at 620 nm, but also effectively quenched g-C₃N₄ ECL. As a result, ECL decreased at 460 nm and increased at 620 nm, which was used to design a rational ECL biosensor for detection of SARS gene. The results show that the biosensor has excellent detection sensitivity for RdRp gene with a dynamic detection range of 1 fM to 10 nM and a limit of detection (LOD) of 0.18 fM. The dual-wavelength ratio ECL biosensor has inestimable value and application prospects in the fields of biosensing and clinical diagnosis.

Antifouling Electrochemical Biosensor Based on the Designed Functional Peptide and the Electrodeposited Conducting Polymer for CTC Analysis in Human Blood

Circulating tumor cells (CTCs) are considered reliable cancer biomarkers for the liquid biopsy of many types of tumors. The direct detection of CTCs in human blood with normal biosensors, however, remains challenging because of severe biofouling in blood that contains various proteins and a large number of cells. Herein, we report the construction of an antifouling electrochemical biosensor capable of assaying CTCs directly in blood, based on a designed multifunctional peptide and the electrodeposited conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT). The designed peptide possesses antifouling capability in complex biological media and specific recognition ability to capture breast cancer cells MCF-7. Meanwhile, electrodeposited PEDOT can promote electron transfer at the sensing interface, improve the signal-to-noise ratio for the detection, and thus enhance the sensitivity of the biosensor. The integration of the multifunctional peptide and conducting polymer PEDOT ensures that the developed biosensor is able to perform directly in blood samples without purification or separation. The antifouling electrochemical biosensor for the detection of MCF-7 cells exhibits a wide linear range over 4 orders, with a limit of detection (LOD) of 17 cells mL^-1. More interestingly, even when performing in 25% human blood, the biosensor still retains a linear response with an LOD of 22 cells mL^-1, without suffering significantly from biofouling in real blood. This work provides a promising strategy for the direct analysis of CTCs in human blood without a complicated pretreatment, and it may find practical application in the liquid biopsy of cancers.

Xeno nucleic acid probes mediated methylation-specific PCR for single-base resolution analysis of N6-methyladenosine in RNAs

Reliable and cost-effective quantification of RNA modifications at a specific gene locus is essential to elucidate the pathogenic mechanism encoded by RNA epigenetics. Current methods to quantify N⁶-methyladenosine (m6A) at specific sites can hardly satisfy the requirement of clinical application because epigenetic information is easily lost through polymerase chain reaction (PCR) assay or other isothermal amplification methods unless tedious pretreatment is applied. Herein, we propose a simple xeno nucleic acid (XNA) as a blocker probe to mediate the methylation specific reverse transcription quantitative polymerase chain reaction (MsRT-qPCR) assay to directly magnify the minor differences between epigenetic bases and unmodified bases in RNA. Strand displacement reactions selectively initiated between the reverse transcription primer (RT-primer) and the XNA probe at the m6A template given the affinity differences between the blocker probes and the m6A-modified RNA (m6A-RNA) and unmodified RNA (A-RNA). Thus, preferential amplification of m6A-RNA was allowed. Integration of a well-established oligo-modified Fe₃O₄@UiO-66-NH₄ allowed purification of mRNA and lncRNA from cellular total RNA samples and greatly reduced the non-specific interference of m6A detection in real samples. Multiple specific sites of m6A in mRNA and lncRNA samples are also successfully quantified. The XNA probe-based m6A assay required only common and available lab equipment and materials, which can be applied in m6A-related fundamental studies and clinical diagnosis.

Ultra-sensitive and high efficiency detection of multiple non-small cell lung cancer-related miRNAs on a single test line in catalytic hairpin assembly-based SERS-LFA strip

Accurate quantification of multiple miRNAs biomarkers in body fluid is still a challenge for early screening of cancer. Herein, by catalytic hairpin assembly as a signal amplification strategy, we designed a novel surface-enhanced Raman scattering (SERS)-lateral flow assay (LFA) strip for ultrasensitive detection of miR-21 and miR-196a-5p in non-small cell lung cancer (NSCLC) urine on a single test (T) line. 4-mercaptobenzoic acid or 5,5'-dithiobis-2-nitrobenzoic acid as Raman molecules was labeled and two hairpin DNA sequence was modified gold nanocages (GNCs) were designed as two SERS tags. Through target miRNA-triggered catalytic hairpin assembly (CHA), the double-stranded DNAs (H1-H2 complex) formed by SERS tags and the related hairpin-structured DNA sequence 2 (H2) were immobilized on a single T line of SERS-LFA strip. This generated abundant "hot spots" because of the formation of numerous H1-H2 complex thus facilitated the SERS measurement. Through this method, two kinds of miRNAs were analyzed, resulting in limits of detection of 2.08 pM and 3.31 pM for miR-21 in PBS buffer and human urine, 1.77 pM and 2.18 pM for miR-196a-5p in PBS buffer and human urine. Significantly, the SERS-LFA strip exhibited high specificity and good repeatability toward miRNAs. The whole detection time was only 30 min, which means that the high detection efficiency of the strip. The clinical feasibility of the proposed method was also evaluated by detecting the levels of miR-21 and miR-196a-5p in urine samples from NSCLC patients and healthy subjects. The developed SERS-LFA strip has wide application prospect in biomedical research, drug development and early clinical diagnosis.

Prognostic prospect of soluble programmed cell death ligand-1 in cancer management

Aggressive tissue biopsy is commonly unavoidable in the management of most suspected tumor cases to conclusively verify the presence of cancerous cells through histological assessment. The extracted tissue is also immunostained for detection of antigens (tissue tumor markers) of potential prognostic or therapeutic importance to assist in treatment decision. Although liquid biopsies can be a powerful tool for monitoring treatment response, they are still excluded from standard cancer diagnostics, and their utility is still being debated in the scientific community. With a myriad of soluble tissue tumor markers now being discovered, liquid biopsies could completely change the current paradigms of cancer management. Recently, soluble programmed cell death ligand-1 (sPD-L1), which is found in the peripheral blood, i.e. serum and plasma, has shown potential as a pre-therapeutic predictive marker as well as a prognostic biomarker to monitor treatment efficacy. Thus, this review focuses on the emergence of sPD-L1 and promising technologies for its detection in order to support liquid biopsies for future cancer management.

A facile and label-free electrochemical aptasensor for tumour-derived extracellular vesicle detection based on the target-induced proximity hybridization of split aptamers

Facile detection of tumour-derived extracellular vesicles (EVs) is crucial to cancer diagnosis. Herein, a facile and label-free electrochemical aptasensor was fabricated to detect tumour-derived EVs based on the target-induced proximity hybridization of split aptamers. In this assay, two designed oligonucleotide probes containing fragments of a protein tyrosine kinase-7 (PTK7) aptamer were used to recognize and capture EVs containing PTK7. In the presence of target EVs, the aptamer-target ternary complex could induce proximity hybridization and form a DNA duplex on the electrode. The DNA duplex could bind more electroactive Ru(NH3)63+ through electrostatic attraction, resulting in an increased cathodic current signal. By virtue of the excellent electrochemical signal reporter RuHex, the specificity of the aptamer and proximity ligation, a facile EV electrochemical aptasensor with a detection limit of 6.607 × 105 particles per mL was realized. Furthermore, this aptasensor showed good selectivity to distinguish different tumour-derived EVs and was applied to detect EVs in complex biological samples. The proposed electrochemical aptasensor can be further extended to the detection of other EVs, thus showing great potential in clinical diagnosis.

Novel Luminescent Nanostructured Coordination Polymer: Facile Fabrication and Application in Electrochemiluminescence Biosensor for microRNA-141 Detection

A series of novel luminescent nanostructured coordination polymers (Ce-Ru-NCPs) with tunable morphologies have been successfully synthesized on a large scale at room temperature by a facile and rapid solution-phase method using Ce³⁺ and tris(4,4'-dicarboxylicacid-2,2'-bipyridyl) ruthenium(II) dichloride (Ru(dcbpy)₃²⁺). Among them, the flowerlike Ce-Ru-NCP shows good cathodic electrochemiluminescence (ECL) characteristics. The ECL efficiency of the Ce-Ru-NCP/S₂O₈^2- system is about 2.34 times that of the classic tris(2,2'-bipyridyl) ruthenium(II) dichloride/S₂O₈^2- (Ru(bpy)₃²⁺/S₂O₈^2-) system. Hence, we report a sensitive ECL biosensor for microRNA-141 (miRNA-141) detection based on the flowerlike Ce-Ru-NCP as a cathodic ECL luminophore and a bipedal three-dimensional (3D) DNA walking machine as a signal amplifier. Through the bipedal 3D DNA walking machine, trace targets can be converted to substantial secondary targets (marked with the quencher dopamine), and a significant quenching effect on the ECL signal is achieved. As a result, the proposed biosensor exhibits a relatively good sensitivity for miRNA-141 detection and shows a dynamic range from 1.0 × 10^-16 to 1.0 × 10^-6 mol·L^-1 with a limit of detection (LOD) of 33 amol·L^-1 (S/N = 3). The Ce-Ru-NCP with tunable morphologies and high ECL efficiency, intensity, and stability possesses potential applications in ECL analysis.

Recognition-Driven Remodeling of Dual-Split Aptamer Triggering In Situ Hybridization Chain Reaction for Activatable and Autonomous Identification of Cancer Cells

Proximity-dependent hybridization chain reaction (HCR) has shown great potential in sensing biomolecules on the cell surface. However, the requirement of two adjacent bioevents occurring simultaneously limits its application. To solve the problem, split aptamers with target binding ability were introduced to combine with split triggers for initiating HCR, thus producing a novel dual-split aptamer probe (DSAP). By employing cancer-related receptors as models, in situ HCR on a cancer cell surface induced by recognition-driven remodeling of the DSAP was demonstrated. The DSAP consisted of two sequences. Each contained two segments; one derived from split aptamers and the other originated in split triggers. In the presence of target cells, split aptamers reassembled on the cell surface under the "induced-fit effect", thus forcing two split triggers close to each other. The remodeled DSAP worked as an intact trigger, which opened the H1 hairpin probe and then hybridized with the H2 hairpin probe, thus initiating HCR to produce an activated fluorescence signal. As a proof of concept, human liver cancer SMMC-7721 cells and their split ZY11 aptamer were used to construct the DSAP. Results indicated that the DSAP realized sensitive analysis of target cells, permitting the actual detection of 20 cells in the buffer. Moreover, the specific identification of target cells in mixed cell samples and the quantitative analysis of target cells in serum were also achieved. The DSAP strategy is facile and universal, which not only would expand the application range of HCR but also might be developed as a multitarget detection technique for bioanalysis.

A light-up fluorescence assay for tumor cell detection based on bifunctional split aptamers

Light-up aptamers have attracted growing attention due to their advantages of being label-free and having low fluorescence background. In this work, we developed a light-up fluorescence assay for label-free detection of tumor cells based on a bifunctional split aptamer (BFSA) that contained two DNA strands (BFSA-a and BFSA-b). BFSA-a and BFSA-b were constructed by combining aptamers ZY11 and ThT.2-2, which could specifically bind to the tumor cell SMMC-7721 and activate the fluorescence of thioflavin T (ThT). A Helper strand was introduced to hybridize with BFSA-b, and then BFSA-a and BFSA-b were separated if the target cell was absent. Only when the target cell is present can BFSA-a approach and hybridize with BFSA-b due to the 'induced-fit effect', which made the Helper strand dissociate. Then ThT bound to BFSA and the fluorescence of ThT was activated. The results indicated that this fluorescence assay had a good linear response to the target cells in the range of 250-20 000 cells in 100 μL binding buffer; the lowest cell number actually detected was 125 cells in 100 μL buffer. This assay also displayed excellent selectivity and was successfully applied to detect target cells in 20% human serum samples. The design of bifunctional split aptamers realized no-washing, label-free, low-cost, one-step detection of tumor cells, which could generate detectable fluorescence signals just by mixing nucleic acid aptamers and fluorescent reporter molecules with target cells. Such a design of aptamer probes also has the potential to construct stimuli-responsive controlled drug delivery systems.

A Facile, Label-Free, and Universal Biosensor Platform Based on Target-Induced Graphene Oxide Constrained DNA Dissociation Coupling with Improved Strand Displacement Amplification

In this work, we report a low-cost and easy operation biosensor platform capable of detection of various analytes with high sensitivity and good selectivity. By ingeniously assigning the specific aptamer into a primer-template integrated DNA template, and using monolayer graphene oxide as a reversible and nonspecific inhibitor, the simple biosensor platform is set up. Without a target, the DNA template is constrained by the graphene oxide sheet and results in low signal. In the presence of a target, the constrained DNA template is released from the graphene oxide surface via a target-induced aptamer conformational change, and further amplified through the improved strand displacement amplification reaction. Therefore, the target detection is simply converted to DNA detection, and a correlation between target concentration and fluorescence signal can be set up. As a result, dozens-fold signal enhancement, high sensitivity, good selectivity, and potential practicability are achieved in target detection. More importantly, the proposed biosensor platform is versatile, meaning that it can greatly facilitate the detection of a variety of analytes. Due to the low cost and easy availability of sensing materials, and the elimination of tedious detection operations, we believe that this simple and universal biosensor platform can find wide applications in biological assay and environment monitoring.

Near-Infrared Fluorescent Ag2S Nanodot-Based Signal Amplification for Efficient Detection of Circulating Tumor Cells

The level of circulating tumor cells (CTCs) plays a critical role in tumor metastasis and personalized therapy, but it is challenging for highly efficient capture and detection of CTCs because of the extremely low concentration in peripheral blood. Herein, we report near-infrared fluorescent Ag₂S nanodot-based signal amplification combing with immune-magnetic spheres (IMNs) for highly efficient magnetic capture and ultrasensitive fluorescence labeling of CTCs. The near-infrared fluorescent Ag₂S nanoprobe has been successfully constructed through hybridization chain reactions using aptamer-modified Ag₂S nanodots, which can extremely improve the imaging sensitivity and reduce background signal of blood samples. Moreover, the antiepithelial-cell-adhesion-molecule (EpCAM) antibody-labeled magnetic nanospheres have been used for highly capture rare tumor cells in whole blood. The near-infrared nanoprobe with signal amplification and IMNs platform exhibits excellent performance in efficient capture and detection of CTCs, which shows great potential in cancer diagnostics and therapeutics.

An ultrasensitive electrochemiluminescence biosensor for multiple detection of microRNAs based on a novel dual circuit catalyzed hairpin assembly

A novel double-hairpin DNA inducing a dual circuit catalyzed hairpin assembly (DC-CHA) strategy was proposed to fabricate electrochemiluminescence (ECL) biosensors for multiple target (microRNA-21 and microRNA-155) ultrasensitive detection.

Dean flow assisted cell ordering system for lipid profiling in single-cells using mass spectrometry

A Dean flow assisted ordering system connected to an ESI-MS to identify single-cells in a subpopulation by lipid profiling.