Quantum dots-labeled strip biosensor for rapid and sensitive detection of microRNA based on target-recycled nonenzymatic amplification strategy

Field-deployable viral diagnostic tools for dengue virus based on Cas13a and Cas12a

The diagnosis of dengue virus (DENV) has been challenging particularly in areas far from clinical laboratories. Early diagnosis of pathogens is a prerequisite for the timely treatment and pathogen control. An ideal diagnostic for viral infections should possess high sensitivity, specificity, and flexibility. In this study, we implemented dual amplification involving Cas13a and Cas12a, enabling sensitive and visually aided diagnostics for the dengue virus. Cas13a recognized the target RNA by crRNA and formed the assembly of the Cas13a/crRNA/RNA ternary complex, engaged in collateral cleavage of nearby crRNA of Cas12a. The Cas12a/crRNA/dsDNA activator ternary complex could not be assembled due to the absence of crRNA of Cas12a. Moreover, the probe, with 5' and 3' termini labeled with FAM and biotin, could not be separated. The probes labeled with FAM and biotin, combined the Anti-FAM and the Anti-Biotin Ab-coated gold nanoparticle, and conformed sandwich structure on the T-line. The red line on the paper strip caused by clumping of AuNPs on the T-line indicated the detection of dengue virus. This technique, utilizing an activated Cas13a system cleaving the crRNA of Cas12a, triggered a cascade that amplifies the virus signal, achieving a low detection limit of 190 fM with fluorescence. Moreover, even at 1 pM, the red color on the T-line was easily visible by naked eyes. The developed strategy, incorporating cascade enzymatic amplification, exhibited good sensitivity and may serve as a field-deployable diagnostic tool for dengue virus.

Programmable DNA barcode-encoded exponential amplification reaction for the multiplex detection of miRNAs

Multiple analysis of miRNAs is essential for the early diagnosis and monitoring of diseases. Here, a programmable, multiplex, and sensitive approach was developed for one-pot detection of miRNAs by melting temperature encoded sequences and exponential isothermal amplification (E-EXPAR). In the presence of target miRNAs, the corresponding templates initiate the cycles of nicking and polymerization/displacement, generating numerous barcode strands with unique encoding sequences. Subsequently, generated barcode strands hybridize with fluorescent probes and quench the fluorophore by a triplet of G base through a photo-induced electron transfer mechanism. Finally, a melting curve analysis is performed to quantify miRNAs by calculating the rate of fluorescence change at the corresponding melting temperature. Based on this, miRNA-21, miRNA-9, and miRNA-122 were detected with the detection limits of 3.3 fM, 2.9 fM, and 1.7 fM, respectively. This E-EXPAR was also employed to simultaneously detect three miRNAs in biological samples, showing consistent results with RT-qPCR. Overall, this study provides a programmable and universal platform for multiplex analysis of miRNAs, and holds great promise as an alternative to the multiplex analysis in clinical diagnostics and prognostics for nucleic acid detection.

All-in-one detection of breast cancer-derived exosomal miRNA on a pen-based paper chip

Exosomal microRNAs (miRNAs) play a pivotal role in intercellular communication, regulating gene expression in target cells, and hold significant promise as cancer biomarkers for early detection and screening. However, achieving precise and viable detection of exosomal miRNAs remains a challenge. This paper proposes an all-in-one detection strategy for breast cancer-derived exosomal miRNA-21 on a pen-based paper chip (PPC). The PPC is constructed using a modified automatic pen and lateral flow assay (LFA), which results in a cost-effective fabrication process. The user only needs to add the sample and trigger the top of the self-contained PPC after a period of time to complete the entire detection process. To enhance the sensitivity of exosomal miRNA testing, an enzyme-free catalyzed hairpin assembly (CHA) is further introduced, enabling highly sensitive detection of miRNA-21 with a limit of detection (LOD) of 25 fmol. Additionally, the detection of miRNAs in differentially-expressed cells and clinical samples has also been successfully achieved with high specificity. Overall, the proposed PPC provides an effective tool for detecting early cancer, monitoring diseases, and establishing point of care testing (POCT).

Simultaneous detection of AFB1 and aflD gene by "Y" shaped aptamer fluorescent biosensor based on double quantum dots

The developed method for simultaneous detection of aflatoxin B1 (AFB1) and aflD genes can effectively monitor from the source and reduce the safety problems and economic losses caused by the production of aflatoxin, which can be of great significance for food safety regulations. In this paper, we constructed a sensitive and convenient fluorescent biosensor to detect AFB1 and aflD genes simultaneously based on fluorescence resonance energy transfer (FRET) between quantum dots (QDs) and a black hole quenching agent. A stable "Y" shaped aptasensor was employed as the detection platform and a double quantum dot labeled DNA fragment was utilized to be the sensing element in this work. When the targets of AFB1 and aflD genes were presented in the solution, the aptamer in the "Y" shaped probe is specifically recognized by the target. At this time, both Si-carbon quantum dots (Si-CDs) and CdTe QDs are far away from the BHQ1 and BHQ3 to recover the fluorescence. The linear range of the prepared fluorescence simultaneous detection method was as wide as 0.5-500 ng·mL-1 with detection lines of 0.64 ng·mL-1 for AFB1 and 0.5-500 nM with detection lines of 0.75 nM for aflD genes (3σ/k). This fabricated fluorescent biosensor was further validated in real rice flour and corn flour samples, which also achieved good results. The recoveries were calculated by comparing the known and found amounts of AFB1 which ranged from 88.4 to approximately 115.32% in the rice flour samples and 90.7 ~ 102.58% in the corn flour samples. The recoveries of aflD genes ranged from 84.32 to approximately 109.3% in the rice flour samples and 89.48 ~ 100.99% in the corn flour samples. Therefore, the proposed biosensor can significantly improve food safety and quality control through a simple, fast, and sensitive agricultural product monitoring and detection system.

Sensitive and Portable Signal Readout Strategies Boost Point-of-Care CRISPR/Cas12a Biosensors

Point-of-care (POC) detection is getting more and more attention in many fields due to its accuracy and on-site test property. The CRISPR/Cas12a system is endowed with excellent sensitivity, target identification specificity, and signal amplification ability in biosensing because of its unique trans-cleavage ability. As a result, a lot of research has been made to develop CRISPR/Cas12a-based biosensors. In this review, we focused on signal readout strategies and summarized recent sensitivity-improving strategies in fluorescence, colorimetric, and electrochemical signaling. Then we introduced novel portability-improving strategies based on lateral flow assays (LFAs), microfluidic chips, simplified instruments, and one-pot design. In the end, we also provide our outlook for the future development of CRISPR/Cas12a biosensors.

A universal lateral flow assay for microRNA visual detection in urine samples

MicroRNAs (miRNAs) have been emerged as novel and significant biomarkers in liquid biopsy that can be found in different body fluids. Several techniques have been developed and applied for miRNAs analysis, including nucleic acid-based amplification methods, next generation sequencing, DNA microarrays and new genome-editing methods. These methods, however, are time-consuming and require expensive instruments and specially trained personnel. Biosensors, on the other hand, are alternative and valuable analytical/diagnostic tools due to their simplicity, cost-effectiveness, rapid analysis and ease of use. Several biosensors, especially nanotechnology-based ones, have been developed for miRNA analysis that are based either on target amplification or signal amplification and target re-cycling for sensitive detection. At this point of view, we have introduced a new and universal lateral flow assay in combination with reverse transcription - polymerase chain reaction (RT-PCR) and gold nanoparticles as reporters for the detection of miR-21 and miR-let-7a in human urine. It is the first time that such a biosensor has been applied to the detection of microRNAs in urine. As low as 10²-10³ copies of miR-21 and 10^2--10⁴ copies of miR-let-7a added in urine were detectable by the proposed lateral flow assay with great specificity and repeatability (%CVs <4.5%).

CRISPR-based quantum dot nanobead lateral flow assay for facile detection of varicella-zoster virus

Varicella-zoster virus (VZV) infects more than 90% of the population worldwide and has a high incidence of postherpetic neuralgia in elderly patients, seriously affecting their quality of life. Combined with clustered regularly interspaced short palindromic repeats (CRISPR) system, we develop a quantum dot nanobeads (QDNBs) labeled lateral flow assay for VZV detection. Our assay allows the identification of more than 5 copies of VZV genomic DNA in each reaction. The entire process, from sample preparation to obtaining the results, takes less than an hour. In 86 clinical vesicles samples, the test shows 100% concordance with quantitative real-time PCR for VZV detection. Notably, when vesicles are present in specific areas, such as the genitals, our method outperforms clinical diagnosis. Compared to traditional detection methods, only a minute amount of blister fluid is required for accurate detection. Therefore, we anticipate that our method could be translated to clinical applications for specific and rapid VZV detection. KEY POINTS: • CRISPR/Cas12a and quantum dot nanobead-based lateral flow assay achieved 5 copies per reaction for VZV detection • Specific identification of VZV in atypical skin lesions • Results read by the naked eye within one hour.

Electrochemical nanobiosensor based on reduced graphene oxide and gold nanoparticles for ultrasensitive detection of microRNA-128

Acute lymphoblastic leukemia (ALL) is one of the most prevalent cancers in children and microRNA-128 is amongst the most useful biomarkers not only for diagnosis of ALL, but also for discriminating ALL from acute myeloid leukemia (AML). In this study, a novel electrochemical nanobiosensor based on reduced graphene oxide (RGO) and gold nanoparticles (AuNPs) has been fabricated to detect miRNA-128. Cyclic Voltametery (CV), Square Wave Voltametery (SWV) and Electrochemical Impedance Spectroscopy (EIS) have been applied to characterize the nanobiosensor. Hexacyanoferrate as a label-free and methylene blue as a labeling material were used in the design of the nanobiosensors. It was found that the modified electrode has excellent selectivity and sensitivity to miR-128, with a limit of detection of 0.08761 fM in label-free and 0.00956 fM in labeling assay. Additionally, the examination of real serum samples of ALL and AML patients and control cases confirms that the designed nanobiosensor has the potential to detect and discriminate these two cancers and the control samples.

Biosensing chips for cancer diagnosis and treatment: a new wave towards clinical innovation

Recent technological advances in nanoscience and material designing have led to the development of point-of-care devices for biomolecule sensing and cancer diagnosis. In situ and portable sensing devices for bedside, diagnosis can effectively improve the patient’s clinical outcomes and reduce the mortality rate. Detection of exosomal RNAs by immuno-biochip with increased sensitivity and specificity to diagnose cancer has raised the understanding of the tumor microenvironment and many other technology-based biosensing devices hold great promise for clinical innovations to conquer the unbeatable fort of cancer metastasis. Electrochemical biosensors are the most sensitive category of biomolecule detection sensors with significantly low concentrations down to the atomic level. In this sense, this review addresses the recent advances in cancer detection and diagnosis by developing significant biological sensing devices that are believed to have better sensing potential than existing facilities.

Hairpin-inserted cross-shaped DNA nanoprobe for ultrasensitive microRNA detection based on built-in target analogue cycle amplification

It remains technically challenging to develop a sensitive assay system to isothermally amplify the signal for miRNA detection because of its low abundance in tested sample, sequence similarities and existence in complex biological environments. In this study, using miRNA-21 as target model, a hairpin-inserted cross-shaped DNA nanoprobe (CP) with four functional arms is constructed for the ultrasensitive detection of miRNA via one-step built-in target analogue (BTA) cycle-mediated signal amplification. BTA is pre-locked in one arm of CP probe and inactive. In the presence of target miRNA, BTA can be unlocked and initiate an isothermal amplification process. Utilizing as-designed CP probe, miRNA-21 can be detected to down to 500 fM, and the linear response range spans over five orders of magnitude. The nonspecific signal is less than 1% upon nontarget miRNAs. CP probe exhibits ∼six times enhancement in resistance to nuclease degradation and no obvious degradation-induced fluorescence change is detected during the assay period. The recovery yield ranges from 98.2～105.5% in FBS solution. Because of the high sensitivity, desirable specificity, strong anti-interference ability and substantial increase in nuclease resistance, CP probe is a promising tool for the detection of miRNAs in a complex biological milieu.

Advancement in Nanoparticle-Based Biosensors for Point-of-Care In Vitro Diagnostics

Abstract:

Recently, there has been great progress in the field of extremely sensitive and precise detection of bioanalytes. The importance of the utilization of nanoparticles in biosensors has been recognized due to their unique properties. Specifically, nanoparticles of gold, silver, and magnetic plus graphene, quantum dots, and nanotubes of carbon are being keenly considered for utilizations within biosensors to detect nucleic acids, glucose, or pathogens (bacteria as well as a virus). Taking advantage of nanoparticles, faster and sensitive biosensors can be developed. Here we review the nanoparticles' contribution to the biosensors field and their potential applications.

A Polydopamine-Coated Gold Nanoparticles Quenching Quantum Dots-Based Dual-Readout Lateral Flow Immunoassay for Sensitive Detection of Carbendazim in Agriproducts

In this study, a fluorometric and colorimetric dual-readout lateral flow immunoassay (LFIA) using antibody functionalized polydopamine-coated gold nanoparticles (Au@PDAs) as a probe was developed for the detection of carbendazim (CBD). Colloidal gold nanoparticles (AuNPs) were coated with polydopamines (PDA) by the oxidation of dopamine to synthesize Au@PDA nanoparticles. The Au@PDA nanoparticles mediated ZnCdSe/ZnS quantum dots (QDs) fluorescence quenching and recovery, resulting in a reverse fluorescence enhancement detection format of CBD. The CBD detection was obtained by the competition between the CBD and the immobilized antigen for Au@PDAs labelled antibody binding, resulting in a significant fluorescence increase and colorimetry decrease corresponded to the concentration of CBD. Dual readout modes were incorporated into the LFIA using the colorimetry signal under natural light and the fluorescence signal under UV light. The cut-off value in the mode of the colorimetric signal and fluorometric signal for CBD detection was 0.5 μg/mL and 0.0156 μg/mL, respectively. The sensitivity of LFIA of the fluorescence mode was 32 times higher than that of the colorimetry mode. There was negligible cross reactivity obtained by using LFIA for the determination of thiabendazole, benomyl, thiophanate-methyl, and thiophanate-ethyl. Consistent and satisfactory results have been achieved by comparing the results of Au@PDAs-QDs-LFIA and liquid chromatography-tandem mass spectrometry (LC-MS/MS) testing spiked cucumber and strawberry samples, indicating good reliability of the Au@PDAs-QDs-LFIA.

Highly sensitive and portable mRNA detection platform for early cancer detection

Pancreatic cancer, at unresectable advanced stages, presents poor prognoses, which could be prevented by early pancreatic cancer diagnosis methods. Recently, a promising early-stage pancreatic cancer biomarker, extracellular vesicles (EVs) related glypican-1 (GPC1) mRNA, is found to overexpress in pancreatic cancer cells. Current mRNA detection methods usually require expensive machinery, strict preservation environments, and time-consuming processes to guarantee detection sensitivity, specificity, and stability. Herein, we propose a novel two-step amplification method (CHAGE) via the target triggered Catalytic Hairpin Assembly strategy combined with Gold-Enhanced point-of-care-testing (POCT) technology for sensitive visual detection of pancreatic cancer biomarker. First, utilizing the catalyzed hairpin DNA circuit, low expression of the GPC1 mRNA was changed into amplification product 1 (AP1, a DNA duplex) as the next detection targets of the paper strips. Second, the AP1 was loaded onto a lateral flow assay and captured with the gold signal nanoparticles to visualize results. Finally, the detected results can be further enhanced by depositing gold to re-enlarge the sizes of gold nanoparticles in detection zones. As a result, the CHAGE methodology lowers the detection limit of mRNA to 100 fM and provides results within 2 h at 37 °C. Furthermore, we demonstrate the successful application in discriminating pancreatic cancer cells by analyzing EVs' GPC1 mRNA expression levels. Hence, the CHAGE methodology proposed here provides a rapid and convenient POCT platform for sensitive detection of mRNAs through unique probes designs (COVID, HPV, etc.).

Short DNA-catalyzed formation of quantum dot-DNA hydrogel for enzyme-free femtomolar specific DNA assay

Fast, sensitive, specific, and user-friendly DNA assay is a key technique for the next generation point-of-care molecular diagnosis. However, high-cost, time-consuming, and complicated enzyme-based DNA amplification step is essential to achieve high sensitivity. Herein, a short target DNA-catalyzed formation of quantum dot (QD)-DNA hydrogel is proposed as a new DNA assay platform satisfying the above requirements. A single-stranded target DNA catalyzes the opening cycle of DNA hairpin loops, which are quickly self-assembled with DNA-functionalized QDs to generate QD-DNA hydrogel. The three-dimensional hydrogel network allows efficient resonance energy transfer, dramatically lowering the limit of detection down to ~6 fM without enzymatic DNA amplification. The QD-DNA hydrogel also enables a rapid detection (1 h) with high specificity even for a single-base mismatch. The clinical applicability of the QD-DNA hydrogel is demonstrated for the Klebsiella pneumoniae carbapenemase gene, one of the key targets of drug-resistant pathogenic bacteria.

Therapeutic Applications of Functional Nanomaterials for Prostatitis

Prostatitis is a common disease in adult males, with characteristics of a poor treatment response and easy recurrence, which seriously affects the patient's quality of life. The prostate is located deep in the pelvic cavity, and thus a traditional infusion or other treatment methods are unable to easily act directly on the prostate, leading to poor therapeutic effects. Therefore, the development of new diagnostic and treatment strategies has become a research hotspot in the field of prostatitis treatment. In recent years, nanomaterials have been widely used in the diagnosis and treatment of various infectious diseases. Nanotechnology is a promising tool for 1) the accurate diagnosis of diseases; 2) improving the targeting of drug delivery systems; 3) intelligent, controlled drug release; and 4) multimode collaborative treatment, which is expected to be applied in the diagnosis and treatment of prostatitis. Nanotechnology is attracting attention in the diagnosis, prevention and treatment of prostatitis. However, as a new research area, systematic reviews on the application of nanomaterials in the diagnosis and treatment of prostatitis are still lacking. In this mini-review, we will highlight the treatment approaches for and challenges associated with prostatitis and describe the advantages of functional nanoparticles in improving treatment effectiveness and overcoming side effects.

Therapeutic Applications of Functional Nanomaterials for Prostatitis

Prostatitis is a common disease in adult males, with characteristics of a poor treatment response and easy recurrence, which seriously affects the patient’s quality of life. The prostate is located deep in the pelvic cavity, and thus a traditional infusion or other treatment methods are unable to easily act directly on the prostate, leading to poor therapeutic effects. Therefore, the development of new diagnostic and treatment strategies has become a research hotspot in the field of prostatitis treatment. In recent years, nanomaterials have been widely used in the diagnosis and treatment of various infectious diseases. Nanotechnology is a promising tool for 1) the accurate diagnosis of diseases; 2) improving the targeting of drug delivery systems; 3) intelligent, controlled drug release; and 4) multimode collaborative treatment, which is expected to be applied in the diagnosis and treatment of prostatitis. Nanotechnology is attracting attention in the diagnosis, prevention and treatment of prostatitis. However, as a new research area, systematic reviews on the application of nanomaterials in the diagnosis and treatment of prostatitis are still lacking. In this mini-review, we will highlight the treatment approaches for and challenges associated with prostatitis and describe the advantages of functional nanoparticles in improving treatment effectiveness and overcoming side effects.

Rational Design of Dendritic Mesoporous Silica Nanoparticles' Surface Chemistry for Quantum Dot Enrichment and an Ultrasensitive Lateral Flow Immunoassay

Lateral flow immunoassays (LFIAs) have drawn much attention in point-of-care diagnostic applications, and the development of high-performance label materials is the key. In this study, the impact of the surface chemistry of dendritic mesoporous silica nanoparticles (DMSNs) on their enrichment performance toward quantum dots (QDs) and signal amplification of the resultant DMSNs-QDs as label materials have been investigated. A series of DMSNs with controllable amino/thiol group densities have been synthesized. It is demonstrated that the amino groups are beneficial for QD fluorescence preservation, owing to the amino-based surface passivation, while the thiol groups are responsible for increasing the loading capacity of QDs due to the thiol-metal coordination. The optimized DMSNs-QDs labels with an amino density of 153 μmol g^-1 and a thiol density of 218 μmol g^-1 displayed sufficient QD fluorescence preservation (89.4%) and high QD loading capacity (1.55 g g^-1). Ultrasensitive detection of serum amyloid A (SAA) with a detection limit of 10 pg mL^-1 with the naked eye was achieved, which is 1 order of magnitude higher than that reported in the literature. This study provides insights into the development of advanced label materials and an ultrasensitive LFIA for future bioassay applications.

Visual-afterglow dual-mode immunochromatographic strip for 17β-estradiol detection in milk

The continuous intake of 17β-estradiol (E2) residue from animal-derived food may pose a threat to the health of consumers, so the rapid screen and detection of E2 is very necessary. Although visual immunochromatographic strip (ICS) has played a great role in food safety control such as the screen of many food contaminants, it cannot meet the requirements for E2 detection due to the insufficient sensitivity of traditional visual ICS and the low concentration range of estrogen in food. Here, we developed a dual-mode ICS strategy to achieve rapid and highly sensitive detection of E2. Based on the visual detection mode of a competitive ICS, the afterglow detection mode working in fluorescence resonance energy transfer mechanism was introduced by using the afterglow particles (APs) as energy donor and gold nanoparticles (AuNPs) as energy acceptor. In this method, large APs of micron size with superior afterglow were applied as the test zone-fixed fluorescence signal source, thus the contradiction between migration and afterglow characteristics was skillfully resolved. In addition, a 6 W UV lamp was used as the light source to excite APs, and a smartphone was used to capture an image of 0.5 s after the UV light was turned off to effectively remove the autofluorescence from the strips and improve the signal-to-noise ratio. The limit of detection of this afterglow mode was 0.5 ng/mL, twenty times more sensitive than that of visual mode (10 ng/mL). The strategy has been successfully applied to the detection of estradiol in milk and verified by HPLC-FLD.

Nanotechnology in emerging liquid biopsy applications

Liquid biopsy is considered as the most attractive alternative to traditional tissue biopsies. The major advantages of this approach lie in the non-invasive procedure, the rapidness of sample collection and the potential for early cancer diagnosis and real-time monitoring of the disease and the treatment response. Nanotechnology has dynamically emerged in a wide range of applications in the field of liquid biopsy. The benefits of using nanomaterials for biosensing include high sensitivity and detectability, simplicity in many cases, rapid analysis, the low cost of the analysis and the potential for portability and personalized medicine. The present paper reports on the nanomaterial-based methods and biosensors that have been developed for liquid biopsy applications. Most of the nanomaterials used exhibit great analytical performance; moreover, extremely low limits of detection have been achieved for all studied targets. This review will provide scientists with a comprehensive overview of all the nanomaterials and techniques that have been developed for liquid biopsy applications. A comparison of the developed methods in terms of detectability, dynamic range, time-length of the analysis and multiplicity, is also provided.

Utilization of chromogenic enzyme substrates for signal amplification in multiplexed detection of biomolecules using surface mass spectrometry

MicroRNAs (miRNAs) are important post-transcriptional gene regulators and can serve as potential biomarkers for many diseases. Most of the current miRNA detection techniques require purification from biological samples, amplification, labeling, or tagging, which makes quantitative analysis of clinically relevant samples challenging. Here we present a new strategy for the detection of miRNAs with uniformity over a large area based on signal amplification using enzymatic reactions and measurements using time-of-flight secondary ion mass spectrometry (ToF-SIMS), a sensitive surface analysis tool. This technique has high sequence specificity through hybridization with a hairpin DNA probe and allows the identification of single-base mismatches that are difficult to distinguish by conventional mass spectrometry. We successfully detected target miRNAs in biological samples without purification, amplification, or labeling of target molecules. In addition, by adopting a well-known chromogenic enzymatic reaction from the field of biotechnology, we extended the use of enzyme-amplified signal enhancement ToF (EASE-ToF) to protein detection. Our strategy has advantages with respect to scope, quantification, and throughput over the currently available methods, and is amenable to multiplexing based on the outstanding molecular specificity of mass spectrometry (MS). Therefore, our technique not only has the potential for use in clinical diagnosis, but also provides evidence that MS can serve as a useful readout for biosensing to perform multiplexed analysis extending beyond the limitations of existing technology.

Rapid developments in lateral flow immunoassay for nucleic acid detection

Recently, lateral flow assay (LFA) for nucleic acid detection has drawn increasing attention in the point-of-care testing fields. Due to its rapidity, easy implementation, and low equipment requirement, it is well suited for use in rapid diagnosis, food authentication, and environmental monitoring under source-limited conditions. This review will discuss two main research directions of lateral flow nucleic acid tests. The first one is the incorporation of isothermal amplification methods with LFA, which ensures an ultra-high testing sensitivity under non-laboratory conditions. The two most commonly used methodologies will be discussed, namely Loop-mediated Isothermal Amplification (LAMP) and Recombinase Polymerase Amplification (RPA), and some novel methods with special properties will also be introduced. The second research direction is the development of novel labeling materials. It endeavors to increase the sensitivity and quantifiability of LFA testing, where signals can be read and analyzed by portable devices. These methods are compared in terms of limits of detection, detection times, and quantifiabilities. It is anticipated that future research on lateral flow nucleic acid tests will focus on the integration of the whole testing process into a microfluidic system and the combination with molecular diagnostic tools such as clustered regularly interspaced short palindromic repeats to facilitate a rapid and accurate test.

Point-of-care diagnostics approaches for detection of lung cancer-associated circulating miRNAs

Circulating cell-free miRNAs (ccf-miRs) have gained significant interest as biomarkers for lung cancer (LC) diagnosis. However, the clinical application of ccf-miRs is mainly limited by time, cost, and expertise-related problems of existing detection strategies. Recently, the development of different point-of-care (POC) approaches offers useful on-site platforms, because these technologies have important features such as portability, rapid turnaround time, minimal sample requirement, and cost-effectiveness. In this review, we discuss different POC approaches for detecting ccf-miRs and highlight the utility of incorporating nanomaterials for enhanced biorecognition and signal transduction, further improving their diagnostic applicability in LC settings.

Optical Biosensors for the Detection of Rheumatoid Arthritis (RA) Biomarkers: A Comprehensive Review

A comprehensive review of optical biosensors for the detection of biomarkers associated with rheumatoid arthritis (RA) is presented here, including microRNAs (miRNAs), C-reactive protein (CRP), rheumatoid factor (RF), anti-citrullinated protein antibodies (ACPA), interleukin-6 (IL-6) and histidine, which are biomarkers that enable RA detection and/or monitoring. An overview of the different optical biosensors (based on fluorescence, plasmon resonances, interferometry, surface-enhanced Raman spectroscopy (SERS) among other optical techniques) used to detect these biomarkers is given, describing their performance and main characteristics (limit of detection (LOD) and dynamic range), as well as the connection between the respective biomarker and rheumatoid arthritis. It has been observed that the relationship between the corresponding biomarker and rheumatoid arthritis tends to be obviated most of the time when explaining the mechanism of the optical biosensor, which forces the researcher to look for further information about the biomarker. This review work attempts to establish a clear association between optical sensors and rheumatoid arthritis biomarkers as well as to be an easy-to-use tool for the researchers working in this field.

MicroRNA Biomarkers for Infectious Diseases: From Basic Research to Biosensing

In the pursuit of improved diagnostic tests for infectious diseases, several classes of molecules have been scrutinized as prospective biomarkers. Small (18–22 nucleotide), non-coding RNA transcripts called microRNAs (miRNAs) have emerged as promising candidates with extensive diagnostic potential, due to their role in numerous diseases, previously established methods for quantitation and their stability within biofluids. Despite efforts to identify, characterize and apply miRNA signatures as diagnostic markers in a range of non-infectious diseases, their application in infectious disease has advanced relatively slowly. Here, we outline the benefits that miRNA biomarkers offer to the diagnosis, management, and treatment of infectious diseases. Investigation of these novel biomarkers could advance the use of personalized medicine in infectious disease treatment, which raises important considerations for validating their use as diagnostic or prognostic markers. Finally, we discuss new and emerging miRNA detection platforms, with a focus on rapid, point-of-care testing, to evaluate the benefits and obstacles of miRNA biomarkers for infectious disease.

Target-fueled catalytic hairpin assembly for sensitive and multiplex microRNA detection

As a typical strand displacement-based DNA circuit, the catalytic hairpin assembly (CHA) has the potential to transduce and amplify signals for analytical applications, but little practice has been fulfilled in Luminex-based multiple microRNAs (miRNAs) detection. Here, we proposed a target-fueled CHA-based platform for sensitive and multiple miRNAs detection, by virtue of the multiplex characteristic of the Luminex xMAP platform. The cyclic use of target miRNA, which forms a substantial amount of H1-H2 duplexes, has amplified the fluorescent response to achieve sensitive sensing. Key experimental conditions including hairpin probe concentrations, reaction temperature, and concentration of SA-PE were optimized. Liver tumor-related miRNA-21, miRNA-122, and miRNA-222 could be simultaneously detected with LOD of 2 pM. Overall, the proposed method first combined CHA with the Luminex xMAP system to construct a sensitive sensing platform suitable for multiple miRNAs detection in real sample analysis, which could potentially be applied in biomedical research and clinical diagnosis. Graphical abstract.

A handheld continuous-flow real-time fluorescence qPCR system with a PVC microreactor

The polymerase chain reaction (PCR) has unique advantages of sensitivity, specificity and rapidity in pathogen detection, which makes it at the forefront of academia and application in molecular biology diagnosis. In this study, we proposed a hand-held real-time fluorescence qPCR system, which can be used for the quantitative analysis of nucleic acid molecules. For the first time, we use a PVC microreactor which improved the transmittance of the microreactor and made it easy to collect the fluorescence signal. In order to make it portable, the system adopted a passive syringe for sample injection and integrated temperature control and detection with a lithium battery for power supply. What's more, the fluorescence signal was captured by using a smartphone through an external automatic robotic arm. This real-time qPCR system can detect genomic DNA of the H7N9 avian influenza over four orders of magnitude of concentration from 10⁷ to 10⁴ copies per μL. In addition, it was verified that the fluorescence images obtained by this system were clearer than those obtained by a traditional system (using a PTFE spatial PCR microreactor) with two typical dyes and a probe tested-EvaGreen, SYBR Green and FAM.

Exosome-specific tumor diagnosis via biomedical analysis of exosome-containing microRNA biomarkers

Exosome-containing microRNAs (exomiRs) can be employed as potential biomarkers for tumor diagnosis and have drawn much attention in the past few years. However, the separation of exosomes and the detection of exomiRs are still inconvenient or even difficult to implement. Thus, it is important to develop a simple, accurate, and reliable strategy for the separation of exosomes and the biomedical analysis of exomiRs. Herein, a novel exosome-specific tumor diagnosis strategy was constructed by integrating the rapid magnetic exosome-enrichment platform and the Ru(bpy)32+-polymer amplified electrochemiluminescence (ECL) strategy. This strategy realized the rapid and efficient capture of tumor-derived exosomes through a biological-affinity identification platform of the EpCAM antibody. The biomedical analysis of exomiRs achieved a preferable specificity and high sensitivity of 103 particles. Furthermore, we investigated the performance index for clinical blood samples from tumor patients; the results indicated that the exosome-specific tumor diagnosis strategy readily and consistently responded to exomiRs. These results indicated that the exosome-specific tumor diagnosis strategy provided new opportunities for the sensitive and efficient analysis of tumor-derived exomiRs. This strategy greatly simplified the biomedical analysis process and established the non-destructive detection mode of fluid biopsy for tumors.

Nanomaterials for Healthcare Biosensing Applications

In recent years, an increasing number of nanomaterials have been explored for their applications in biomedical diagnostics, making their applications in healthcare biosensing a rapidly evolving field. Nanomaterials introduce versatility to the sensing platforms and may even allow mobility between different detection mechanisms. The prospect of a combination of different nanomaterials allows an exploitation of their synergistic additive and novel properties for sensor development. This paper covers more than 290 research works since 2015, elaborating the diverse roles played by various nanomaterials in the biosensing field. Hence, we provide a comprehensive review of the healthcare sensing applications of nanomaterials, covering carbon allotrope-based, inorganic, and organic nanomaterials. These sensing systems are able to detect a wide variety of clinically relevant molecules, like nucleic acids, viruses, bacteria, cancer antigens, pharmaceuticals and narcotic drugs, toxins, contaminants, as well as entire cells in various sensing media, ranging from buffers to more complex environments such as urine, blood or sputum. Thus, the latest advancements reviewed in this paper hold tremendous potential for the application of nanomaterials in the early screening of diseases and point-of-care testing.

Visual detection for nucleic acid-based techniques as potential on-site detection methods. A review

Nucleic acid-based techniques could achieve highly sensitive detection by amplifying template molecules to millions of folds. It has been one of the most valued analytical methods and is applied in many detection fields, such as diagnosis of infectious diseases, food safety assurance and so on. Nucleic acid-based techniques consist of three steps: nucleic acid extraction, amplification, and product detection. Among them, the detection step plays a vital role because it shows the results directly. As the trend of detection is simple, rapid and instrument-free, it is of necessity to carry out visual detection, where the result read-out could be visible and distinguished by the naked eye. In this critical review, advanced visual detection methods are summarized and discussed in detail, aiming to promote the potential application in on-site detection.

Applications of Catalytic Hairpin Assembly Reaction in Biosensing

Nucleic acids are considered as perfect programmable materials for cascade signal amplification and not merely as genetic information carriers. Among them, catalytic hairpin assembly (CHA), an enzyme-free, high-efficiency, and isothermal amplification method, is a typical example. A typical CHA reaction is initiated by single-stranded analytes, and substrate hairpins are successively opened, resulting in thermodynamically stable duplexes. CHA circuits, which were first proposed in 2008, present dozens of systems today. Through in-depth research on mechanisms, the CHA circuits have been continuously enriched with diverse reaction systems and improved analytical performance. After a short time, the CHA reaction can realize exponential amplification under isothermal conditions. Under certain conditions, the CHA reaction can even achieve 600 000-fold signal amplification. Owing to its promising versatility, CHA is able to be applied for analysis of various markers in vitro and in living cells. Also, CHA is integrated with nanomaterials and other molecular biotechnologies to produce diverse readouts. Herein, the varied CHA mechanisms, hairpin designs, and reaction conditions are introduced in detail. Additionally, biosensors based on CHA are presented. Finally, challenges and the outlook of CHA development are considered.

Au@Pd Nanopopcorn and Aptamer Nanoflower Assisted Lateral Flow Strip for Thermal Detection of Exosomes

Conventional lateral flow biosensing technologies face the dual formidable challenges of poor sensitivity and cumbersome quantitative devices. Here, we developed a Au@Pd nanopopcorn and aptamer nanoflower assisted lateral flow strip (ANAN-LFS) with a thermal signal output to improve detection sensitivity. Moreover, a smartphone-based thermal reader was designed and meticulously optimized to hand-held style, realizing the essential portability of this quantitative device. Experimental studies revealed that the synthesized Au@Pd nanopopcorns clearly red-shifted into the near-infrared region, thus resulting in a higher photothermal response than the standard gold nanoparticles. Aptamer nanoflowers enhanced the system's biorecognition ability significantly compared with single-stranded aptamers due to their functional spatial structure, thus resulting in an even greater improvement in the sensitivity of the ANAN-LFS. With exosomes as model targets, the limit of detection (LOD) was calculated to be 1.4 × 10⁴ exosomes/μL, which exhibited a 71-fold improved analytical performance. The feasibility of this system for detecting spiked biological samples at clinical concentrations was also confirmed. These results suggest that the proposed strategy of integrating a ANAN-LFS with a smartphone-based thermal reader has great potential as a powerful tool for bioanalytical applications, offering the combined unique advantages of high sensitivity and expedient portability.

An electrochemical paper based nano-genosensor modified with reduced graphene oxide-gold nanostructure for determination of glycated hemoglobin in blood

Hemoglobin A1c (HbA1c) is a standard biomarker to measure long-term average glucose concentration for diagnosis and monitoring of diabetes. Various methods have been reported for measuring HbA1c, however, portable and precise determination is still challenging. Herein, a new highly sensitive electrochemical nanobiosensor is developed for the specific determination of HbA1c. A nanocomposite of reduced graphene oxide (rGO) and gold with hierarchical architecture structure was electrochemically deposited on a cheap and flexible graphite sheet (GS) electrode. The nanocomposite increased the surface area, improved the electron transfer on the electrode surface and augmented the signal. It also provided a suitable substrate for linkage of thiolated DNA aptamer as a bioreceptor on the electrode surface by strong covalent bonding. The quantitative label free detection was carried out by differential pulse voltammetry (DPV) in a phosphate-buffered saline (PBS) solution containing redox probe Fe(CN)₆^3-/4-. The detection is based on insulating the surface in presence of HbA1c and decreasing the current, which is directly related to the HbA1c concentration. The nanobiosensor demonstrated high sensitivity of 269.2 μA. cm^-2, wide linear range of 1 nM-13.83 μM with a low detection limit of 1 nM. The biosensor was successfully used for measuring HbA1c in blood real sample. Furthermore, it is promising to use it as a part of a point of care device for low-invasive screening and management of diabetes.

Nanoarchitecture Frameworks for Electrochemical miRNA Detection

With revolutionary advances in next-generation sequencing, the human transcriptome has been comprehensively interrogated. These discoveries have highlighted the emerging functional and regulatory roles of a large fraction of RNAs suggesting the potential they might hold as stable and minimally invasive disease biomarkers. Although a plethora of molecular-biology- and biosensor-based RNA-detection strategies have been developed, clinical application of most of these is yet to be realized. Multifunctional nanomaterials coupled with sensitive and robust electrochemical readouts may prove useful in these applications. Here, we summarize the major contributions of engineered nanomaterials-based electrochemical biosensing strategies for the analysis of miRNAs. With special emphasis on nanostructure-based detection, this review also chronicles the needs and challenges of miRNA detection and provides a future perspective on the presented strategies.