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Monitoring the fluctuation of adenosine triphosphate (ATP) level in living cells could promote the understanding of metabolic pathways and cell biology. Here, we proposed a highly sensitive, selective, and biocompatible nanoprobe with core-shell structure, namely Au NBPs@ZIF-8 composed by gold nanobipyramids (Au NBPs) and zeolitic imidazolate framework-8 (ZIF-8), for monitoring intracellular ATP level fluctuation in living cells. Because the coordination between ATP and Zn

Bacterial infections seriously threaten human health and also bring huge financial burden. It is critical to construct multifunctional platforms for effectively inactivating bacteria right after point-of-care testing (POCT). Chemiluminescence (CL) bioassays are considered as powerful candidates for POCT as they are free from using an excitation light source, while the flash-type emission limits their further application. Herein, a CL system with long, persistent, and intensive intensity was constructed based on the peroxidase-like property of 4-mercaptophenylboronic acid (MPBA)-functionalized CuSe nanoprobes (CuSe

Monitoring tumor biomarkers is crucial for cancer diagnosis, progression monitoring, and treatment. However, identifying single or multiple biomarkers with the same spatial locations can cause false-positive feedback. Herein, we integrated the DNA tetrahedron (DT) structures with logic-responsive and signal amplifying capability to construct transmembrane DNA logic nanodevices (TDLNs) for the

Developing a coreactant-free ratiometric electrochemiluminescence (ECL) strategy based on a single luminophore to achieve more accurate and sensitive microRNA (miRNA) detection is highly desired. Herein, utilizing zinc-metal organic frameworks (Zn-MOFs) as the single luminophore, a novel dual-potential ratiometric ECL biosensor was constructed for ultrasensitive detection of miRNA-133a. The as-prepared Zn-MOFs exhibited simultaneous cathode and anode ECL emission. Furthermore, the Zn-MOFs were confirmed to be a multichannel ECL sensing platform with excellent annihilation and coreactant ECL emission. The corresponding ECL behaviors were investigated in detail. Benefiting from the hybridization chain reaction (HCR) amplification technology, N,N-diethylethylenediamine (DEAEA) was modified on hairpin DNA, and the gained products loaded with quantities of DEAEA enhanced the anodic ECL intensity of Zn-MOFs. In the presence of miRNA-133a, the ECL intensity ratio of anode to cathode (Ia/Ic) was significantly increased, which realized the ultrasensitive ratiometric detection of miRNA-133a. In addition, without an exogenous coreactant, the biosensor revealed superb accuracy and stability. Under optimal conditions, the detection linearity of miRNA-133a was from 50 aM to 50 fM with a low detection limit of 35.8 aM (S/N = 3). This is the first work to use Zn-MOFs as a single emitter for reliable ratiometric ECL bioanalysis, which provides a new perspective for fabricating a ratiometric ECL biosensor platform.

Plasmon resonance energy transfer (PRET) in hybrid plasmonic-molecular systems has a broad range of applications from catalysis to analytical/biochemical/biophysical imaging and sensing. Herein, we experimentally and theoretically probed the influence of the distance (d) between the plasmonic nanoparticle and the conjugated molecules on the PRET efficiency (ηPRET) using two PRET systems, which involved tetramethylrhodamine (TAMRA) or Cy3 molecules as acceptors and single spherical gold nanoparticles (AuNPs) as donors. The double-stranded DNA (dsDNA) sequences precisely adjusted within 12.0 nm were utilized as a donor-acceptor spacer. Then, the ηPRET of the two systems under varied d-values was available from the reduction of the scattering intensity of AuNPs. Both experimental and quasi-static approximation data show that ηPRET displays a d-value-dependent decay function. This study would provide new insights into optimal PRET-based chemical/biochemical sensors.

Isothermal nucleic acid amplification technology has been widely adopted for analytical chemistry with the purpose of sensitivity improvement. Herein we present an ultrasensitive concatenated hybridization chain reaction (C-HCR) based surface-enhanced Raman scattering (SERS) immunoassay by forming antibody-antigen-aptamer heterosandwich structures with the model analyte of total prostate specific antigens (tPSA). In the C-HCR, two HCRs, one proceeds with two hairpins and the other with four biotin-modified hairpins, are coupled, making the formation of DNA nanofirecrackers with the lengths longer than 200 nm and more than four hundred million binding sites of streptavidin modified enzymes. These types of DNA nanofirecrackers through the aptamer encoded linker strand to form heterosandwich structures could provide a general signal application platform such as enzyme catalysis with high amplification efficiency. As a proof of concept, the Au@Ag core-shell nanostructure based SERS immunoassay with excellent signal amplification has been developed by employing the streptavidin modified alkaline phosphatase (SA-ALP) through its catalysis of 2-phospho-l-ascorbic acid trisodium salt (AAP) to form Au@Ag core-shell nanostructures via the formation of ascorbic acid (AA) to reduce AgNO

Peroxynitrite (ONOO-), a highly reactive nitrogen species (RNS) generated mainly in mitochondria, has been identified to be associated with numerous pathophysiological processes, and thus accurate ONOO- imaging with superior sensitivity and selectivity is highly desirable. Herein, we prepared a new type of carbon quantum dots (CQDs) with mitochondria-targeting function without the aid of any targeting molecules via a simple one-step hydrothermal route. The as-prepared CQDs not only displayed relatively uniform size distribution, few surface defects, high photostability, and excellent biocompatibility but also exhibited good selective fluorescence turn-off response toward ONOO-, owing to the oxidation of amino groups on the surface of carbon dots. A great linear correlation between the quenching efficiency and ONOO- concentration in the range from 0.15 to 1.0 μM with a detection limit of 38.9 nM is shown. Moreover, the as-prepared CQDs acting as a functional optical probe through a self-targeting mechanism were successfully applied for in situ visualization of endogenous ONOO- generated in the mitochondria of live cells, providing great promise for elucidating the complex biological roles of ONOO- in related pathological processes.

DNA logic nanodevices have prospects in molecular recognitions but still face challenges in achieving DNA computation-controlled regulation in specific compartments of living cells. By incorporating the i-motif sequence and ATP aptamers into a Y-shaped DNA (Y-DNA) structure, and applying gold nanoparticles (AuNPs) as the transporting carrier, herein we present a new type of DNA logic nanodevices to monitor the ATP levels in lysosomes of living cells. Triple energy transfers including dual fluorescent resonance energy transfers (FRETs) and a nanometal surface energy transfer (NSET) occurred in the DNA logic nanodevices. It was identified that the proposed nanodevices perform an AND logic operation to output FRET signals only when an endogenous proton and ATP simultaneously exist in the cellular microenvironment. Owing to the use of the i-motif sequence, the nanodevices have lysosome-recognizing capacity without causing alkalization of the acidic organelle, making DNA computation-controlled regulation at the level of cellular organelles achievable. These DNA logic nanodevices show high application prospects in lysosome-related cellular function and disease treatment.

MicroRNAs (miRNAs) are found in extremely low concentrations in cells, so highly sensitive quantitation is a great challenge. Herein, a simple dual-amplification strategy involving target-activated catalytic hairpin assembly (CHA) coupled with multiple fluorophores concentrated on one X-shaped DNA is reported. In this strategy, four hairpin probes (H1, H2, H3, and H4) are modified with FAM and BHQ1 at both sticky ends, while a circulating hairpin probe (H0) is used to activate CHA circuits once it binds to complementary sequences in the target miR-21 (T). The powerful dual-amplification cascades in Forster resonance energy transfer (FRET)-based nonenzymatic nucleic acid circuits are triggered by T-H0-activated formation of the X-shaped DNA nanostructure, freeing T-H0 for the next CHA reaction cycle. CHA circuits increase the fluorescence due to the wide distance between FAM and BHQ1 in the formed X-shaped DNA nanostructure, resulting in signal amplification and highly sensitive detection of miR-21, with a limit of detection (LOD, 3σ) of 0.025 nM, which is 25.6 or 57.6 times lower than that obtained through a single-amplification strategy without multiple fluorophores on one X-shaped DNA or CHA circuit. Furthermore, this cascade reaction was completed in 45 min, effectively avoiding target degradation. This new enzyme-free signal amplification strategy holds promising potential for sensitively detecting different DNA or RNA sequences by simply adapting the fragment of the H0 sequence complementary to the target.

Forster resonance energy transfer (FRET) from fluorescent nanoparticles to fluorescent dyes is an attractive approach for bioanalysis in living cells. However, the luminescence of the nanoparticle donor/acceptor has not been effectively used to produce highly efficient FRET because the distance between the energy donor and energy acceptor is often larger than the effective FRET radius (about 10 nm) and the uncontrolled rotational and translational diffusion of luminophores. Here, we develop an aggregation-enhanced energy transfer strategy that can overcome the impedance for effective energy transfer. The functional nanoprobes, named TPP-CDs-FITC, are carbon dots (CDs) functionalized with triphenylphosphine (TPP) and ∼117 fluorescein 5-isothiocyanate (FITC) on the surface. In dispersed solution, the 3.8 nm TPP-CDs-FITC show weak FRET efficiency (15.4%). After TPP-instructed mitochondrial targeting, enhanced FRET efficiency (53.2%) is induced due to the aggregation of TPP-CDs-FITC selectively triggered by adenosine triphosphate (ATP) in the mitochondria. The enhanced FRET efficiency can be attributed to the joint effect of the augment of numbers of FITC acceptors within 10 nm from dispersed 117 to aggregated 5499 and the restricted rotational and translational motions of TPP-CDs donors and FITC acceptors. Ultimately, we successfully observe the fluctuations of ATP levels in the mitochondria using the aggregation-enhanced energy transfer strategy of the TPP-CDs-FITC nanodevice.

High sensitivity and accuracy are two key issues that are critical for electrochemiluminescence (ECL) detection, especially for low-abundance nucleic acid detection. However, research on the construction of biosensors has mainly been through a step-by-step approach, which will increase the systematic error and affect the accuracy of the detection. Here we propose a novel strategy of introduction of a branched hybridization chain reaction (bHCR) circuit to a terbium(II) organic gel (TOG) modified electrode in one step to achieve both sensitive detection and simplified modification steps. The sensitivity of the biosensor was elevated by the cascade bHCR circuit that was activated by miRNA-141 and operated like a molecular machine to form hyperbranched DNA nanostructures. Benefiting from molecular programming, the obtained nanostructures carried a large number of dopamine molecules, which can effectively quench the ECL signal of emitters and achieve a low limit of detection (0.18 fM). Impressively, the proposed one-step approach was almost the easiest way to modify nucleic acids to electrodes. In this way, the introduction of a high-molecular-weight DNA structure in one step avoided the errors that may result from the stepwise modification of low-molecular-weight nucleic sequences into the electrode. Considering the accessible operation, favorable performance, and high universality of this strategy, this work may be used to analyze other microRNAs and further clinical diagnosis.

Photothermal effects (PTEs) have been greatly concerned with the fast development of new photothermal nanomaterials. Herein we propose a photothermal immunoassay (PTIA) by taking mycotoxins (AFB1) as an example based on the PTEs of plasmonic Cu2–xSe nanocrystals (NCs). By loading plasmonic Cu2–xSe NCs into liposomes to form photothermal soft nanoballs (ptSNBs), on which aptamer of AFB1 previously assembled, a sandwich structure of AFB1 could be formed with the aptamer on ptSNBs and capture antibody. The heat released from the ptSNBs under NIR irradiation, owing to the plasmonic photothermal light-to-heat conversion through photon–electron–phonon coupling, makes the temperature of substrate solution increased, and the increased temperature has a linear relationship with the AFB1 content. Owing to the large amounts of plasmonic Cu2–xSe NCs in the ptSNBs, the PTEs get amplified, making AFB1 higher than 1 ng/mL detectable in food even if with a rough homemade immunothermometer. The proposal of PTIA opens a ne...

In this work, we propose a three-layer hierarchical hybridization chain reaction (3L hHCR) composed of 1stHCR, 2ndHCR, and 3rdHCR to achieve robust signal amplification efficiency and broaden the applied range of HCR-based systems. In principle, the execution of superior HCR generates the formation of the initiator (named as 2ndI or 3rdI) of the subordinate HCR that relies on the introduction of the target sequence (1stI). To avoid the high background signal of the 3L hHCR system, a strategy of "splitting reconstruction" was adopted. The initiator of the subordinate HCR was designed as two separate fragments (splitting) that are obtained together (reconstruction) for the motivation of the subordinate HCR after the completion of the superior HCR. The implementation of the entire 3L hHCR system generates significant fluorescence recovery that derives from the impediment of Forster resonance energy transfer between fluorophore and quencher; thus, ultrasensitive detection of 1stI in the range of 50 pM to 10 nM can be achieved. Surprisingly, when the concentration of 1stI is lower than 1 nM, the 3L hHCR shows excellent ability to discriminate against various concentrations of 1stI, which is better than that of the 2L hHCR I system. Due to the hierarchical self-assembly mechanism, the 3L hHCR can also be reliably operated as a cascade AND logic gate with a high specificity and molecular keypad lock with a prompt error-reporting function. Furthermore, the 3L hHCR-based molecular keypad lock also shows potential application in the accurate diagnosis of cancer. The 3 L hHCR shows visionary prospects in biosensing and the fabrication of advanced biocomputing networks.

Fluorescent labeled single-stranded DNA (ssDNA) molecules physisorbed on graphene oxide (GO) have been extensively explored as a useful sensing platform. However, this approach faces challenges when applied to complex biological samples due to heavy nonspecific desorption of nontarget molecules from GO. To overcome this problem, we introduced a capture DNA (cDNA) fragment with a poly adenine (poly-A) extension into the physisorption system that greatly reduces nonspecific desorption and false positive signal due to strong binding between poly-A and GO. Fluorescence from the dye can be effectively quenched by BHQ, which thus provides a second guarantee of anti-interference to avoid possible nonspecific poly-A DNA displacement. As a proof of concept, we have successfully developed a novel DNA-adsorbing GO nanocomplex probe (DNA-GO nanocomplex probe). This probe has a high anti-interference capability and low background due to the presence of both GO and black hole quencher (BHQ) as a dual-quencher that reduces the background in live cell imaging due to resonance energy transfer (RET). We then employed the DNA-GO nanocomplex probe for simultaneous detection of miR-630 and miR-21 and also for simultaneous in situ dynamic monitoring of intracellular miR-630 and miR-21 in apoptotic cells. We discovered that miR-630 expression was up-regulated during the first 120 min. This simple but powerful protocol has great potential in precise detection and imaging of various substances in complex biological samples with improved accuracy.

Plasmon resonance energy transfer (PRET), as a new form of energy transfer first discovered in 2007, has been widely applied for the biomolecular recognition, detection of ions, cellular physiological status monitoring, and energy conversion. It occurs between noble metal nanoparticles (donor) and conjugated molecules or nanoparticles (acceptor). In this study, we used urchin-like gold nanoplasmonics (UGPs) and

Owing to the sharp edge-enhanced electric field, gold triangular nanoplates (AuNPLs) exhibit strong localized surface plasmon resonance (LSPR) scattering and display as red spots with high intensity and narrow distribution under dark-field microscopy (DFM), based on which sensitive sensing applications could be developed. As a concept of proof, the inhibition effects of pyrophosphate (PPi) against the etching of AuNPLs based on Cu

Increasing demands for the sensitive, selective, visual, conveniently solid-phase-sensing film for disease-related biomarkers, electrospun nanofibrous films (ENFFs) are a novel sensing paltform because of the high surface area ratios, networked structures, and facile functionalization. In this research, carbon dots (CDs) and quantum dots (QDs) were doped inside and electrostatically assembled on electrospun nanofibers (ENFs), affording ratiometrically dual-emitting fluoresecent films. Because of the FRET process between CDs and QDs on NFs and the strong quenching response of QDs to Cu2+, the as-prepared NFs can visually detect Cu2+ with high sensitivity and selectivity based on ratiometric fluorescent signals. By exploiting the release of numerous Cu2+ from CuO nanoparticles (NPs) under acidic conditions, a sandwich-type immunoassay with CuO NPs-labeled antibody was developed for the detection of biomarker proteins via the response of dual-emitting and FRET-based NFs to different Cu2+ concentrations. Taki...