A microchip electrophoresis-based fluorescence signal amplification strategy for highly sensitive detection of biomolecules

Aptamer-mediated double strand displacement amplification with microchip electrophoresis for ultrasensitive detection of Salmonella typhimurium

Rapid and quantitative detection of foodborne bacteria is of great significance to public health. In this work, an aptamer-mediated double strand displacement amplification (SDA) strategy was first explored to couple with microchip electrophoresis (MCE) for rapid and ultrasensitive detection of Salmonella typhimurium (S. Typhimurium). In double-SDA, a bacteria-identified probe consisting of the aptamer (Apt) and trigger sequence (Tr) was ingeniously designed. The aptamer showed high affinity to the S. Typhimurium, releasing the Tr sequence from the probe. The released Tr hybridized with template C1 chain, initiating the first SDA to produce numerous output strands (OS). The second SDA process was induced with the hybridization of the liberated OS and template C2 sequence, generating a large number of reporter strands (RS), which were separated and quantified through MCE. Cascade signal amplification and rapid separation of nucleic acids could be realized by the proposed double-SDA method with MCE, achieving the limit of detection for S. typhimurium down to 6 CFU/mL under the optimal conditions. Based on the elaborate design of the probes, the double-SDA assisted MCE strategy achieved better amplification performance, showing high separation efficiency and simple operation, which has satisfactory expectation for bacterial disease diagnosis.

Isothermal strand displacement polymerase reaction (ISDPR)-assisted microchip electrophoresis for highly sensitive detection of cancer associated microRNAs

More and more studies have found that microRNAs (miRNAs) are markers of cancer, and detection of miRNAs is beneficial for early diagnosis and prognosis of cancer. In this paper, the isothermal strand displacement polymerase reaction (ISDPR), which is an enzyme-assisted nucleic acid amplification method, was studied to combine with microchip electrophoresis (MCE) for a simultaneously detection of two cancer related miRNAs named microRNA-21 (miR-21) and microRNA-221 (miR-221). In the ISDPR amplification, two different DNA hairpins (HPs) were specifically designed, so that miR-21 and miR-221 could respectively bind to HPs and started ISDPR amplification to generate two different products which were ultimately detected by MCE. The optimal conditions of ISDPR were carefully investigated, and the limits of detection (LOD) of miR-21 and miR-221 were as low as 0.35 fM and 0.25 fM (S/N = 3) respectively under these conditions. The human lung tumor cells and serum samples were analyzed by this ISDPR-MCE method and satisfactory results were obtained, which means that this method is of high sensitivity, high efficiency, low reagent consumption and simple operation in miRNAs detection.

Cyclic Multiple Primer Generation Rolling Circle Amplification Assisted Capillary Electrophoresis for Simultaneous and Ultrasensitive Detection of Multiple Pathogenic Bacteria

Efficient, accurate, and economical detection of pathogenic bacteria is crucial in ensuring food safety and preventing foodborne illnesses. How to fulfill the highly sensitive and simultaneous detection of multiple trace pathogenic bacteria is a big challenge. In this work, capillary electrophoresis coupled with a cyclic multiple primer generation rolling circle amplification (cyclic MPG-RCA) was studied for highly sensitive and simultaneous detection of three kinds of pathogenic bacteria. The cyclic MPG-RCA was based on a carefully designed clover-shaped DNA probe, in which three "leaves" corresponded to three types of aimed pathogenic bacteria: Shigella dysenteriae (S. dysenteriae), Salmonella enterica subsp. enterica serovar Typhi (S. Typhi), and Vibrio parahaemolyticus (V. parahaemolyticus). Under the optimal experimental conditions, the limits of detection (S/N = 3) of this method for bacterial target DNA were 11.4 amol·L-1 (S. dysenteriae), 4.88 amol·L-1 (S. Typhi), and 14.9 amol·L-1 (V. parahaemolyticus), and the conversion concentrations for the target bacteria were 10 colony-forming units (CFU)·mL-1 (S. dysenteriae), 3 CFU·mL-1 (S. Typhi), and 12 CFU·mL-1 (V. parahaemolyticus). This method had been applied to the detection of tap water samples with good results, which proved that it could be used as an effective tool for trace pathogenic bacteria monitoring in foods, environments, and medicines.

Detection of Escherichia coli by capillary electrophoresis assisted by large volume sample stacking and nicking endonuclease signal amplification

Efficient, accurate and economical detection of pathogenic bacteria is crucial in ensuring food safety and preventing foodborne illnesses. In this study, a capillary electrophoresis coupled laser-induced fluorescence assay (CE-LIF) was developed for the detection of Escherichia coli (E. coli) by detecting its specific DNA. The CE-LIF was assisted by both online enrichment and offline amplification to improve the detection sensitivity of bacterial DNA. Here the online amplification was performed by large volume sample stacking (LVSS), while the offline amplification was nicking endonuclease signal amplification (NESA). Under the optimal experimental conditions, the detection limit of bacterial target DNA was 2.5 fM, and the conversion concentration of E. coli was 3 CFU · mL-1. The method had been applied to the detection of commercially available skim milk samples with good results, which proved that it could be used as an effective tool for food and environmental bacteria monitoring.

Ultrasensitive detection of exosomes by microchip electrophoresis combining with triple amplification strategies

The analysis of exosomes is significant as they can be used for various pathophysiological processes, especially cancer related intercellular communication. Therefore, a convenient, reliable, and sensitive detection method is urgently needed. Strand displacement amplification (SDA) and catalytic hairpin assembly (CHA) are two kinds of effective isothermal nucleic acid amplification methods. In this article, an efficient quantitative MCE method for detecting human breast cancer cell (MCF-7) exosomes assisted by triple amplification strategies combining cholesterol probe (Chol-probe) with SDA-CHA was first developed. CD63 aptamer was immobilized on the avidin magnetic beads to specifically capture exosomes and then Chol-probe with high affinity was spontaneously inserted into the exosome membrane, which was the first step of amplification strategy to improve detection sensitivity. After magnetic separation, Chol-probe could complement ssDNA and trigger SDA, producing a large number of DNA sequences (Ta) to trigger CHA, achieving SDA-CHA amplification. Under optimal conditions, the detection limit (LOD) for MCF-7 exosomes was as low as 26 particle/μL (S/N = 3). This method provides an effective approach for sensitive and accurate quantification of tumor exosomes, and can be expected to detect exosomes in clinical samples.

Biosensing bacterial 16S rDNA by microchip electrophoresis combined with a CRISPR system based on real-time crRNA/Cas12a formation

The accurate, simple and sensitive detection of bacterial infections at the early stage is highly valuable in preventing the spread of disease. Recently, CRISPR-Cas12a enzyme-derived nucleic acid detection methods have emerged along with the discovery of the indiscriminate single-stranded DNA (ssDNA) cleavage activity of Cas12a. These nucleic acid detection methods are made effective and sensitive by combining them with isothermal amplification technologies. However, most of the proposed CRISPR-Cas12a strategies involve Cas-crRNA complexes in the preassembled mode, which result in inevitable nonspecific background signals. Besides, the signal ssDNA used in these strategies needs tedious pre-labeling of the signal molecules. Herein, a post-assembly CRISPR-Cas12a method has been proposed based on target-induced transcription amplification and real-time crRNA generation for bacterial 16S rDNA biosensing. This strategy is label-free through the combination of microchip electrophoresis (MCE) detection. In addition, this method eliminates the need for a protospacer adjacent motif (PAM) on the target sequences, and has the potential to be an effective and simple method for nucleic acid detection and infectious disease diagnosis.

Fluorescence Aptasensor of Tuberculosis Interferon-γ in Clinical Samples Regulated by Steric Hindrance and Selective Identification

Although there are many interferon gamma (IFN-γ)-based tools for tuberculosis (TB) diagnosis, they are less sensitive and laborious. Here, we developed an IFN-γ aptasensor using pyrophosphate-cerium coordination polymeric nanoparticles (PPi-Ce CPNs) as signal reporters and a double-stranded DNA as a probe. The sensor was realized by sterically regulating the polymerization elongation of terminal deoxynucleotidyl transferase (TdT) and the selective recognition reaction of PPi-Ce CPNs. This method employs PPi-Ce CPNs to selectively identify Cu²⁺ and polyT-templated copper nanoparticles (Cu NPs), as well as a TdT-assisted amplification technique. Our data showed that under optimized experimental conditions, a limit of detection of as low as 0.25 fg/mL was achieved, with a linear range of 1-100 fg/mL, and a good target protein specificity. The detection sensitivity was an order of magnitude higher than that observed with Cu NPs when used as signal reporters. This IFN-γ quantification technique was further validated in clinical samples using 57 clinical TB patients (22 negative and 35 positive). Our findings agreed with those from enzyme-linked immunosorbent assay, GeneXpert MTB/rifampin assay, and polymerase chain reaction detection of TB-DNA and those from clinical imaging techniques. Therefore, our analytical system may provide an additional and more sensitive tool for the early diagnosis of TB.

Interferon-γ detection in point of care diagnostics: Short review

Interferon (IFN)-γ is a cytokine secreted by immune cells. The elevated levels of IFN-γ are an early indicator of multiple diseases such as tuberculosis and autoimmune diseases. This short review focuses on different sensing methods based on optical, electrochemical, and mechanical principles. We explain how specific biorecognition molecules such as antibodies and aptamers are employed in the sensing methods. We also compare different surface functionalization methods and their details. Although the review gives an overview of only IFN-γ sensing, the same strategies can be applied to sensing other analytes with appropriate modifications.

Recent Advances in Aptasensor for Cytokine Detection: A Review

Cytokines are proteins secreted by immune cells. They promote cell signal transduction and are involved in cell replication, death, and recovery. Cytokines are immune modulators, but their excessive secretion causes uncontrolled inflammation that attacks normal cells. Considering the properties of cytokines, monitoring the secretion of cytokines in vivo is of great value for medical and biological research. In this review, we offer a report on recent studies for cytokine detection, especially studies on aptasensors using aptamers. Aptamers are single strand nucleic acids that form a stable three-dimensional structure and have been receiving attention due to various characteristics such as simple production methods, low molecular weight, and ease of modification while performing a physiological role similar to antibodies.

Review of microchip analytical methods for the determination of pathogenic Escherichia coli

Bacterial infections remain the principal cause of mortality worldwide, making the detection of pathogenic bacteria highly important, especially Escherichia coli (E. coli). Current E. coli detection methods are labour-intensive, time-consuming, or require expensive instrumentation, making it critical to develop new strategies that are sensitive and specific. Microchips are an automated analytical technique used to analyse food based on their separation efficiency and low analyte consumption, which make them the preferred method to detect pathogenic bacteria. This review presents an overview of microchip-based analytical methods for analysing E. coli, which were published in recent years. Specifically, this review focuses on current research based on microchips for the detection of E. coli and reviews the limitations of microchip-based methods and future perspectives for the analysis of pathogenic bacteria.

A novel intracellular signal amplification strategy for the quantification of ATP in single cells by microchip electrophoresis with laser-induced fluorescence detection

An intracellular signal amplification strategy was developed for the quantification of ATP in single cells by microchip electrophoresis with laser-induced fluorescence detection. By using the method proposed, intracellular ATP levels in single HeLa, HepG2 and HL-7702 cells were found to be in the range of 30-150, 30-140, and 19-120 fmol per cell, respectively.

An ultrasensitive microchip electrophoresis chemiluminescence assay platform for detection of trace biomolecules

An ultrasensitive microchip electrophoresis chemiluminescence (MCE-CL) assay platform based on separation assisted cascade signal amplification was developed for detection of trace biomolecules. In this work, the aptamer was used as a target probe to bind target molecule and triggering cascade signal amplification reaction. The horseradish peroxide labeled DNA (HRP-DNA) was used as signal probe, utilizing nucleic acid hybridization and exonuclease cutting technology realized ultrasensitive detection of biomolecules on the MCE-CL assay platform. Taking gamma interferon (IFN-γ) as a model analyte, the linear range for IFN-γ detection is 8.0 × 10^-15-1.0 × 10^-8 M, the detection limit is 1.6 fM, which is six orders magnitude lower than that of without signal amplification. The proposed method was successfully applied for the quantification of IFN-γ in human plasma samples. It was demonstrated that the MCE-CL assay platform was quick, sensitive, and highly selective. It may serve as a tool for clinical analysis of IFN-γ to assist in the diagnosis of disease.

Netlike hybridization chain reaction assembly of DNA nanostructures enables exceptional signal amplification for sensing trace cytokines

The monitoring and detection of molecular biomarkers play crucial roles in disease diagnosis and treatment. In this work, we proposed a target-responsive netlike hybridization chain reaction (nHCR) DNA nanostructure construction method, which can offer an exceptional signal enhancement, for highly sensitive fluorescence detection of cytokine, interferon-gamma (IFN-γ). The presence of the target cytokine can lead to the conformational change of the aptamer recognition hairpin probes and the liberation of the nHCR initiator strands, which further trigger the nHCR process between two dye-labeled and double hairpin-structured probes to form netlike DNA nanostructures. The formation of the DNA nanostructures brings the dyes into close proximity, resulting in significantly amplified fluorescence resonance energy transfer signals for sensitive and enzyme-free detection of IFN-γ. The present method has a detection limit of 1.2 pM and a dynamic linear range of 5 to 1000 pM for IFN-γ detection. Besides, with the high specificity of the aptamer probe and the significant signal amplification of the nHCR, such an IFN-γ detection strategy shows excellent selectivity and high sensitivity, which can be potentially applied to detect IFN-γ in human serums. With such a demonstration of the detection of IFN-γ, this proposed method can be extended for detecting different types of biomolecules.

Multiplex detection of quality indicator molecule targets in urine using programmable hairpin probes based on a simple double-T type microchip electrophoresis platform and isothermal polymerase-catalyzed target recycling

Recently, it has been crucial to be able to detect and quantify small molecular targets simultaneously in biological samples. Herein, a simple and conventional double-T type microchip electrophoresis (MCE) based platform for the multiplex detection of quality indicator molecule targets in urine, using ampicillin (AMPI), adenosine triphosphate (ATP) and estradiol (E2) as models, was developed. Several programmable hairpin probes (PHPs) were designed for detecting different targets and triggering isothermal polymerase-catalyzed target recycling (IPCTR) for signal amplification. Based on the target-responsive aptamer structure of PHP (Domain I), target recognition can induce PHP conformational transition and produce extension duplex DNA (dsDNA), assisted by primers & Bst polymerase. Afterwards, the target can be displaced to react with another PHP and initiate the next cycle. After several rounds of reaction, the dsDNA can be produced in large amounts by IPCTR. Three targets can be simultaneously converted to dsDNA fragments with different lengths, which can be separated and detected using MCE. Thus, a simple double-T type MCE based platform was successfully built for the homogeneous detection of multiplex targets in one channel. Under optimal conditions, the assay exhibited high throughput (48 samples per hour at most, not including reaction time) and sensitivity to three targets in urine with a detection limit of 1 nM (ATP), 0.05 nM (AMPI) and 0.1 nM (E2) respectively. The multiplex assay was successfully employed for the above three targets in several urine samples and combined the advantages of the high specificity of programmable hairpin probes, the excellent signal amplification of IPCTR, and the high through-put of MCE which can be employed for screening in biochemical analysis.

A target-responsive liposome activated by catalytic hairpin assembly enables highly sensitive detection of tuberculosis-related cytokine

Here, we propose a new fluorescence method to detect tuberculosis-related cytokine by using a target-responsive liposome activated by catalytic hairpin assembly. The method combines a DNA self-assembly based amplification process with a liposome-based signal amplification process, therefore offering a very high sensitivity.

A decade of microchip electrophoresis for clinical diagnostics - A review of 2008-2017

A core element in clinical diagnostics is the data interpretation obtained through the analysis of patient samples. To obtain relevant and reliable information, a methodological approach of sample preparation, separation, and detection is required. Traditionally, these steps are performed independently and stepwise. Microchip capillary electrophoresis (MCE) can provide rapid and high-resolution separation with the capability to integrate a streamlined and complete diagnostic workflow suitable for the point-of-care setting. Whilst standard clinical diagnostics methods normally require hours to days to retrieve specific patient data, MCE can reduce the time to minutes, hastening the delivery of treatment options for the patients. This review covers the advances in MCE for disease detection from 2008 to 2017. Miniaturised diagnostic approaches that required an electrophoretic separation step prior to the detection of the biological samples are reviewed. In the two main sections, the discussion is focused on the technical set-up used to suit MCE for disease detection and on the strategies that have been applied to study various diseases. Throughout these discussions MCE is compared to other techniques to create context of the potential and challenges of MCE. A comprehensive table categorised based on the studied disease using MCE is provided. We also comment on future challenges that remain to be addressed.

Microfluidic electrophoretic non-enzymatic kanamycin assay making use of a stirring bar functionalized with gold-labeled aptamer, of a fluorescent DNA probe, and of signal amplification via hybridization chain reaction

The authors describe an enzyme-free aptamer-based assay for the determination of the model antibiotic kanamycin (Kana). The method is making use of (a) microfluidic chip electrophoresis; (b) a stirring bar carrying a gold-labeled aptamer probe, and (c) the hybridization chain reaction (HCR) for signal amplification. Firstly, a stirring bar (length: 1 cm; diameter: 0.2 mm) was modified with a large amount of duplex DNA and then hybridized with aptamer and its partially complementary chains (cDNA). In the presence of Kana, the binding between the Kana and aptamer unwinds the duplex structures and releases a corresponding amount of cDNA into the supernatant. The released cDNA triggers the HCR in the presence of H1 and H2 DNA hairpin to produce a large amount of duplex DNA chains with different lengths. At the same time, the amounts of H1 and H2 are reduced. The decreased signal of H1/H2 after several HCR cycles can be used to quantify kana in the 1 pg·mL^-1 to 10 ng·mL^-1, with a detection limit of 0.29 pg·mL^-1. The signal is generated by reading the fluorescence, best at excitation/emission maxima of 470/525 nm. The whole detection process takes 3 min only. The assay was employed to the detection of Kana in spiked milk and fish samples. Results are consistent with those of an enzyme linked immunosorbent assay. The assay has high throughput, high selectivity, and high amplification capability. Graphical abstract Schematic of a stirring bar functionalized with gold-labeled aptamer acting as the capture probe. It can capture the target and release primer simultaneously. The primer triggers the hybridization chain reaction inducing the consumption of H1 and H2. After a certain reaction time, the mixture is injected into the MCE platform for microfluidic electrophoretic separation and fluorometric detection.

An ultrasensitive microchip electrophoresis assay based on separation-assisted double cycling signal amplification strategy for microRNA detection in cell lysate

An ultrasensitive microchip electrophoresis assay was developed for microRNA detection.

Novel label-free and high-throughput microchip electrophoresis platform for multiplex antibiotic residues detection based on aptamer probes and target catalyzed hairpin assembly for signal amplification

Novel label-free and multiplex aptasensors have been developed for simultaneous detection of several antibiotics based on a microchip electrophoresis (MCE) platform and target catalyzed hairpin assembly (CHA) for signal amplification. Kanamycin (Kana) and oxytetracycline (OTC) were employed as models for testing the system. These aptasensors contained six DNA strands termed as Kana aptamer-catalysis strand (Kana apt-C), Kana inhibit strand (Kana inh), OTC aptamer-catalysis strand (OTC apt-C), OTC inhibit strand (OTC inh), hairpin structures H1 and H2 which were partially complementary. Upon the addition of Kana or OTC, the binding event of aptamer and target triggered the self-assembly between H1 and H2, resulting in the formation of many H1-H2 complexes. They could show strong signals which represented the concentration of Kana or OTC respectively in the MCE system. With the help of the well-designed and high-quality CHA amplification, the assay could yield 300-fold amplified signal comparing that from non-amplified system. Under optimal conditions, this assay exhibited a linear correlation in the ranges from 0.001ngmL^-1 to 10ngmL^-1, with the detection limits of 0.7pgmL^-1 and 0.9pgmL^-1 (S/N=3) toward Kana and OTC, respectively. The platform has the following advantages: firstly, the aptamer probes can be fabricated easily without labeling signal tags for MCE detection; Secondly, the targets can just react with probes and produce the amplified signal in one-pot. Finally, the targets can be simultaneously detected within 10min in different channels, thus high-throughput measurement can be achieved. Based on this work, it is estimated that this detection platform will be universally served as a simple, sensitive and portable platform for antibiotic contaminants detection in biological and environmental samples.

Highly effective molecule converting strategy based on enzyme-free dual recycling amplification for ultrasensitive electrochemical detection of ATP

An enzyme-free and highly effective molecule converting strategy was described for the sensitive electrochemical detection of ATP based on target-driven catalytic hairpin assembly and Mg²⁺-dependent DNAzymes.