Distance-based quantification of miRNA-21 by the coffee-ring effect using paper devices

Self-assembly of hyperbranched DNA network structure for signal amplification detection of miRNA

Catalytic hairpin assembly (CHA) and hybridization chain reaction (HCR) can achieve the high sensitivity and rapid reaction rate in detecting miRNA. However, the amplification efficiency by these methods are limited. Herein, an enzyme-free and label-free hyperbranched DNA network structure (HDNS) was designed, in which localized catalytic hairpin assembly (LCHA) and hybridization chain reaction occurred in the horizontal axis and longitudinal axis, respectively, exhibiting intensive signal dual-amplification. miRNA-122 was selected as the target on behalf of miRNA to design the HDNS sensor. The fluorescence signal change of HDNS showed good linearity for detecting miRNA-122 in the concentration range from 0.1 nM to 60 nM with a limit of detection (LOD) at 37 pM which was lower than those of the sensors based on separate CHA or HCR. Afterwards, the HDNS sensor was applied to detect miRNA-122 in serum samples with the recovery rate in the range of 97.2 %-107 %. The sensor could distinguish different kinds of miRNAs, even the family members with high sequence homology, exhibiting excellent selectivity. This method provided a novel design strategy for improving the sensitivity and selectivity of DNA sensor for miRNA detection.

Recent Developments in Paper-Based Sensors with Instrument-Free Signal Readout Technologies (2020-2023)

Signal readout technologies that do not require any instrument are essential for improving the convenience and availability of paper-based sensors. Thanks to the remarkable progress in material science and nanotechnology, paper-based sensors with instrument-free signal readout have been developed for multiple purposes, such as biomedical detection, environmental pollutant tracking, and food analysis. In this review, the developments in instrument-free signal readout technologies for paper-based sensors from 2020 to 2023 are summarized. The instrument-free signal readout technologies, such as distance-based signal readout technology, counting-based signal readout technology, text-based signal readout technology, as well as other transduction technologies, are briefly introduced, respectively. On the other hand, the applications of paper-based sensors with instrument-free signal readout technologies are summarized, including biomedical analysis, environmental analysis, food analysis, and other applications. Finally, the potential and difficulties associated with the advancement of paper-based sensors without instruments are discussed.

Distance-Based Self-Powered Signal Transduction of Ion-Selective Electrodes to an Electronic Paper Display Array

In this article, we report on the first distance-based readout self-powered potentiometric sensor. The approach is considered more user-friendly for detection by the naked eye and is less prone to optical interferences compared with a direct observation of the pixel darkening. pH-selective electrodes were chosen as a model system to demonstrate the principle in which seven bar-shaped pixels connected in series on one e-paper share one common ground. By connecting each of the pixels serially to capacitors of different capacitances, the fraction of the measurement cell voltage loaded onto the pixels becomes controllable. Consequently, the pixels give different gray values when powered by the same ion-selective electrode (ISE). As a result, the pH information on the sample is visualized as a distance-based signal and the dependence between the capacitance and 1/K (the reciprocal slope in the relationship between absorbance and pH) was constructed. In the current system, a 1 μF capacitance difference changes the value of 1/K by 4.18. With the current setup, the pH accuracy is about 0.5 when comparing the e-paper output to a color card.

Advances in Point-of-Care Testing of microRNAs Based on Portable Instruments and Visual Detection

MicroRNAs (miRNAs) are a class of small noncoding RNAs that are approximately 22 nt in length and regulate gene expression post-transcriptionally. miRNAs play a vital role in both physiological and pathological processes and are regarded as promising biomarkers for cancer, cardiovascular diseases, neurodegenerative diseases, and so on. Accurate detection of miRNA expression level in clinical samples is important for miRNA-guided diagnostics. However, the common miRNA detection approaches like RNA sequencing, qRT-PCR, and miRNA microarray are performed in a professional laboratory with complex intermediate steps and are time-consuming and costly, challenging the miRNA-guided diagnostics. Hence, sensitive, highly specific, rapid, and easy-to-use detection of miRNAs is crucial for clinical diagnosis based on miRNAs. With the advantages of being specific, sensitive, efficient, cost-saving, and easy to operate, point-of-care testing (POCT) has been widely used in the detection of miRNAs. For the first time, we mainly focus on summarizing the research progress in POCT of miRNAs based on portable instruments and visual readout methods. As widely available pocket-size portable instruments and visual detection play important roles in POCT, we provide an all-sided discussion of the principles of these methods and their main limitations and challenges, in order to provide a guide for the development of more accurate, specific, and sensitive POCT methods for miRNA detection.

An overview of biochemical technologies for the cancer biomarker miR-21 detection

In recent years, the incidence of cancer has continuously increased, in which various miRNAs have been proposed as biomarkers for the early screening of cancer patients. As a consequence, the development of accurate methods for miRNA quantification has become a major research challenge worldwide. As one of the first discovered oncogenic miRNAs, microRNA-21 (miR-21) has been highlighted for its critical role in cancers. This review describes the main techniques currently available for miR-21 detection, compares the differences of the methods and the amplification strategies, and provides an overview of the state of knowledge in the field.

The Road to Unconventional Detections: Paper-Based Microfluidic Chips

Conventional detectors are mostly made up of complicated structures that are hard to use. A paper-based microfluidic chip, however, combines the advantages of being small, efficient, easy to process, and environmentally friendly. The paper-based microfluidic chips for biomedical applications focus on efficiency, accuracy, integration, and innovation. Therefore, continuous progress is observed in the transition from single-channel detection to multi-channel detection and in the shift from qualitative detection to quantitative detection. These developments improved the efficiency and accuracy of single-cell substance detection. Paper-based microfluidic chips can provide insight into a variety of fields, including biomedicine and other related fields. This review looks at how paper-based microfluidic chips are prepared, analyzed, and used to help with both biomedical development and functional integration, ideally at the same time.

Recent advances of catalytic hairpin assembly and its application in bioimaging and biomedicine

Catalytic hairpin assembly (CHA) appears to be a particularly appealing nucleic acid circuit because of its powerful amplification capability, simple protocols, and enzyme-free and isothermal conditions, and can combine with various signal output modes for the biosensing of various analytes. Especially in the last five years, vast CHA related studies have sprung up. With the deep exploration of the CHA mechanism, some novel and excellent CHA strategies have been proposed; meanwhile the CHA cascade strategies with various amplification techniques further improve the analysis performance. Furthermore, diverse CHA based biosensors have been tactfully engineered and extensively employed in imaging applications in living cells and in vivo ascribed to its gentle reaction, efficient amplification and universality. Hence, we present a comprehensive and systematic summary of the progress in CHA and its application in bioimaging and biomedicine to date. At first, we introduced the mechanism and diversification of CHA in detail, including the newly developed CHA and its ingenious combination with a variety of other technologies. Concurrently, we summarized the latest application progress of different CHA strategies in bioimaging and biomedicine, highlighting the merits and drawbacks of representative approaches. Finally, we put forward some views on the challenges and prospects of CHA in bioimaging and biomedicine in the future.

DNAzyme-controlled plasmonic coupling for SERS-based determination of Salmonella typhimurium using hybridization chain reaction self-assembled G-quadruplex

A facile and rapid SERS strategy for S. typhimurium detection based on hybridization chain reaction (HCR) self-assembled G-quadruplex DNAzyme (GQH DNAzyme)-controlled plasmonic coupling was developed. GQH DNAzyme is introduced as a biocatalyst to catalyze the oxidation of L-cysteines to cysteines (thiols to disulfides) to assist SERS signal transduction. This is the first time that the self-assembled split GQH DNAzyme-controlled plasmonic coupling is integrated with SERS sensing. The results reveal the proposed SERS strategy can quantify S. typhimurium with a wide linear range (5 to 10⁵ cfu mL^-1) and a low detection limit (4 cfu mL^-1; n = 5, mean ± standard deviation) and RSD of 7%. The method exhibited preeminent detection performance in spiked samples with recoveries of 93.1-117%. The proposed strategy has great potential for being a versatile SERS platform for detecting a wide spectrum of analytes by replacing them with the corresponding recognition elements. Therefore, this study not only creates a practical platform for pathogenic bacteria identification and related food safety testing and environmental monitoring, but also provides a new paradigm for building SERS sensor. A facile and rapid SERS strategy for S. Typhimurium detection based on hybridization chain reaction (HCR) self-assembled G-quadruplex DNAzyme-controlled plasmonic coupling.

Recent Advances and Applications in Paper-Based Devices for Point-of-Care Testing

Point-of-care testing (POCT), as a portable and user-friendly technology, can obtain accurate test results immediately at the sampling point. Nowadays, microfluidic paper-based analysis devices (μPads) have attracted the eye of the public and accelerated the development of POCT. A variety of detection methods are combined with μPads to realize precise, rapid and sensitive POCT. This article mainly introduced the development of electrochemistry and optical detection methods on μPads for POCT and their applications on disease analysis, environmental monitoring and food control in the past 5 years. Finally, the challenges and future development prospects of μPads for POCT were discussed.

Lab-on-Paper Devices for Diagnosis of Human Diseases Using Urine Samples-A Review

In recent years, microfluidic lab-on-paper devices have emerged as a rapid and low-cost alternative to traditional laboratory tests. Additionally, they were widely considered as a promising solution for point-of-care testing (POCT) at home or regions that lack medical infrastructure and resources. This review describes important advances in microfluidic lab-on-paper diagnostics for human health monitoring and disease diagnosis over the past five years. The review commenced by explaining the choice of paper, fabrication methods, and detection techniques to realize microfluidic lab-on-paper devices. Then, the sample pretreatment procedure used to improve the detection performance of lab-on-paper devices was introduced. Furthermore, an in-depth review of lab-on-paper devices for disease measurement based on an analysis of urine samples was presented. The review concludes with the potential challenges that the future development of commercial microfluidic lab-on-paper platforms for human disease detection would face.

Recent advances in lab-on-paper diagnostic devices using blood samples

Lab-on-paper, or microfluidic paper-based analytical devices (μPADs), use paper as a substrate material, and are patterned with a system of microchannels, reaction zones and sensing elements to perform analysis and detection. The sample transfer in such devices is performed by capillary action. As a result, external driving forces are not required, and hence the size and cost of the device are significantly reduced. Lab-on-paper devices have thus attracted significant attention for point-of-care medical diagnostic purposes in recent years, particularly in less-developed regions of the world lacking medical resources and infrastructures. This review discusses the major advances in lab-on-paper technology for blood analysis and diagnosis in the past five years. The review focuses particularly on the many clinical applications of lab-on-paper devices, including diabetes diagnosis, acute myocardial infarction (AMI) detection, kidney function diagnosis, liver function diagnosis, cholesterol and triglyceride (TG) analysis, sickle-cell disease (SCD) and phenylketonuria (PKU) analysis, virus analysis, C-reactive protein (CRP) analysis, blood ion analysis, cancer factor analysis, and drug analysis. The review commences by introducing the basic transmission principles, fabrication methods, structural characteristics, detection techniques, and sample pretreatment process of modern lab-on-paper devices. A comprehensive review of the most recent applications of lab-on-paper devices to the diagnosis of common human diseases using blood samples is then presented. The review concludes with a brief summary of the main challenges and opportunities facing the lab-on-paper technology field in the coming years.

Stability improvement for dried droplet pretreatment by suppression of coffee ring effect using electrochemical anodized nanoporous tin dioxide substrate

A novel nanoporous analytical platform is reported to improve the stability of the dried droplet method (DDM). This nanoporous platform was made of tin dioxide (Np SnO₂) substrate by electrochemical anodization from tin (Sn) slide. The DDM is a widely used sample pretreatment in analytical chemistry that involves placing a droplet of solution onto the substrate and drying for analytical testing. However, during the droplet drying process, the solutes would converge at the droplet edge and cause inhomogeneous solutes distribution. This is the coffee ring effect (CRE). The Np SnO₂ has irregular nanopores, which allows droplet solutions to penetrate into the substrate rather than spreading out, effectively suppressing CRE. Theoretical models were built to explain the formation of CRE on blank tin (Sn) substrate and suppression of CRE on Np SnO₂. Better results were obtained in detecting lithium (Li) using the Np SnO₂ by laser-induced breakdown spectroscopy (LIBS). The line scanning results indicated that the Li emission line (670.8 nm) intensities on Np SnO₂ substrate had lower relative standard deviation (RSD = 3.3%) than those on Sn substrate (RSD = 31.5%), which illustrate suppression of CRE and stability improvement on Np SnO₂ substrate. Furthermore, Li calibration curves were built for LIBS with DDM. The curve using Np SnO2 substrate had better linearity (R² = 0.997), higher precision (RSD = 4.2%), and higher sensitivity (LOD = 0.13 mg/L) than that by Sn substrate (R² = 0.954, RSD = 17%, and LOD = 1.21 mg/L). All in all, the anodic Np SnO₂ substrate can suppress CRE in DDM and hence improve the stability and precision of subsequent analysis. Graphical abstract.