Spatial- and Valence-Matched Neutralizing DNA Nanostructure Blocks Wild-Type SARS-CoV-2 and Omicron Variant Infection.

Natural ligand-receptor interactions that play pivotal roles in biological events are ideal models for design and assembly of artificial recognition molecules. Herein, aiming at the structural characteristics of the spike trimer and infection mechanism of SARS-CoV-2, we have designed a DNA framework-guided spatial-patterned neutralizing aptamer trimer for SARS-CoV-2 neutralization. The ∼5.8 nm tetrahedral DNA framework affords precise spatial organization and matched valence as four neutralizing aptamers (MATCH-4), which matches with nanometer precision the topmost surface of SARS-CoV-2 spike trimer, enhancing the interaction between MATCH-4 and spike trimer. Moreover, the DNA framework provides a dimensionally complementary nanoscale barrier to prevent the spike trimer-ACE2 interaction and the conformational transition, thereby inhibiting SARS-CoV-2-host cell fusion and infection. As a result, the spatial- and valence-matched MATCH-4 ensures improved binding affinity and neutralizing activity against SARS-CoV-2 and its varied mutant strains, particularly the current Omicron variant, that are evasive of the majority of existing neutralizing antibodies. In addition, because neutralizing aptamers specific to other targets can be evolved and assembled, the present design has the potential to inhibit other wide-range and emerging pathogens.

Multichannel Paper Chip-Based Gas Pressure Bioassay for Simultaneous Detection of Multiple MicroRNAs.

Simultaneous detection of multi-biomarkers not only enhances the accuracy of disease diagnosis but also improves detection efficiency and reduces cost. It is vital to achieve portable, simple, low-cost, and simultaneous detection of biomarkers for point-of-care (POC) diagnostics in a low-resource setting. Herein, a multichannel paper chip-based gas pressure bioassay was developed for the simultaneous detection of multiple biomarkers by combining multichannel paper chips with a portable gas pressure meter. Four DNA tetrahedral probes (DTPs) were used as capture probes and were immobilized in different detection zones of the paper chips to improve hybridization efficiency and reduce nonspecific adsorption. The formation of a sandwich structure between target microRNAs (miRNAs), the capture probe, and platinum nanoparticles (PtNPs)-modified complementary DNA (PtNPs-cDNA) transformed biomolecular recognition into quantitative detection of gas pressure. Four lung cancer-related miRNAs were detected simultaneously by a portable gas pressure meter. There is a good linear relationship between gas pressure and the logarithm of miRNA concentration in the range of 10 pM to 100 nM. Compared with single-stranded DNA capture probe, the signal-to-noise (S/N) of DNA tetrahedral probes improved more than 3 times. Using ring-oven washing, the unbound reagents in all channels of the paper chip were simultaneously and continuously washed away, leading to a more cheap, simple, and fast separation than magnetic separation. Therefore, it offers a promising multichannel paper chip-based gas pressure bioassay for portable and simultaneous detection of multiple biomarkers.

A tridecaptin-based fluorescent probe for differential staining of Gram-negative bacteria.

The traditional Gram-staining method, which was invented more than a century ago for differentiating bacteria as Gram positive or Gram negative, is still widely practiced in microbiology. However, Gram staining suffers from several problems which can affect the accuracy of the diagnosis. Here, we report a new Gram-negative-specific fluorescent probe, which is based on a narrow-spectrum antibiotic, tridecaptin A1, and allows selective staining of Gram-negative bacteria in different fixed bacterial samples. Solid-phase peptide synthesis was used to prepare the tridecaptin A1-fluorophore conjugate with a single structure. Labeling selectivity of the probe toward Gram-negative bacteria was confirmed by testing against a panel of bacterial species. By combining the use of a previously reported Gram-positive-specific fluorescent probe, we then further showed the capability of the new probe in differential labeling of a number of complex bacterial samples, which included a mouse gut microbiota cultured in vitro, as well as microbiotas collected from the human oral cavity, soil, and crude oil. High labeling selectivity and coverage were observed in most samples. This method offers a new Gram-negative-specific probe with a defined structure, which allows facile fluorescence-based differentiation of Gram-positive and Gram-negative bacteria for further microbial studies.

Portable detection of serum HER-2 in breast cancer by a pressure-based platform.

A high serum HER-2 extracellular domain (sHER-2 ECD) level has a reverse association with tumor behaviors. In this study, a portable platform for the disease biomarker sHER-2 ECD detection has been established using a pressure-based bioassay. The pressure bioassay consists of a monoclonal antibody immobilized on an eight-well strip, the analyte HER-2, and another monoclonal antibody labeled with the Pt nanoparticles (PtNPs), which have the catalytic ability to decompose H2O2 into H2O and O2(g). The increased pressure due to O2(g) generation is measured by a hand-held pressure meter. A total of 34 serum samples were collected to validate the performance of the pressure bioassay. The results showed that the pressure bioassay platform of HER-2 had a dynamic range from 2 to 50 ng/mL with a limit of detection (LOD) of 2 ng/mL, which was consistent with the ELISA result. In the real serum samples, there was a significant correlation between sHER-2 ECD level and several clinicopathological parameters, especially tissue HER-2 status. Furthermore, the sHER-2 ECD level was found to decrease after targeted therapy in a patient with tHER-2 positive. Overall, this bioassay can facilitate breast cancer diagnosis and prognosis in clinical scenarios and resource-limited areas.

Ultrasensitive and portable assay of mercury (II) ions via gas pressure as readout.

It is of the significant importance to achieve facile and on-site detection of heavy metal ions due to the serious harm to environment and human health. Herein, a facile and portable strategy was developed for detection of Hg2+ via portable pressure meter. Biotinylated DNA1 was conjugated on the surface of streptavidin-coated magnetic beads (MBs) to form MBs-DNA1 complex. In the presence of Hg2+, MBs-DNA1 can hybridize with platinum nanoparticles (PtNPs)-functionalized DNA2 (DNA2-PtNPs) via T-Hg2+-T binding. Then, PtNPs effectively catalyzed the decomposition of H2O2 to generate oxygen, leading to an increase in pressure of sealed well of 96-well plate. The gas pressure was linearly related with the concentration of Hg2+ in the range between 10 pM and 100 nM with a detection limit of 2.79 pM, which is more sensitive than most of the previous reports. The specific T-Hg2+-T binding made it easy to selectively detect Hg2+ even when other metal ions co-existed with Hg2+. Therefore, it offers a cost-effective, rapid, facile and portable way to detect Hg2+ by combining gas-generation reaction with T-Hg2+-T binding, which holds great potential for detecting Hg2+ in water sample.

Ultrasensitive and Facile Detection of MicroRNA via a Portable Pressure Meter.

The upregulation of microRNA (miRNA) is highly related with some kinds of tumor, such as breast, prostate, lung, and pancreatic cancers. Therefore, for an important tumor biomarker, the point-of-care testing (POCT) of miRNA is of significant importance and is in great demand for disease diagnosis and clinical prognoses. Herein, a POCT assay for miRNA detection was developed via a portable pressure meter. Two hairpin DNA probes, H1 and H2, were ingeniously designed and functionalized with magnetic beads (MBs) and platinum nanoparticles (PtNPs), respectively, to form MBs-H1 and PtNPs-H2 complexes. In the presence of target microRNA 21 (miR-21), the cyclic strand displacement reaction (SDR) between MBs-H1 and PtNPs-H2 was triggered to continuously form the MBs-H1/PtNPs-H2 duplex. Owing to the amplification of cyclic SDR, numerous PtNPs were enriched onto the surface of MBs to catalytically decompose H2O2 for the generation of much O2. The gas pressure value has a linear relationship with the logarithmic value of miR-21 concentration in the range of 10 fM to 10 pM. The limit of detection is 7.6 fM, which is more sensitive than that in a number of previous reports. Hairpin DNA probes and magnetic separation highly ensured the specificity and reliability. Single-base mutation was easily discriminated, and the detection of miR-21 in the serum sample achieved satisfactory result. Therefore, it offers a reliable POCT strategy for the detection of miRNA, which is of great theoretical and practical importance for POCT clinical diagnostics.

Point-of-Care Assay of Telomerase Activity at Single-Cell Level via Gas Pressure Readout.

Detection of telomerase activity at the single-cell level is one of the central challenges in cancer diagnostics and therapy. Herein, we describe a facile and reliable point-of-care testing (POCT) strategy for detection of telomerase activity via a portable pressure meter. Telomerase primer (TS) was immobilized onto the surface of magnetic beads (MBs), and then was elongated to a long single-stranded DNA by telomerase. The elongated (TTAGGG)n repeat unit hybridized with several short PtNP-functionalized complementary DNA (PtNPs-cDNA), which specifically enriched PtNPs onto the surfaces of magnetic beads (MBs), which were separated using a magnet. Then, nanoparticle-catalyzed gas-generation reaction converted telomerase activity into significant change in gas pressure. Because of the self-amplification of telomerase and enrichment by magnetic separation, the diluted telomerase equivalent to a single HeLa cell was facilely detected. More importantly, the telomerase in the lysate of 1 HeLa cell can be reliably detected by monitoring change in gas pressure, indicating that it is feasible and possible to study differences between individual cells. The difference in relative activity between different kinds of cancer cells was easily and sensitively studied. Study of inhibition of telomerase activity demonstrated that our method has great potential in screening of telomerase-targeted antitumor drugs as well as in clinical diagnosis.

Hydrogel Droplet Microfluidics for High-Throughput Single Molecule/Cell Analysis.

Heterogeneity among individual molecules and cells has posed significant challenges to traditional bulk assays, due to the assumption of average behavior, which would lose important biological information in heterogeneity and result in a misleading interpretation. Single molecule/cell analysis has become an important and emerging field in biological and biomedical research for insights into heterogeneity between large populations at high resolution. Compared with the ensemble bulk method, single molecule/cell analysis explores the information on time trajectories, conformational states, and interactions of individual molecules/cells, all key factors in the study of chemical and biological reaction pathways. Various powerful techniques have been developed for single molecule/cell analysis, including flow cytometry, atomic force microscopy, optical and magnetic tweezers, single-molecule fluorescence spectroscopy, and so forth. However, some of them have the low-throughput issue that has to analyze single molecules/cells one by one. Flow cytometry is a widely used high-throughput technique for single cell analysis but lacks the ability for intercellular interaction study and local environment control. Droplet microfluidics becomes attractive for single molecule/cell manipulation because single molecules/cells can be individually encased in monodisperse microdroplets, allowing high-throughput analysis and manipulation with precise control of the local environment. Moreover, hydrogels, cross-linked polymer networks that swell in the presence of water, have been introduced into droplet microfluidic systems as hydrogel droplet microfluidics. By replacing an aqueous phase with a monomer or polymer solution, hydrogel droplets can be generated on microfluidic chips for encapsulation of single molecules/cells according to the Poisson distribution. The sol-gel transition property endows the hydrogel droplets with new functionalities and diversified applications in single molecule/cell analysis. The hydrogel can act as a 3D cell culture matrix to mimic the extracellular environment for long-term single cell culture, which allows further heterogeneity study in proliferation, drug screening, and metastasis at the single-cell level. The sol-gel transition allows reactions in solution to be performed rapidly and efficiently with product storage in the gel for flexible downstream manipulation and analysis. More importantly, controllable sol-gel regulation provides a new way to maintain phenotype-genotype linkages in the hydrogel matrix for high throughput molecular evolution. In this Account, we will review the hydrogel droplet generation on microfluidics, single molecule/cell encapsulation in hydrogel droplets, as well as the progress made by our group and others in the application of hydrogel droplet microfluidics for single molecule/cell analysis, including single cell culture, single molecule/cell detection, single cell sequencing, and molecular evolution.

Portable visual quantitative detection of aflatoxin B1 using a target-responsive hydrogel and a distance-readout microfluidic chip.

Aflatoxin B1 (AFB1), as the secondary metabolite of molds, is the most predominant and toxic mycotoxin that seriously threatens the health of humans and animals. In this work, an AFB1-responsive hydrogel was synthesized for highly sensitive and portable detection of AFB1. The AFB1-responsive hydrogel was prepared using an AFB1 aptamer and its two short complementary DNA strands as cross-linkers. For visual detection of AFB1, the hydrogel is preloaded with gold nanoparticles (AuNPs). Upon introduction of AFB1, the AFB1 aptamer binds with AFB1, leading to the disruption of the hydrogel and release of the AuNPs with a distinct color change of the supernatant from colorless to red. In order to lower the detection limit and extend the method to quantitative analysis, a distance-readout volumetric bar chart chip (V-chip) was combined with an AFB1-responsive hydrogel preloaded with platinum nanoparticles (PtNPs). In the presence of AFB1, the hydrogel collapses and releases PtNPs which can catalyze the decomposition of H2O2 to generate O2. The increasing gas pressure moves a red ink bar in the V-chip and provides a quantitative relationship between the distance and the concentration of AFB1. The method was applied for detection of AFB1 in beer, with a detection limit of 1.77 nM (0.55 ppb) where an immunoaffinity column (IAC) of AFB1 was used to cleanup and pre-concentrate the sample, which satisfies the testing requirement of 2.0 ppb set by the European Union. The combination of an AFB1-responsive hydrogel with a distance-based readout V-chip offers a user-friendly POCT device, which has great potential for rapid, portable, selective, and quantitative detection of AFB1 in real samples to ensure food safety and avoid subsequent economic losses.

Evolution of DNA aptamers for malignant brain tumor gliosarcoma cell recognition and clinical tissue imaging.

Gliosarcoma, a variant of glioblastoma multiforme (GBM), is a highly invasive malignant tumor. Unfortunately, this disease still marked by poor prognosis regardless of modern treatments. It is of great significance to discover specific molecular probes targeting gliosarcoma for early cancer diagnosis and therapy. Herein, we have selected a group of DNA aptamers with high affinity and selectivity against gliosarcoma cells K308 using cell-SELEX. All the dissociation constants of these aptamers against gliosarcoma cells were in the nanomolar range and aptamer WQY-9 has the highest affinity and good selectivity among them. Furthermore, truncated aptamer sequence, WQY-9-B, shows similar recognition ability to aptamer WQY-9. In addition, WQY-9-B was found to be able to bind selectively and internalize into cytoplasm of target cancer cell at 37 °C. More importantly, compared to a random sequence, aptamer WQY-9-B showed excellent recognition rate (73.3%) for tissue sections of clinical gliosarcoma samples. These data suggests that aptamer WQY-9-B has excellent potential as an effective molecular probe for gliosarcoma diagnosis.

Biostable L-DNAzyme for Sensing of Metal Ions in Biological Systems.

DNAzymes, an important type of metal ion-dependent functional nucleic acid, are widely applied in bioanalysis and biomedicine. However, the use of DNAzymes in practical applications has been impeded by the intrinsic drawbacks of natural nucleic acids, such as interferences from nuclease digestion and protein binding, as well as undesired intermolecular interactions with other nucleic acids. On the basis of reciprocal chiral substrate specificity, the enantiomer of D-DNAzyme, L-DNAzyme, could initiate catalytic cleavage activity with the same achiral metal ion as a cofactor. Meanwhile, by using the advantage of nonbiological L-DNAzyme, which is not subject to the interferences of biological matrixes, as recognition units, a facile and stable L-DNAzyme sensor was proposed for sensing metal ions in complex biological samples and live cells.

Detection of DNA methyltransferase activity using allosteric molecular beacons.

Abnormal DNA methylation patterns caused by altered DNA methyltransferase (MTase) activity are closely associated with cancer. Herein, using DNA adenine methylation methyltransferase (Dam MTase) as a model analyte, we designed an allosteric molecular beacon (aMB) for sensitive detection of Dam MTase activity. When the specific site in an aMB is methylated by Dam MTase, the probe can be cut by the restriction nuclease DpnI to release a fluorophore labeled aptamer specific for streptavidin (SA) which will bind to SA beads to generate highly fluorescent beads for easy signal readout by a microscope or flow cytometer. However, aMBs maintain a hairpin structure without the binding ability to SA beads in the absence of Dam MTase, leading to weakly fluorescent SA beads. Unlike the existing signal amplified assays, our method is simpler and more convenient. The high performance of the aptamer and the easy bead separation process make this probe superior to other methods for the detection of MTase in complex biological systems. Overall, the proposed method with a detection limit of 0.57 U mL(-1) for Dam MTase shows great potential for further applications in the detection of other MTases, screening of MTase inhibitors, and early diagnosis of cancer.

Using aptamers to elucidate esophageal cancer clinical samples.

The epithelial cell adhesion molecule (EpCAM) is closely correlated with the occurrence and development of various cancers of epithelial origin. This study tested, for the first time, the ability of EpCAM aptamer SYL3C to detect EpCAM expression in 170 cases of esophageal cancer (EC) and precancerous lesions, as well as 20 cases of EC series samples, using immunofluorescence imaging analysis. Corresponding antibodies were used as control. EpCAM overexpression was 98% in both esophageal squamous cell carcinoma (ESCC) and esophageal adenocarcinoma (EACA) and 100% in metastasis, but no EpCAM overexpression was detected in undifferentiated EC (UEC). Significant differences were noted among various stages of differentiation (p < 0.05) with the degree of differentiation inversely correlated with the expression of EpCAM. Overexpressed EpCAM was detected in severe dysplasia, but negative in mild to moderate dysplasia and benign esophageal lesions. In a competitive binding experiment, EpCAM aptamer generated a staining pattern similar to that of antibody, but the binding sites with EpCAM were different. Based on these results, it can be concluded that EpCAM is suitable for use as an EC biomarker, therapeutic target, and effective parameter for tumor transfer and prognosis evaluation by aptamer SYL3C staining.

Selection and Application of DNA Aptamer Against Oncogene Amplified in Breast Cancer 1.

Amplified in breast cancer 1 (AIB1), also known as steroid receptor coactivator 3 (SRC-3), is a transcriptional coactivator that interacts with nuclear receptors and other transcription factors to enhance their effects on target gene transcription. AIB1, which acts as a major oncogene, is highly expressed in many human cancers, and has been demonstrated to be a key regulator for tumor initiation, progression, metastasis, invasion, and survival. Recruitment of the transcriptional factor CBP/p300 by CBP/p300-interaction domain (CID) of AIB1 is essential for its transcriptional activation function. In this research, we isolated a DNA aptamer AY-3 that binds to AIB1-CID from a random oligonucleotide library using in vitro screening technology-Systematic Evolution of Ligands by EXponential enrichment (SELEX). The binding affinity of the aptamer to AIB1-CID fusion protein is in the nanomolar range. More importantly, the aptamer was found to disrupt in the interaction between p300 and AIB1. This aptamer has great potential to serve as a therapeutic agent for cancer by inhibiting the coactivation of AIB1.

Simple and Rapid Functionalization of Gold Nanorods with Oligonucleotides Using an mPEG-SH/Tween 20-Assisted Approach.

DNA conjugated gold nanorods (AuNRs) are widely applied for nanostructure assembly, gene therapy, biosensing, and drug delivery. However, it is still a great challenge to attach thiolated DNA on AuNRs, because the positively charged AuNRs readily aggregate in the presence of negatively charged DNA. This article reports an mPEG-SH/Tween 20-assisted method to load thiolated DNA on AuNRs in 1 h. Tween 20 and mPEG-SH are used to synergistically displace CTAB on the surface of AuNRs by repeated centrifugation and resuspension, and thiolated DNA are attached to AuNRs in the presence of 1 M NaCl, 100 mM MgCl2, or 100 mM citrate. AuNRs with different sizes and aspect ratios can be functionalized with DNA by this method. The number of DNA loaded on each AuNR can be easily controlled by the concentrations of mPEG-SH and Tween 20 or the ratio between DNA and AuNR. Functionalized AuNRs were used for nanoparticle assembly and cancer cell imaging to confirm that DNA anchored on the surface of AuNRs retains its hybridization and molecular recognition capability. The new method is easy, rapid, and robust for the preparation of DNA functionalized AuNRs for a variety of applications such as cancer therapy, drug delivery, self-assembly, and imaging.

A controllable aptamer-based self-assembled DNA dendrimer for high affinity targeting, bioimaging and drug delivery.

Targeted drug delivery is important in cancer therapy to decrease the systemic toxicity resulting from nonspecific drug distribution and to enhance drug delivery efficiency. We have developed an aptamer-based DNA dendritic nanostructure as a multifunctional vehicle for targeted cancer cell imaging and drug delivery. The multifunctional DNA dendrimer is constructed from functional Y-shaped building blocks with predesigned base-pairing hybridization including fluorophores, targeting DNA aptamers and intercalated anticancer drugs. With controllable step-by-step self-assembly, the programmable DNA dendrimer has several appealing features, including facile modular design, excellent biostability and biocompatibility, high selectivity, strong binding affinity, good cell internalization efficiency, and high drug loading capacity. Due to the unique structural features of DNA dendrimers, multiple copies of aptamers can be incorporated into each dendrimer, generating a multivalent aptamer-tethered nanostructure with enhanced binding affinity. A model chemotherapeutic anticancer drug, doxorubicin, was delivered via these aptamer-based DNA dendrimers and exerted a potent toxicity for target cancer cells (human T cell acute lymphoblastic leukemia cell line) with low side effects for the non-target cells (human Burkitt's lymphoma cell line). This controllable aptamer-based DNA dendrimer is a promising candidate for biomedical applications.

Evolution of DNA aptamers through in vitro metastatic-cell-based systematic evolution of ligands by exponential enrichment for metastatic cancer recognition and imaging.

Metastasis, the capability of tumor cells to spread and grow at distant sites, is the primary factor in cancer mortality. Because metastasis in sentinel lymph nodes suggests the original spread of tumors from a primary site, the detection of lymph node involvement with cancer serves as an important prognostic and treatment parameter. Here we have developed a panel of DNA aptamers specifically binding to colon cancer cell SW620 derived from metastatic site lymph node, with high affinity after 14 rounds of selection by the cell-SELEX (systematic evolution of ligands by exponential enrichment) method. The binding affinities of selected aptamers were evaluated by flow cytometry. Aptamer XL-33 with the best binding affinity (0.7 nM) and its truncated sequence XL-33-1 with 45 nt showed excellent selectivity for recognizing target cell SW620. The binding entity of the selected aptamer has been preliminarily determined as a membrane protein on the cell surface. Tissue imaging results showed that XL-33-1 was highly specific to the metastatic tumor tissue or lymph node tissue with corresponding cancer metastasis and displayed an 81.7% detection rate against colon cancer tissue with metastasis in regional lymph nodes. These results suggest that XL-33-1 has great potential to become a molecular imaging agent for early detection of lymph node tissue with colon cancer metastasis. More importantly, this study clearly demonstrates that DNA ligands selectively recognizing metastatic cancer cells can be readily generated by metastatic-cell-based SELEX for potential applications in metastatic cancer diagnosis and treatment.

MicroRNA-33b Inhibits Breast Cancer Metastasis by Targeting HMGA2, SALL4 and Twist1.

MicroRNAs are a class of small noncoding RNAs that regulate gene expression post-transcriptionally either by inhibiting protein translation or by causing the degradation of target mRNAs. Current evidence indicates that miR-33b is involved in the regulation of lipid metabolism, cholesterol homeostasis, glucose metabolism and several human diseases; however, whether miR-33b contributes to the pathogenesis of human cancers and participates in the regulation of self-renewal of human cancer stem cells remains unknown. Here, we report the identification of miR-33b as a negative regulator of cell stemness and metastasis in breast cancer. Compared with paired normal breast tissues, miR-33b expression is downregulated in breast tumor samples and is inversely correlated with lymph node metastatic status. Ectopic overexpression of miR-33b in highly metastatic breast cancer cells suppresses cell self-renewal, migration and invasion in vitro and inhibits lung metastasis in vivo. Conversely, miR-33b knockdown promotes the self-renewal, migration and invasion capabilities of noncancerous mammary epithelial cells. The mechanism through which miR-33b inhibits the stemness, migration and invasion of breast cancer cells is by targeting HMGA2, SALL4 and Twist1. These data indicate that miR-33b acts as an onco-suppressive microRNA in breast cancer progression by inhibiting the stemness and metastasis of breast cancer cells.

Target-responsive DNA hydrogel mediated "stop-flow" microfluidic paper-based analytic device for rapid, portable and visual detection of multiple targets.

A versatile point-of-care assay platform was developed for simultaneous detection of multiple targets based on a microfluidic paper-based analytic device (µPAD) using a target-responsive hydrogel to mediate fluidic flow and signal readout. An aptamer-cross-linked hydrogel was used as a target-responsive flow regulator in the µPAD. In the absence of a target, the hydrogel is formed in the flow channel, stopping the flow in the µPAD and preventing the colored indicator from traveling to the final observation spot, thus yielding a "signal off" readout. In contrast, in the presence of a target, no hydrogel is formed because of the preferential interaction of target and aptamer. This allows free fluidic flow in the µPAD, carrying the indicator to the observation spot and producing a "signal on" readout. The device is inexpensive to fabricate, easy to use, and disposable after detection. Testing results can be obtained within 6 min by the naked eye via a simple loading operation without the need for any auxiliary equipment. Multiple targets, including cocaine, adenosine, and Pb(2+), can be detected simultaneously, even in complex biological matrices such as urine. The reported method offers simple, low cost, rapid, user-friendly, point-of-care testing, which will be useful in many applications.

Highly sensitive and selective detection of miRNA: DNase I-assisted target recycling using DNA probes protected by polydopamine nanospheres.

Based on the protective properties of polydopamine nanospheres for DNA probes against nuclease digestion, we have developed a DNase I-assisted target recycling signal amplification method for highly sensitive and selective detection of miRNA.