MicroRNA Detection with Turnover Amplification via Hybridization-Mediated Staudinger Reduction for Pancreatic Cancer Diagnosis

Near-infrared light-induced homogeneous photoelectrochemical biosensor based on 3D walking nanomotor-assisted CRISPR/Cas12a for ultrasensitive microRNA-155 detection

The dysregulation of microRNA (miRNA) expression levels is intricately linked to a myriad of human diseases, and the precise and delicate detection thereof holds paramount significance in the realm of clinical diagnosis and therapy. Herein, a near-infrared (NIR) light-mediated homogeneous photoelectrochemical (PEC) biosensor was constructed for miRNA-155 detection based on NaYF4: Yb, Tm@ZnIn2S4 (NYF@ ZIS) coupled with a three-dimensional (3D) walking nanomotor-assisted CRISPR/Cas12a strategy. The upconverted light emitted by the NYF in the visible and UV region upon NIR light excitation could be utilized to excite ZIS to produce a photocurrent response. The presence of target miRNA-155 initiated an amplification reaction within the 3D walking nanomotor, resulting in the production of multiple nucleic acid fragments. These fragments could activate the collateral cleavage capability of CRISPR/Cas12a, leading to the indiscriminate cleavage of single-stranded DNA (ssDNA) on ALP-ssDNA-modified magnetic beads and the subsequent liberation of alkaline phosphatase (ALP). The released ALP facilitated the catalysis of ascorbic acid 2-phosphate to generate ascorbic acid as the electron donor to capture the photogenerated holes on the NYF@ZIS surface, resulting in a positively correlated alteration in the photocurrent response. Under optimal conditions, the NIR light-initiated homogeneous PEC biosensor had the merits of good linear range (0.1 fM to 100 pM), an acceptable limit of detection (65.77 aM) for miRNA-155 detection. Considering the pronounced sensitivity, light stability, and low photodamage, this strategy presents a promising platform for detecting various other miRNA biomarkers in molecular diagnostic practice.

PdPt@SnS2 Nanosheets for a Novel Ultrasensitive Electrochemiluminescence Biosensor for miRNA-21 Assay

PdPt nanosheets decorated on SnS2 nanosheets (i.e., PdPt@SnS2 NSs) were fabricated for a novel electrochemiluminescence (ECL) biosensor for ultrasensitive detection of miRNA-21 based on catalytic hairpin assembly (CHA) cycles. The PdPt@SnS2 NSs serve as both the main luminophore and a highly effective coreaction accelerator in the ECL biosensor. In the CHA cycles, more miRNA-21 is captured, and the performance of the ECL biosensor is improved. When miRNA-21 is present, the hairpin chain DNA1 (i.e., H1) is opened, and the ferrocene (Fc)-modified hairpin chain DNA2 (i.e., Fc-H2) hybridizes with as-opened H1 by replacing miRNA-21 to stimulate CHA cycles of miRNA-21. During the CHA cycles, Fc-H2 quenches the ECL signal to monitor miRNA-21. As a result, the ECL biosensor shows ultrasensitive and highly selective detection of miRNA-21 from 1 aM to 1 nM with a detection limit (LOD) of 0.02 aM. In addition, the ECL biosensor exhibits excellent practicality for miRNA-21 detection in human serum samples.

Functionalized nanomaterials-based electrochemiluminescent biosensors and their application in cancer biomarkers detection

To detect a range of trace biomarkers associated with human diseases, researchers have been focusing on developing biosensors that possess high sensitivity and specificity. Electrochemiluminescence (ECL) biosensors have emerged as a prominent research tool in recent years, owing to their potential superiority in low background signal, high sensitivity, straightforward instrumentation, and ease of operation. Functional nanomaterials (FNMs) exhibit distinct advantages in optimizing electrical conductivity, increasing reaction rate, and expanding specific surface area due to their small size effect, quantum size effect, and surface and interface effects, which can significantly improve the stability, reproducibility, and sensitivity of the biosensors. Thereby, various nanomaterials (NMs) with excellent properties have been developed to construct efficient ECL biosensors. This review provides a detailed summary and discussion of FNMs-based ECL biosensors and their applications in cancer biomarkers detection.

Quantitative Analysis of Mitochondrial RNA in Living Cells with a Dual-Color Imaging System

Accurate quantification and dynamic expression profiling of mitochondrial RNA (mtRNA for short) are critical for illustrating their cellular functions. However, there lack methods for precise detection of mtRNA in situ due to the delivery restrictions and complicated cellular interferences. Herein, a dual-color imaging system featured with signal amplification and normalization capability for quantitative analysis of specific mtRNA is established. As a proof-of-concept example, an enzyme-free hairpin DNA cascade amplifier fine-tailored to specifically recognize mtRNA encoding NADH dehydrogenase subunit 6 (ND6) is employed as the signal output module and integrated into the biodegradable mitochondria-targeting black phosphorus nanosheet (BP-PEI-TPP) to monitor spatial-temporal dynamics of ND6 mtRNA. An internal reference module targeting β-actin mRNA is sent to the cytoplasm via BP-PEI for signal normalization, facilitating mtRNA quantification inside living cells with a degree of specificity and sensitivity as high as reverse transcription-quantitative polymerase chain reaction (RT-qPCR). With negligible cytotoxicity, this noninvasive "RT-qPCR mimic" can accurately indicate target mtRNA levels across different cells, providing a new strategy for precise analysis of subcellular RNAs in living systems.

Primer exchange reaction-amplified protein-nucleic acid interactions for ultrasensitive and specific microRNA detection

Protein-nucleic acid interactions are not only fundamental to genetic regulation and cellular metabolism, but molecular basis to artificial biosensors. However, such interactions are generally weak and dynamic, making their specific and sensitive quantitative detection challenging. By using primer exchange reaction (PER)-amplified protein-nucleic acid interactions, we here design a universal and ultrasensitive electrochemical sensor to quantify microRNAs (miRNAs) in blood. This PER-miR sensor leverages specific recognition between S9.6 antibodies and miRNA/DNA hybrids to couple with PER-derived multi-enzyme catalysis for ultrasensitive miRNA detection. Surface binding kinetic analysis shows a rational K_d (8.9 nM) between the miRNA/DNA heteroduplex and electrode-attached S9.6 antibody. Based on such a favorable affinity, the programmable PER amplification enables the sensor to detect target miRNAs with sensitivity up to 90.5 aM, three orders of magnitude higher than that without PER in routine design, and with specificity of single-base resolution. Furthermore, the PER-miR sensor allows detecting multiple miRNAs in parallel, measuring target miRNA in lysates across four types of cell lines, and differentiating tumor patients from healthy individuals by directly analyzing the human blood samples (n = 40). These advantages make the sensor a promising tool to enable quantitative sensing of biomolecular interactions and precision diagnostics.

Partial collapse of DNA tetrahedron for miRNA assay with duplex-specific nuclease-assisted amplification

We establish a facile electrochemical approach for detecting miRNA. Programmable DNA tetrahedron is designed using thiol groups for electrode modification, the amino group for the localization of electrochemical species and a hairpin structure that responds to target miRNA. In addition, duplex-specific nuclease-assisted amplification helps improve the sensitivity of this biosensor. The target-initiated partial collapse of the DNA tetrahedron event integrates recognition, electrode immobilization, signal recruitment and amplification. By measuring the sharp silver stripping peak, the highly sensitive detection of miRNA is achieved, which also performs satisfactorily challenging biological samples. This method is featured with simple operation, high sensitivity and practical utility, exhibiting great application potential in clinical diagnosis.

Superior graphdiyne self-powered biosensing platform with highly sensitivity and reliability for dual-mode detection of MicroRNA by integrating T7 Exonuclease and 3D DNA walker induced rolling circle amplification

A highly sensitivity self-powered biosensor is developed based on T7 exonuclease (T7 Exo) and 3D DNA walker induced rolling circle amplification (RCA) for electrochemical/colorimetric dual-mode detection of microRNA-21 (miRNA-21) with improved reliability. Taking its advantage of fascinating properties, such as high structure defects and good conductivity, graphdiyne is prepared and used to prepare high-performance enzyme biofuel cell. T7 Exo-assisted 3D DNA walker target recognition triggers RCA reaction to obtain a significantly amplified signal response. A capacitor is integrated to the enzyme biofuel cell to further amplify the electrochemical output signal of the self-powered biosensor. In detection system, glucose oxidase catalyzes glucose oxidation to produce hydrogen peroxide, and 3,3',5,5'-tetramethylbenzidine (TMB) is then catalyzed to generate colored products, so as to achieve the colorimetric detection of the target. Analysis signals of diverse modes are recorded independently. Consequently, detection of microRNA with improved reliability and wider signal response range are achieved by electrochemical/colorimetric dual-mode with detection limits of 0.15 and 33 fM (S/N = 3) respectively. In addition, the proposed self-powered biosensor successfully applied for the detection of miRNA-21 in human serum samples, confirming its practical applicability in clinical diagnosis. It is powerfully anticipated the proposed self-powered biosensor possesses great potential to be applied to other biomedical domains.

Dual-AND Logic Gate-Based Strip Assay for Amplified Detection of Four miRNAs and Diagnosis of Lung Cancer

The detection of circulating tumor microRNAs (miRNAs) holds great promise for the noninvasive and early-stage diagnosis of cancer. However, the low abundance of lung cancer-related miRNAs and the false-positive results of single miRNA detection limited the development of strip-based point-of-care testing methods in clinic. We developed a duplex-specific nuclease (DSN)-mediated and dual-AND logic gate-based triple-line lateral flow strip detection system for the rapid and simultaneous detection of four miRNAs of lung cancer in a single strip test. This system combines DSN-mediated signal amplification with AND logic gate-based simple signal output. Meanwhile, the limit of detection of this platform was calculated to be 26.51 fM. Furthermore, this assay was used to detect lung cancer-related miRNAs from serum in a homogeneous and separation-free format, which could discriminate lung cancer patients from healthy individuals with an accuracy of 100%. Our approach provides a simple and easy-to-handle method for the diagnosis of lung cancer in clinic.

Niosome-Assisted Delivery of DNA Fluorescent Probe with Optimized Strand Displacement for Intracellular MicroRNA21 Imaging

MicroRNAs play a vital role in cancer development and are considered as potential biomarkers for early prognostic assessment. Here, we propose a novel biosensing system to achieve fluorescence imaging of miRNA21 (miR21) in cancer cells. This system consists of two components: an optimized "off-on" double-stranded DNA (dsDNA) fluorescent for miR21 sensing by efficient strand-displacement reaction and a potent carrier vesicle, termed niosome (SPN), to facilitate the efficient intracellular delivery of the dsDNA probe. A series of dsDNA probes based on fluorescence energy resonance transfer (FRET) was assembled to target miR21. By optimizing the appropriate length of the reporter strand in the dsDNA probe, high accuracy and sensitivity for miR21 recognition are ensured. To overcome the cellular barrier, we synthesized SPN with the main components of a nonionic surfactant Span 80 and a cationic lipid DOTAP, which could efficiently load dsDNA probes via electrostatic interactions and potently deliver the dsDNA probes into cells with good biosafety. The SPN/dsDNA achieved efficient miR21 fluorescent imaging in living cells, and could discriminate cancer cells (MCF-7) from normal cells (L-02). Therefore, the proposed SPN/dsDNA system provides a powerful tool for intracellular miRNA biosensing, which holds great promise for early cancer diagnosis.

Highly Efficient Electrochemiluminescence of MnS:CdS@ZnS Core-Shell Quantum Dots for Ultrasensitive Detection of MicroRNA

In this work, a novel electrochemiluminescence (ECL) biosensor was developed for ultrasensitive detection of microRNA let-7a (miRNA let-7a) based on MnS:CdS@ZnS core-shell quantum dots (QDs) as ECL luminophores with high ECL efficiency. Impressively, compared to the CdS:Mn@ZnS QDs prepared by ionic doping with ECL efficiency of 0.87%, MnS:CdS@ZnS QDs synthesized by bimetallic clusters (Cd₂Mn₂O₄) doping exhibited high ECL efficiency of up to 15.84% with S₂O₈^2- as cathodic coreactant due to the elimination of the dopants size mismatch and "self-purification" effect, which could achieve the surface defect passivation of MnS:CdS@ZnS QDs for effectively improving the ECL emission. Furthermore, with the help of strand displacement amplification (SDA), the trace target miRNA let-7a was able to be converted to a number of output DNA labeled with ferrocene (Fc) to construct an ultrasensitive ECL biosensor. The well-designed ECL biosensor for miRNA let-7a exhibited high stability and excellent sensitivity of a concentration variation from 10 aM to 1 nM and a low detection limit of 4.1 aM, which was further applied to the analysis of miRNA let-7a from cancer cell (MCF-7) lysate. Thus, this strategy provides a novel method to prepare high-efficient ECL emitters for the construction of ECL biosensing platforms in biological fields and clinical diagnosis.

Fluorescence DNA Switch for Highly Sensitive Detection of miRNA Amplified by Duplex-Specific Nuclease

DNA is a type of promising material for the construction of sensors owing to its sequence programmability to control the formation of certain structures. MicroRNA (miRNA) can be applied as promising biomarkers for the diagnosis of a range of diseases. Herein, a novel fluorescent sensing strategy for miRNA is proposed combining duplex-specific nuclease (DSN)-mediated amplification and dumbbell DNA structural switch. Gold nanoparticles (AuNPs) are employed, which provide a 3D reaction interface. They also act as effective fluorescence quenchers. The proposed sensor exhibits high sensitivity (sub-femtomolar level) with a wide dynamic range. In addition, excellent selectivity to distinguish homology sequences is achieved. It also performs satisfactorily in biological samples. Overall, this fluorescent sensor provides a powerful tool for the analysis of miRNA levels and can be applied for related biological studies and clinical diagnosis.

Endogenous MicroRNA Accurate Diagnostics to Guide Photothermal Therapy

Developing an intelligent theranostic nanoplatform with satisfied diagnostic accuracy and therapeutic efficiency holds great promise for personalized nanomedicine. Herein, we constructed a smart nanodevice for the accurate diagnosis of endogenous cancer microRNA (miRNA) biomarkers and efficient photothermal therapy (PTT). The nanodevice was composed of polydopamine (PDA)-functionalized CuS nanosheets (CuS@PDA NSs) and three elaborate DNA hairpin probes (TDHPs). The CuS@PDA NSs acted as efficient delivery vehicles and photothermal agents. They provided a large surface area available for an efficient and facile loading of TDHPs and a high-fluorescence (FL) quenching performance to achieve an ultralow background signal. The intracellular miRNA triggered TDHPs to assemble into three-arm branched junction structures for a strong fluorescence recovery as output signals to discriminate cancer cells from normal cells with an excellent sensitivity. The CuS@PAD NSs showed a good photothermal conversion efficiency in the near-infrared II (NIR II) region to mediate a good photothermal performance to kill cancer cells. A remarkable antitumor therapeutic effect was achieved in vivo. This work integrated highly sensitive detection to endogenous cancer biomarkers and valid therapeutic potency to tumor-bearing mice, indicating its promising biomedical applications.

Shedding Light on DNA-Based Nanoprobes for Live-Cell MicroRNA Imaging

DNA-based nanoprobes integrated with various imaging signals have been employed for fabricating versatile biosensor platforms for the study of intracellular biological process and biomarker detection. The nanoprobes developments also provide opportunities for endogenous microRNA (miRNA) in situ analysis. In this review, the authors are primarily interested in various DNA-based nanoprobes for miRNA biosensors and declare strategies to reveal how to customize the desired nanoplatforms. Initially, various delivery vehicles for nanoprobe architectures transmembrane transport are delineated, and their biosecurity and ability for resisting the complex cellular environment are evaluated. Then, the novel strategies for designing DNA sequences as target miRNA specific recognition and signal amplification modules for miRNA detection are presented. Afterward, recent advances in imaging technologies to accurately respond and produce significant signal output are summarized. Finally, the challenges and future directions in the field are discussed.

A glucose/O2 biofuel cell integrated with an exonuclease-powered DNA walker for self-powered sensing of microRNA

With the aid of an exonuclease-powered DNA walker, the amount of glucose oxidase immobilized on the bioanode can be facilely tailored by varying the concentration of microRNA-141, so a glucose/O₂ biofuel cell is employed as a self-powered sensor for sensitive and selective detection of microRNA-141.

DNA-Templated Bioorthogonal Reactions via Catalytic Hairpin Assembly for Precise RNA Imaging in Live Cells

There has been a significant interest in developing proximity-induced bioorthogonal reactions for nucleic acid detection and imaging, owing to their high specificity and tunable reaction kinetics. Herein, we reported the first design of a fluorogenic sensor by coupling a bioorthogonal reaction with a DNA cascade circuit for precise RNA imaging in live cells. Two DNA hairpin probes bearing tetrazines or vinyl ether caged fluorophores were designed and synthesized. Upon target mRNA triggering catalytic hairpin assembly, the chemical reaction partners were brought in a spatial proximity to yield high effective concentrations, which dramatically facilitated the bioorthogonal reaction efficiency to unmask the vinyl ether group to activate fluorescence. The proposed fluorogenic sensor was demonstrated to have a high signal-to-noise ratio up to ∼30 fold and enabled the sensitive detection of target mRNA with a detection limit of 4.6 pM. Importantly, the fluorogenic sensor presented low background signals in biological environments due to the unique "click to release" feature, avoiding false positive results caused by unspecific degradation. We also showed that the fluorogenic sensor could accurately image mRNA in live cells and distinguish the relative mRNA expression levels in both tumor and normal cells. Benefiting from these significant advantages, our method provides a useful tool for basic studies of bioorthogonal chemistry and early clinical diagnosis.

Sensitive Quantification of MicroRNA in Blood through Multi-amplification Toehold-Mediated DNA-Strand-Displacement Paper-Spray Mass Spectrometry (TSD-PS MS)

Accurate quantification of disease-signature microRNAs (miRNAs) in biomedical samples is in high demand for clinical diagnosis but still challenging because of low miRNAs abundance and complicating interferences in the milieus. Here, we report a multi-amplification strategy for blood miRNAs analysis based on paper-spray mass spectrometry (PS MS). A toehold-mediated DNA-strand-displacement reaction (TSD) is employed to amplify the signal chain and to ensure the specificity. The signal chain is then cleaved by UV to release signal molecules for detection. Moreover, paper spray can efficiently filter out the interfering substances in blood and further enhances the detecting sensitivity. This concept is successfully demonstrated in the prototype detection of a cancer biomarker miRNA-141 in blood and serum. The proposed TSD-PS MS approach provides an efficient way for sensitive detection of oligonucleotides with low concentration in complicating milieus.

Multicolor fluorescence encoding of different microRNAs in lung cancer tissues at the single-molecule level

The simultaneous detection of multiple microRNAs (miRNAs) will facilitate early clinical diagnosis. Herein, we demonstrate the integration of multicolor fluorophore-encoded cascade signal amplification with single-molecule detection for simultaneous measurement of different miRNAs in lung cancer tissues. This assay involves two linear templates and two circular templates without the requirement of any fluorescent-labeled probes. The binding of target miRNAs to their corresponding linear templates initiates the cyclic strand displacement amplification, generating many triggers which can specifically hybridize with the corresponding biotin-labeled AP probes to initiate the apurinic/apyrimidic endonuclease 1-assisted cyclic cleavage reaction for the production of more biotin-labeled primers for each miRNA. The resultant two primers can react with their corresponding circular templates to initiate rolling circle amplification which enables the incorporation of Cy5-dCTP/Cy3-dGTP nucleotides, resulting in the simultaneous production of abundant biotin-/multiple Cy5/Cy3-labeled DNA products. After magnetic separation and exonuclease cleavage, the amplified products release abundant Cy5 and Cy3 fluorescent molecules which can be simply monitored by single-molecule detection, with Cy3 indicating miR-21 and Cy5 indicating miR-155. This assay involves three consecutive amplification reactions, enabling the conversion of extremely low abundant target miRNAs into large numbers of Cy5/Cy3 fluorophore-encoded DNA products which can release abundant fluorescent molecules for the generation of amplified signals. This assay exhibits high sensitivity, good selectivity, and the capability of multiplexed assay. This method can simultaneously quantify miR-155 and miR-21 in living cells and in lung cancer tissues, and it can distinguish the expression of miRNAs between non-small cell lung cancer patients and healthy persons. The accuracy and reliability of the proposed method are further validated by quantitative reverse transcription polymerase chain reaction.

From Passive Signal Output to Intelligent Response: "On-Demand" Precise Imaging Controlled by Near-Infrared Light

"On-demand" accurate imaging of multiple intracellular miRNAs will significantly improve the detection reliability and accuracy. However, the "always-active" design of traditional multicomponent detection probes enables them to passively recognize and output signals as soon as they encounter targets, which will inevitably impair the detection accuracy and, inevitably, result in false-positive signals. To address this scientific problem, in this work, we developed a near-infrared (NIR) light-activated multicomponent detection intelligent nanoprobe for spatially and temporally controlled on-demand accurate imaging of multiple intracellular miRNAs. The proposed intelligent nanoprobe is composed of a rationally designed UV light-responsive triangular DNA nano sucker (TDS) and upconversion nanoparticles (UCNPs), named UCNPs@TDS (UTDS), which can enter cells autonomously through endocytosis and enable remote regulation of on-demand accurate imaging for multiple intracellular miRNAs using NIR light illumination at a chosen time and place. It is worth noting that the most important highlight of the UTDS we designed in this work is that it can resist nonspecific activation as well as effectively avoid false-positive signals and improve the accuracy of imaging of multiple intracellular miRNAs. Moreover, distinguishing different kinds of cell lines with different miRNA expressions levels can be also achieved through this NIR light-activated intelligent UTDS, showing feasible prospects in precise imaging and disease diagnosis.

Sensitive detection of miRNA based on enzyme-propelled multiple photoinduced electron transfer strategy

A method is presented that uses photoinduced electron transfer (PET) for the determination of microRNAs (miRNAs) in clinical serum samples and complicated cell samples by using a smartphone. miRNA-21 is adopted as a model analyte. A 3'-phosphorylated DNA probe containing AgNCs is synthesized and hybridized with miRNA-21. Subsequently, the probe is cleaved specifically by duplex-specific nuclease to form 3'-hydroxylated products, then extended by terminal deoxynucleotidyl transferase (TdT) with superlong G for G-quadruplex/hemin units fabrication. In this way, PET occurred between AgNCs and produced G-quadruplex/hemin units, leading to the fluorescence quenching of AgNCs. Notably, the fluorescence images can be captured and translated into digital information by smartphone, resulting in a direct quantitative determination of miRNA. As a result, our strategy for miRNA assay is achieved with a satisfactory detection limit of 1.43 pM. Interestingly, TdT-propelled G-quadruplex/hemin units as multiple electron acceptors promote the sensitivity of miRNA monitoring. Different miRNAs assays are realized by adjusting the complimentary sequences of DNA probe. These qualities not only broaden the practical application of PET-based strategy, but also provide a new insight into the nucleic acid detection. Schematic representation of AgNCs and enzyme-propelled photoinduced electron transfer strategy. It has been successfully applied for detection of miRNA by image analysis software. The method displays portability and accuracy for miRNA determination, meeting the potential for biochemical and clinical applications in resource-limited settings.

A hybridization-based dual-colorimetric kit for circulating cancer miRNA detection

A dual-colorimetric miRNA detection kit that can simultaneously detect two miRNAs with high sensitivity and selectivity is developed, and the data can be read by the naked eye easily. The kit is able to distinguish the patients from healthy people and achieve lung cancer diagnosis using clinical serum samples in a short time.

Co-catalytic Fc/HGQs/Fe3O4 nanocomposite mediated enzyme-free electrochemical biosensor for ultrasensitive detection of MicroRNA

Herein, a novel co-catalytic ferrocene/hemin/G-quadruplexes/Fe₃O₄ nanoparticles (Fc/HGQs/Fe₃O₄) nanocomposite was synthesized to significantly magnify the electrochemical signal of ferrocene (Fc) using the synergistic catalysis of hemin/G-quadruplexes (HGQs) and Fe₃O₄ nanoparticles as hydrogen peroxide enzyme mimics for the construction of ultrasensitive electrochemical biosensors. The fabricated electrochemical biosensor can achieve ultrasensitive detection of miRNA-155 ranging from 0.1 fM to 1 nM, as well as a limit of detection of 74.8 aM. This strategy provides a new route to exploring efficient signal labels for signal amplification and provides an impetus to find novel methods for the construction of biosensors for biological detection and the early clinic diagnosis of diseases.

Sensitive detection of RNA based on concatenated self-fuelled strand displacement amplification and hairpin-AgNCs

Herein, a self-fuelled amplification strategy (SFAS) is proposed, in which two strand displacement amplification (SDA) processes were concatenated for the proliferation of ssDNA. The ssDNA then initiated a polymerase action and caused the destruction of hairpin-templated silver nanoclusters (AgNCs), resulting in decreased fluorescence for sensing miRNA-21. This SFAS-based sensor is less complicated in design and facile in operation, because of the easy concatenation of SDA and mutual enzymes used in the signal output process. The sensitivity of this SFAS-based miRNA sensor was 1.78 × 10^-11 M with a linear relationship in the range 0.02-1.0 × 10^-9 M, and the recoveries of this method ranged from 82.07% to 106.58% with an average RSD of 10.96%.

Design, synthesis and application in biological imaging of a novel red fluorescent dye based on a rhodanine derivative

A novel acceptor–donor–acceptor type molecule, namely 2-triphenylamine-1,3-dia[2-(3-ethyl-4-oxo-thiazolidin-2-ylidene)-malononitrile] (2RDNTPA), is designed and synthesized. 2RDNTPA exhibits a large Stokes shift of 244 nm and red fluorescence emission of 629 nm with a decent photoluminescence quantum yield of 13%. Furthermore, as a potential red fluorescent dye, 2RDNTPA can be applied in fluorescence imaging of living cancer cells (HepG2) with negligible cytotoxicity and a half maximal inhibitory concentration much more than 100 μM.

2RDNTPA can be applied in fluorescence imaging of living cancer cells (HepG2) with red emission of 620 nm and negligible cytotoxicity with a half maximal inhibitory concentration much more than 100 μM.

Plasmonic Modulation of the Upconversion Luminescence Based on Gold Nanorods for Designing a New Strategy of Sensing MicroRNAs

Upconversion nanoparticles (UCNPs) have potential applications in biosensing and bioimaging. However, the UCNPs-based sensors constructed by luminescence resonance energy transfer (LRET) always suffer from low quenching efficiency, hindering their application. Therefore, exploring a new strategy to resolve this issue is highly desirable. Herein, a strategy based on the surface plasmon resonance (SPR) effect of gold nanorods (AuNRs) is presented. The luminescence of UCNPs was modulated by adjusting the SiO₂ thickness of AuNRs@SiO₂ and the structure of UCNPs; an enhancement factor of ≈50 times was obtained. Based on the results of the SPR effect of AuNRs, we designed two kinds of potential upconversion microRNA sensors using microRNA-21 as a model to resolve the problem of the lower quenching efficiency resulting from a dye as a quencher. Studies revealed that the proposed strategy could be successfully used to construct upconversion microRNA sensors for avoiding the limitation of the low quenching efficiency. The sensitivity was ≈10 000 times higher than that of the upconversion sensor using dyes as quenchers. Importantly, the assay of microRNA-21 was successfully achieved using this sensor in human serum samples and human breast cancer cell (MCF-7) lysates. It provides a new method for designing upconversion microRNA sensors and may have potential for use in biosensing and bioimaging.