Colorimetric detection of microRNA miR-21 based on nanoplasmonic core-satellite assembly

Nanoplasmonic biosensors for environmental sustainability and human health

Monitoring the health conditions of the environment and humans is essential for ensuring human well-being, promoting global health, and achieving sustainability. Innovative biosensors are crucial in accurately monitoring health conditions, uncovering the hidden connections between the environment and human well-being, and understanding how environmental factors trigger autoimmune diseases, neurodegenerative diseases, and infectious diseases. This review evaluates the use of nanoplasmonic biosensors that can monitor environmental health and human diseases according to target analytes of different sizes and scales, providing valuable insights for preventive medicine. We begin by explaining the fundamental principles and mechanisms of nanoplasmonic biosensors. We investigate the potential of nanoplasmonic techniques for detecting various biological molecules, extracellular vesicles (EVs), pathogens, and cells. We also explore the possibility of wearable nanoplasmonic biosensors to monitor the physiological network and healthy connectivity of humans, animals, plants, and organisms. This review will guide the design of next-generation nanoplasmonic biosensors to advance sustainable global healthcare for humans, the environment, and the planet.

Enhancing sensitivity towards electrochemical miRNA detection using an affordable paper-based strategy

In the era of liquid biopsy, microRNAs emerge as promising candidates for the early diagnosis and prognosis of cancer, offering valuable insights into the disease's development. Among all the existing analytical approaches, even if traditional approaches such as the nucleic acid amplification ones have the advantages to be highly sensitive, they cannot be used at the point-of-care, while sensors might be poorly sensitive despite their portability. In order to improve the analytical performance of existing electroanalytical systems, we demonstrate how a simple chromatographic paper-based disk might be useful to rationally improve the sensitivity, depending on the number of preconcentration cycles. A paper-based electrochemical platform for miRNA detection has been developed by modifying a paper-based electrode with a methylene blue (MB)-modified single-stranded sequence (ssDNA) complementary to the chosen miRNA, namely miR-224 that is associated with lung cancer. A detection limit of ca. 0.6 nM has been obtained in spiked human serum samples. To further enhance the sensitivity, an external chromatographic wax-patterned paper-based disk has been adopted to preconcentrate the sample, and this has been demonstrated both in standard and in serum solutions. For each solution, three miR-224 levels have been preconcentrated, obtaining a satisfactory lowering detection limit of ca. 50 pM using a simple and sustainable procedure. This approach opens wide possibilities in the field of analytical and bioanalytical chemistry, being useful not only for electrochemistry but also for other architectures of detection and transduction.

Dual amplification-based ultrasensitive and highly selective colorimetric detection of miRNA

In this study, we combined a Pradeep Kumar (PK)-probe with a ligation-transcription-ramified RCA (LTR) dual-amplification system for the isothermal colorimetric detection of miRNA 25-3P, where the PK-probe transformed from its pink color to colorless in the presence of the amplification byproduct pyrophosphate (PPi), thereby allowing the simple naked-eye qualitative detection of the miRNA. Through this double-amplification strategy, the limit of detection reached as low as 91.4 aM-quite extraordinary sensitivity for a colorimetric miRNA detection system based on absorbance readings. Our detection system also operated with high specificity, the result of using two different target-selective ligation steps (linear DNA ligation and circular DNA ligation) mediated by SplintR ligase, and so could discriminate single-mismatched from perfectly matched target sequences. We suspect that this ultrasensitive and selective PK-probe/LTR dual-amplification system should be a great colorimetric diagnostic for the detection of any miRNA with high efficiency.

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.

Dual signal magnification for ultrasensitive biosensing based on well-regulated SERS of AuNTs@AuHg and DSN-assisted amplification

AuNTs@AuHg alloy with well-regulated SERS properties was proposed, which displayed wonderful SERS intensity and effective salt resistance. Using miRNA-21 as a model analyte and combining with DSN-assisted amplification, a dual signal amplification strategy for ultrasensitive miRNA biosensing with a low detection limit (0.53 fM) and satisfactory selectivity was designed.

Highly Sensitive and Specific Mass Spectrometric Platform for miRNA Detection Based on the Multiple-Metal-Nanoparticle Tagging Strategy

The multiple-metal-nanoparticle tagging strategy has generally been applied to the multiplexed detection of multiple analytes of interest such as microRNAs (miRNAs). Herein, it was used for the first time to improve both the specificity and sensitivity of a novel mass spectroscopic platform for miRNA detection. The mass spectroscopic platform was developed through the integration of the ligation reaction, hybridization chain reaction amplification, multiple-metal-nanoparticle tagging, and inductively coupled plasma mass spectrometry. The high specificity resulted from the adoption of the ligation reaction is further enhanced by the multiple-metal-nanoparticle tagging strategy. The combination of hybridization chain reaction amplification and metal nanoparticle tagging endows the proposed platform with the feature of high sensitivity. The proposed mass spectrometric platform achieved quite satisfactory quantitative results for Let-7a in real-world cell line samples with accuracy comparable to that of the real-time quantitative reverse-transcriptase polymerase chain reaction method. Its limit of detection and limit of quantification for Let-7a were experimentally determined to be about 0.5 and 10 fM, respectively. Furthermore, due to the unique way of utilizing the multiple-metal-nanoparticle tagging strategy, the proposed platform can unambiguously discriminate between the target miRNA and nontarget ones with single-nucleotide polymorphisms based on their response patterns defined by the relative mass spectral intensities among the multiple tagged metal elements and can also provide location information of the mismatched bases. Its unique advantages over conventional miRNA detection methods make the proposed platform a promising and alternative tool in the fields of clinical diagnosis and biomedical research.

Poly-adenine regulated DNA density on AuNPs to construct efficient DNA walker for microRNA-21 detection

DNA-modified gold nanoparticles (AuNPs) are useful nanomaterials for detecting multiple molecules. However, their performance is greatly dependent on the density of probe DNA on the surface of AuNPs. Here, we used Poly-adenine (PolyA) to regulate the surface density of probe DNA to achieve a highly efficient DNA walking biosensor system to detection miRNA-21. The movement track of the biosensor system consists of PolyA-DNA probe was connected to AuNPs, and exonuclease III (Exo III) acted as a motor driving the walker movement to achieve signal amplification. By optimizing the length of PolyA, the surface density of probe DNA was changed, thereby affecting the target binding and enzymatic processing of the bound probes, which ultimately enhanced the sensitivity and reduced timeliness of the DNA walker. Furthermore, the designed PolyA-DNA probe exhibits an outstanding sensitivity, due to the effect of density regulation, which is 7.9 times and 11.1 times lower than those of the SH-DNA and the free-DNA, respectively. In addition, the hairpin structure of DNA probe locates fluorophore at a zone adjacent to AuNPs surface, which reduces the background signal by 1.1 times compared with traditional straight probe. In this work, the biosensor system shows a high selectivity towards miRNA-21. Moreover, the biosensor system has been demonstrated to be potentially useful for the miRNA-21 detection in human serum with the recoveries of 93.2%-110.0% and has high repeatability. Considering these advantages, this PolyA-regulated DNA walking biosensor system has great potential as a routine tool for miRNA detection and has wide applications in the field of biomedical analysis.

Hydrogel-Based Colorimetric Assay for Multiplexed MicroRNA Detection in a Microfluidic Device

Although microRNA (miRNA) expression levels provide important information regarding disease states owing to their unique dysregulation patterns in tissues, translation of miRNA diagnostics into point-of-care (POC) settings has been limited by practical challenges. Here, we developed a hydrogel-based microfluidic platform for colorimetric profiling of miRNAs, without the use of complex external equipment for fluidics and imaging. For sensitive and reliable measurement without the risk of sequence bias, we employed a gold deposition-based signal amplification scheme and dark-field imaging, and seamlessly integrated a previously developed miRNA assay scheme into this platform. The assay demonstrated a limit of detection of 260 fM, along with multiplexing of small panels of miRNAs in healthy and cancer samples. We anticipate this versatile platform to facilitate a broad range of POC profiling of miRNAs in cancer-associated dysregulation with high-confidence by exploiting the unique features of hydrogel substrate in an on-chip format and colorimetric analysis.

Detection of Several Homologous MicroRNAs by a Single Smart Probe System Consisting of Linear Nucleic Acid Blockers

We report a universal smart probe (SP) that is capable of detecting several homologous let-7 microRNAs (miRNAs). While the SP is complementary to let-7a, and therefore, strongly binds to this target, due to sequence homology, the SP also has equal propensity to non-specifically hybridize with let-7b and let-7c, which are homologous to let-7a. The fluorescence signal of the SP was switched off in the absence of any homologous member target, but the signal was switched on when any of the three homologous members was present. With the assistance of nucleic acid blockers (NABs), this SP system can discriminate between homologous miRNAs. We show that the SP can discriminate between let-7a and the other two sequences by using linear NABs (LNABs) to block non-specific interactions between the SP and these sequences. We also found that LNABs used do not cross-react with the let-7a target due to the low LNABs:SP molar ratio of 6:1 used. Overall, this SP represents a universal probe for the recognition of a homologous miRNA family. The assay is sensitive, providing a detection limit of 6 fmol. The approach is simple, fast, usable at room temperature, and represents a general platform for the in vitro detection of homologous microRNAs by a single fluorescent hairpin probe.

Biosensors for epigenetic biomarkers detection: A review

Epigenetic inheritance is a heritable change in gene function independent of alterations in nucleotide sequence. It regulates the normal cellular activities of the organisms by affecting gene expression and transcription, and its abnormal expression may lead to the developmental disorder, senile dementia, and carcinogenesis progression. Thus, epigenetic inheritance is recognized as an important biomarker, and the accurate quantification of epigenetic inheritance is crucial to clinical diagnosis, drug development and cancer treatment. Noncoding RNA, DNA methylation and histone modification are the most common epigenetic biomarkers. The conventional biosensors (e.g., northern blotting, radiometric, mass spectrometry and immunosorbent biosensors) for epigenetic biomarkers assay usually suffer from hazardous radiation, complicated manipulation, and time-consuming procedures. To facilitate the practical applications, some new biosensors including colorimetric, luminescent, Raman scattering spectroscopy, electrochemical and fluorescent biosensors have been developed for the detection of epigenetic biomarkers with simplicity, rapidity, high throughput and high sensitivity. In this review, we summarize the recent advances in epigenetic biomarkers assay. We classify the biosensors into the direct amplification-free and the nucleotide amplification-assisted ones, and describe the principles of various biosensors, and further compare their performance for epigenetic biomarkers detection. Moreover, we discuss the emerging trends and challenges in the future development of epigenetic biomarkers biosensors.

Label-free detection of miRNA cancer markers based on terminal deoxynucleotidyl transferase-induced copper nanoclusters

The variations in microRNA (miRNA) expression levels can be useful biomarkers for the diagnosis of different cancers. In this work, a label-free and sensitive fluorescent method for detection of miRNA-21 is described based on duplex-specific nuclease (DSN) assist target recycling and terminal deoxynucleotidyl transferase (TdT) induced copper nanoclusters (CuNCs). In the absence of target, the 3'-phosphorylated probe DNA cannot be hydrolyzed by DSN and extended by TdT, and failed to synthesizing fluorescent CuNCs. However, the target miRNA-21 can caused the digestion of probe DNA with DSN, releasing primer DNA with 3'-OH. After that, the primer DNA can forms long poly T with the assistance of TdT, leading to synthesize high fluorescent CuNCs. The fluorescence change of CuNCs can be used to identify the concentration of target miRNA-21. Under optimal experimental conditions, this strategy could quantitatively detect miRNA-21 down to 18.7 pM. We have also demonstrated the practical application of our proposed method for monitoring miRNA-21 expression levels in cancer cells. Moreover, this method show good specificity for miRNA-21 detection due to the strong preference of DSN for cutting perfectly matched DNA/RNA duplex, which holds great potential for highly specific quantification of biomarkers in bioanalysis and clinical diagnosis.

An ultrasensitive guanine wire-based resonance light scattering method using G-quadruplex self-assembly for determination of microRNA-122

An enzyme-free resonance light scattering (RLS) method is described for the determination of microRNA-122. A guanine nanowire (G-wire) is used that consists of a predesigned DNA1 and a G-quadruplex sequence DNA2. These hybridize with microRNA-122 and partially hybridize with DNA2. After formation of stable double strands with DNA1, DNA2 is released. On addition of K⁺ and Mg²⁺ ions, the G-quadruplex sequences undergo self-assembly to form long filamentous G-wires. This increases the intensity of RLS. A 6.1 pM detection limit was obtained, and the linear response covers the 50 pM to 300 nM microRNA concentration range. The method was successfully applied to the quantitation of microRNA-122 in hepatocellular carcinoma cell lysates. Conceivably, this assay can be extended to other RLS methods for biomarker detection by simply changing the sequence of DNA1. Graphical abstract The G-quadruplex sequences of DNA2 were locked with DNA1. The G-quadruplex fragments of DNA2 were released after the hybridization of microRNA-122 with DNA1. These liberated G-quadruplex sequences were self-assembled into long filamentous guanine nanowires (G-wires) which increased resonance light intensity in the presence of Mg²⁺.

A smartphone-assisted microfluidic chemistry analyzer using image-based colorimetric assays for multi-index monitoring of diabetes and hyperlipidemia

A smartphone-assisted microfluidic chemistry analyzer using an image-based colorimetric detection method was successfully developed for the simultaneous analysis of three diabetes- and hyperlipidemia-related indexes, glucose (GLU), triglyceride (TG), and total cholesterol (TC). A fan-shaped microfluidic chip was designed and optimized to reliably allocate a premixed serum sample into four reaction chambers by a simple pipetting. The color changes of the peroxidase-H₂O₂ enzymatic reactions in the chambers were captured and analyzed using a smartphone-controlled analyzer with a LED light source and a CCD camera. The highly quantitative relationships between the analyte concentrations and the color characteristic values of the green channel of the captured images were successfully established, enabling accurate and reproducible detections of GLU, TG, and TC simultaneously at a low cost. The parallel analyses of 111 serum samples using our system and a conventional chemistry analyzer were conducted, yielding an excellent correlation and consistency between these two systems. This study proved the feasibility of performing the multi-index monitoring of diabetes, hyperlipidemia, and other chronic diseases on a point-of-care platform at a high fidelity, but a low cost.

MicroRNA sensors based on gold nanoparticles

MicroRNAs (miRNAs) are small regulatory RNAs, the dysregulation of which has been associated with the progression of several human diseases, including cancer. Interestingly, these molecules can be used as biomarkers for early disease diagnosis and can be found in a variety of body fluids and tissue samples. However, their specific properties and very low concentrations make their detection rather challenging. In this regard, current detection methods are complex, cost-ineffective, and of limited application in point-of-care settings or resource-limited facilities. Recently, nanotechnology-based approaches have emerged as promising alternatives to conventional miRNA detection methods and paved the way for research towards sensitive, fast, and low-cost detection systems. In particular, due to their exceptional properties, the use of gold nanoparticles (AuNPs) has significantly improved the performance of miRNA biosensors. This review discusses the application of AuNPs in different miRNA sensor modalities, commenting on recently reported examples. A practical overview of each modality is provided, highlighting their future use in clinical diagnosis. Graphical abstract ᅟ.

Electrophoresis separation assisted G-quadruplex DNAzyme-based chemiluminescence signal amplification strategy on a microchip platform for highly sensitive detection of microRNA

We have developed an electrophoresis separation assisted G-quadruplex DNAzyme-based chemiluminescence (CL) signal amplification strategy on a microchip platform for the detection of trace microRNA. This strategy exhibits high sensitivity and specificity for detection of target molecules.

Nanoplasmonic sensors for detecting circulating cancer biomarkers

The detection of cancer biomarkers represents an important aspect of cancer diagnosis and prognosis. Recently, the concept of liquid biopsy has been introduced whereby diagnosis and prognosis are performed by means of analyzing biological fluids obtained from patients to detect and quantify circulating cancer biomarkers. Unlike conventional biopsy whereby primary tumor cells are analyzed, liquid biopsy enables the detection of a wide variety of circulating cancer biomarkers, including microRNA (miRNA), circulating tumor DNA (ctDNA), proteins, exosomes and circulating tumor cells (CTCs). Among the various techniques that have been developed to detect circulating cancer biomarkers, nanoplasmonic sensors represent a promising measurement approach due to high sensitivity and specificity as well as ease of instrumentation and operation. In this review, we discuss the relevance and applicability of three different categories of nanoplasmonic sensing techniques, namely surface plasmon resonance (SPR), localized surface plasmon resonance (LSPR) and surface-enhanced Raman scattering (SERS), for the detection of different classes of circulating cancer biomarkers.

Design and Characterization of a Singly Labeled Fluorescent Smart Probe for In Vitro Detection of miR-21

A sensitive hairpin smart probe (SP) has been developed and tested for its sequence-specificity and sensitivity for detecting microRNAs (miRNAs). The loop sequence of this SP is perfectly complementary to microRNA-21 (miR-21) sequence. This miRNA regulates certain biological processes and has been implicated in certain forms of cancer. The stem of the new SP consists of a fluorophore on one end and multiple guanine bases on the opposing end are used as quenchers. The fluorescence of the SP is significantly quenched by the guanine bases at room temperature and in the absence of the miR-21 target. The presence of miR-21 switches on the fluorescence due to spontaneous hybridization of the SP with this target, which also forces the stem hybrid of the SP apart. This new SP successfully discriminated between the perfect miR-21 target and two closely similar single-base mismatch sequences. When the SP was incubated with the miR-21 at 37 ℃, the hybridization kinetics increased seven times, compared to room temperature hybridization. Overall, this new SP shows good detection sensitivity and gives a limit of detection and limit of quantitation of 14.0 nM and 46.7 nM, respectively. This detection platform represents a simple, fast, mix-and-read homogeneous assay for sequence-specific detection of miR-21, and it can be adapted for other related diagnostic applications.

Highly specific real-time quantification of diverse microRNAs in human samples using universal primer set frame

In this study, one group of universal primer set frame, composed by one reverse transcription (RT) primer frame and a pair of quantitative real-time polymerase chain reaction (qRT-PCR) primer frames, was elaborately screened and designed by homebuilt software for sensitive and specific quantification of diverse miRNAs. The universal primer set frame can be applied for multiplex miRNAs detection by simply changing the RT-X part of RT primer frame and RP-Y part of qRT-PCR reverse primer frame based on target sequence. The maximum similarity of RT-Y, RT-Z and qRT-PCR forward primer to the human genome and human transcriptome is less than 76%, ensuring the high specificity in human sample detection. The high sensitivity and broad dynamic linear range of the developed approaches by using designed primer set frame were demonstrated on the in vitro detection of miR-21 and miR-155, with dynamic range of 10 fM to 10 nM and detection limit of 3.74 × 10^-15 M and 5.81 × 10^-15 M for miR-21 and miR-155, respectively. In particular, the developed assays also have high sequence specificity which could clearly discriminate a single base difference in miRNA sequence. The contents of miR-21 and miR-155 in tissue and serum samples have been successfully detected using the developed assays. Results indicated that miR-21 and miR-155 were elevated in cancer tissue and serum specimens than that of normal samples, implying the developed assays hold a great promise for further application in biomedical research and early clinical diagnosis. More importantly, the primer set frame can be universally used in any miRNA investigation.

Sensitive detection of miRNA by using hybridization chain reaction coupled with positively charged gold nanoparticles

Positively charged gold nanoparticles (+)AuNPs can adsorb onto the negatively charged surface of single-stranded DNA (ssDNA) or double-stranded DNA (dsDNA). Herein, long-range dsDNA polymers could form based on the hybridization chain reaction (HCR) of two hairpin probes (H₁ and H₂) by using miRNA-21 as an initiator. (+)AuNPs could adsorb onto the negatively charged surface of such long-range dsDNA polymers based on the electrostatic adsorption, which directly resulted in the precipitation of (+)AuNPs and the decrease of (+)AuNPs absorption spectra. Under optimal conditions, miRNA-21 detection could be realized in the range of 20 pM-10 nM with a detection limit of 6.8 pM. In addition, (+)AuNPs used here are much more stable than commonly used negatively charged gold nanoparticles ((−)AuNPs) in mixed solution that contained salt, protein or other metal ions. Importantly, the assay could realize the detection of miRNA in human serum samples.

Inhibition of miR-21 by 3'/5'-Serinyl-Capped 2'-O-Methyl RNA Interspersed with 2'-O-(2-Amino-3-Methoxypropyl) Uridine Units

miRNAs are highly conserved class of small ncRNAs whose involvement in human pathophysiologies is extensively investigated. MiR-21 is a well established oncogenic miRNA whose deregulation plays a significant role in onset and progression of cancer. The need of novel approaches to downregulate miR-21 is rapidly expanding. Potent inhibition of miR-21 is achieved by chemically modified 2'-O-methyl RNA oligonucleotide. The serinol capping at 3' and 5'ends and the interspersed 2'-O-(R-2-amino-3-methoxypropyl) uridine units enhance the nuclease resistance and efficacy of 2'-O-methyl RNA for the inhibition of miR-21. This represents a simple and novel modification for developing oligonucleotide-based therapeutics.

Ultrasensitive electrochemical detection of miRNA-21 by using an iridium(III) complex as catalyst

The ultrasensitive electrochemical detection of miRNA-21 was realized by using a novel redox and catalytic "all-in-one" mechanism with an iridium(III) complex as a catalyst. To construct such a sensor, a capture probe (CP) was firstly immobilized onto the gold electrode surface. In the presence of miRNA-21, a sandwiched DNA complex could form between CP and a methylene blue (MB) labeled G-rich detection probe modified onto a gold nanoparticle (AuNP) surface (DP-AuNPs). Upon addition of K(+), the structure of DP changed to a G-quadruplex. Then, the iridium(III) complex could selectively interact with the G-quadruplex, catalyzing the reduction of H2O2, which was accompanied by an electrochemical signal change using MB as an electron mediator. Under optimal conditions, the electrochemical signal of MB reduction peak was proportional to miRNA concentration in the range from 5.0 fM to 1.0 pM, with a detection limit of 1.6 fM. In addition, satisfactory results were obtained for miRNA-21 detection in human serum samples, indicating a potential application of the sensor for bioanalysis.

Visual Detection of Multiplex MicroRNAs Using Cationic Conjugated Polymer Materials

A simple, visual, and specific method for simultaneous detection of multiplex microRNAs (miRNAs) has been developed by integrating duplex-specific nuclease (DSN)-induced amplification with cationic conjugated polymer (CCP) materials. The probe DNA with a complementary sequence to target miRNA is labeled with fluorescein dye (FAM). Without target miRNA, the single-strand DNA probe cannot be digested by DSN. Upon adding CCPs, efficient fluorescence resonance energy transfer (FRET) from CCP to FAM occurs owing to strong electrostatic interactions between CCP and the DNA probe. In the presence of target miRNA, the DNA probe hybridizes with target miRNA followed by digestion to small nucleotide fragments by DSN; meanwhile, the miRNA is released and subsequently interacts again with the probe, resulting in the cycled digestion of the DNA probe. In this case, weak electrostatic interactions between oligonucleotide fragments and CCP lead to inefficient FRET from CCP to FAM. Thus, by triggering the FRET signal from CCP to FAM, miRNA can be specially detected, and the fluorescence color change based on FRET can be visualized directly with the naked eye under an UV lamp. Furthermore, an energy transfer cascade can be designed using CCP and DNA probes labeled at the 5'-terminus with FAM and Cy3 dyes, and the multistep FRET processes offer the ability of simultaneous detection of multiplex miRNAs.

Catalase-functionalized SiO2 nanoparticles mediate growth of gold nanoparticles for plasmonic biosensing of attomolar microRNA with the naked eye

A plasmonic biosensor for specific detection of attomolar microRNA with the naked eye was developed based on catalase/streptavidin-functionalized SiO₂ nanoparticles and hairpin capture probe-coated magnetic beads.

Contact Transfer Printing of Side Edge Prefunctionalized Nanoplasmonic Arrays for Flexible microRNA Biosensor

For a nanoplasmonic approach of wearable biochip platform, understanding correlation between near-field enhancement on nanostructures and sensing capability is a crucial step to improve the sensitivity in biosensing. A novel and effective method is demonstrated to increase sensitivity with the enhanced electric fields and to reduce noise with targeted functionalization enabled by transferring side edge prefunctionalized (SEPF) nanostructure arrays onto flexible substrates. Nanostructure sidewalls have selective biochemically functional terminals for the hybridization of microRNAs (miRNAs) and the immobilization of resonant nanoparticles, thus forming hetero assemblies of the nanostructure and the nanoparticles. The unique configuration has shown ultrasensitive biosensing of miRNA-21 in a 10 × 10^-15 m level by a red-shift in scattering spectra induced by a plasmon coupling. This ultrasensitive SEPF nanostructure arrays are fabricated on a flexible substrate using a contact transfer printing with a release layer of trichloro(1H, 1H, 2H, 2H-perfluorooctyl)silane. The introduction of the release layer at a prefunctionalizing step has proven to provide selective functionalization only on the sidewalls of the nanostructures. This reduces a background noise caused by the scattering from nonspecifically bound nanoparticles on the substrate, thus enabling reliable and precise detection.

Enhanced detection of broadband incoherent light with nanoridge plasmonics

Emerging photonic integrated circuit technologies require integrative functionality at ultrahigh speed and dimensional compatibility with ultrasmall electronics. Plasmonics offers a promise of addressing these challenges with novel nanophotonic approaches for on-chip information processing or sensing applications. Short communication range and strong light-matter interaction enabled by on-chip plasmonics allow us to extend beyond a conventional approach of integrating coherent and narrowband light source. Such hybrid electronic and photonic interconnection desires a on-chip photodetector that is highly responsive to broadband incoherent light, yet provides elegant design for nanoscale integration. Here we demonstrate an ultracompact broadband photodetection with greatly enhanced photoresponsivity using plasmonic nanoridge geometry. The nanoridge photodetector confines a wide spectrum of electromagnetic energy in a nanostructure through the excitation of multiple plasmons, which thus enables the detection of weak and broadband light. With nanoscale design, material, and dimensional compatibility for the integration, the nanoridge photodetector opens up a new possibility of highly sensitive on-chip photodetection for future integrated circuits and sensing applications.

Retracted Article: Graphene oxide/DNA-decorated electrode for the fabrication of microRNA biosensor

A sensitive biosensor for miRNA quantification was fabricated by using a graphene oxide/DNA-decorated electrode.

Bioorthogonal tetrazine-mediated transfer reactions facilitate reaction turnover in nucleic acid-templated detection of microRNA

Tetrazine ligations have proven to be a powerful bioorthogonal technique for the detection of many labeled biomolecules, but the ligating nature of these reactions can limit reaction turnover in templated chemistry. We have developed a transfer reaction between 7-azabenzonorbornadiene derivatives and fluorogenic tetrazines that facilitates turnover amplification of the fluorogenic response in nucleic acid-templated reactions. Fluorogenic tetrazine-mediated transfer (TMT) reaction probes can be used to detect DNA and microRNA (miRNA) templates to 0.5 and 5 pM concentrations, respectively. The endogenous oncogenic miRNA target mir-21 could be detected in crude cell lysates and detected by imaging in live cells. Remarkably, the technique is also able to differentiate between miRNA templates bearing a single mismatch with high signal to background. We imagine that TMT reactions could find wide application for amplified fluorescent detection of clinically relevant nucleic acid templates.

Nanotechnology-based strategies for the detection and quantification of microRNA

MicroRNAs (miRNAs) are important regulators of gene expression, and many pathological conditions, including cancer, are characterized by altered miRNA expression levels. Therefore, accurate and sensitive quantification of miRNAs may result in correct disease diagnosis establishing these small noncoding RNA transcripts as valuable biomarkers. Aiming at overcoming some limitations of conventional quantification strategies, nanotechnology is currently providing numerous significant alternatives to miRNA sensing. In this review an up-to-date account of nanotechnology-based strategies for miRNA detection and quantification is given. The topics covered are: nanoparticle-based approaches in solution, sensing based on nanostructured surfaces, combined nanoparticle/surface sensing approaches, and single-molecule approaches.