Herein, by directly using Watson–Crick base pairing, a highly ordered and field-free three-dimensional (3D) DNA nanostructure is self-assembled by azobenzene (azo)-functionalized DNA nippers in a few ...minutes, which was applied as a 3D DNA nanomachine with an improved movement efficiency compared to traditional Au-based 3D nanomachines due to the organized and high local concentration of nippers on homogeneous DNA nanostructure. Once microRNA (miRNA) interacts with the 3D nanomachine, the nippers “open” to hybridize with the miRNA. Impressively, photoisomerization of the azo group induces dehybridization/hybridization of the nippers and miRNA under irradiation at different wavelengths, which easily solves one main technical challenge of DNA nanotechnology and biosensing: reversible locomotion in one step within 10 min. As a proof of concept, the described 3D machine is successfully applied in the rapid single-step detection of a biomarker, which gives impetus to the design of new generations of mechanical devices beyond the traditional ones with ultimate applications in sensing analysis and diagnostic technologies.
In situ monitoring of hydrogen peroxide (H2O2) secreted from live cells plays a critical role in elucidating many cellular signaling pathways, and it is a significant challenge to selectively detect ...these low levels of endogenous H2O2. To address this challenge, we report the establishment of a trimetallic hybrid nanoflower-decorated MoS2 nanosheet-modified sensor for in situ monitoring of H2O2 secreted from live MCF-7 cancer cells. The Au–Pd–Pt nanoflower-dispersed MoS2 nanosheets are synthesized by a simple wet-chemistry method, and the resulting nanosheet composites exhibit significantly enhanced catalytic activity toward electrochemical reduction of H2O2, due to the synergistic effect of the highly dispersed trimetallic hybrid nanoflowers and the MoS2 nanosheets, thereby resulting in ultrasensitive detection of H2O2 with a subnanomolar level detection limit in vitro. Also the immobilization of the laminin glycoproteins on the surface of the nanocomposites increases its biocompatibility for cell adhesion and growth, which enables in situ electrochemical monitoring of H2O2 directly secreted from live cells for potential application of such sensor in cellular biology, clinical diagnosis, and pathophysiology.
Reliable and sensitive in situ detection of molecules released from live cells attracts tremendous research interest, as it shows significance in pathological and physiological investigation. In the ...present work, a novel electrochemiluminescent (ECL) luminophore, N-(aminobutyl)-N-(ethylisoluminol)-functionalized Ag nanoparticles modified three-dimensional (3D) polyaniline–phytic acid conducting hydrogel (ABEI–Ag@PAni–PA), is synthesized to adhere cells for in situ sensitive ECL detection of hydrogen peroxide (H2O2) released from live cells. The obtained 3D nanostructured ABEI–Ag@PAni–PA conducting hydrogels synergize the advantages of a conducting hydrogel and a nanoparticle catalyst, in which the PAni–PA conducting hydrogels benefit the cell adhesion and high loading density of the ABEI–Ag luminescent material due to their good biocompatibility, porous structure, and 3D continuous framework. Importantly, compared with the traditional procedure for detection of H2O2 released from cells in solution, adhesion of cells on ABEI–Ag@PAni–PA conducting hydrogels provides a short diffusion distance to reaction sites for H2O2, thus realizing sensitive in situ monitoring of H2O2 released from cells under drug stimulation. With good biocompatibility, high sensitivity, and easy preparation, the ECL biosensor based on ABEI–Ag@PAni–PA conducting hydrogels can be expanded to detect other molecules released from cells, which may facilitate the investigation of pathology and physiology.
Generally, electrochemiluminescence (ECL) ratiometric assays were based on the energy transfer (ET) between an emitter and a metal nanomaterial or between two different emitters. The choice of ...suitable energy donor–acceptor pair and the distance dependence of ET would greatly limit the practical application of ratiometric assays. This work explored a novel double-potential ECL ratiometry without the ET for organophosphorus pesticides (OPs) analysis, in which, reduced graphene oxide-CdTe quantum dots (RGO-CdTe QDs) and carboxyl-conjugated polymer dots (PFO dots) were chosen as cathodic and anodic ECL emitters, and the reactant (dissolved O2) and the product (H2O2) in enzymatic reactions served as their coreactants, respectively. With the occurrence of the enzymatic reactions induced by the acetylcholinesterase (AChE) and choline oxidase (ChOx), the cathodic ECL signal from RGO-CdTe QDs was at “signal off” state due to the consumption of dissolved O2. Meanwhile, the anodic ECL signal from PFO dots was at “signal on” state due to the in situ generation of H2O2. In the presence of OPs, the cathodic ECL signal would increase while the anodic ECL signal would decline correspondingly due to the inhibition of OPs on the activity of AChE. Using the reactant and the product in enzymatic reactions as the coreactants of two different ECL emitters, we conveniently achieved the opposite change trend in two ECL signals for the ratiometric detection of OPs, which exhibited a greatly improved accuracy, reliability and sensitivity, thus, showing a great attraction for developing ECL ratiometric systems for the bioanalysis.
Herein, a dual microRNA (miRNA) powered bi-directional DNA walking machine with precise control was developed to fabricate an enzyme-free biosensor on the basis of distance-based ...electrochemiluminescence (ECL) energy transfer for multiple detection of miRNAs. By using miRNA-21 as the driving force, the DNA walker could move forth along the track and generated quenching of ECL response due to the proximity between Au nanoparticles (AuNPs) and Mn2+ doped CdS nanocrystals (CdS:Mn NCs) film as the ECL emitters, realizing ultrasensitive determination of miRNA-21. Impressively, once miRNA-155 was introduced as the driving force, the walker could move back along the track automatically, and surface plasmon resonance (SPR) occurred owing to the appropriate large separation between AuNPs and CdS:Mn NCs, achieving an ECL enhancement and realizing ultrasensitive detection of miRNA-155. The bi-directional movement of the DNA walker on the track led to continuous distance-based energy transfer from CdS:Mn NCs film by AuNPs, which resulted in significant ECL signal variation of CdS:Mn NCs for multiple detection of miRNA-21 and miRNA-155 down to 1.51 fM and 1.67 fM, respectively. Amazingly, the elaborated biosensor provided a new chance for constructing controllable molecular nanomachines in biosensing, disease diagnosis, and clinical analysis.
The detection of specific intracellular microRNAs (miRNAs) in living cells can potentially provide insight into the causal mechanism of cancer metastasis and invasion. However, because of the ...characteristic nature of miRNAs in terms of small sizes, low abundance, and similarity among family members, it is a great challenge to monitor miRNAs in living cells, especially those with much lower expression levels. In this work, we describe the establishment of a DNA-fueled and catalytic molecule machinery in cell signal amplification approach for monitoring trace and under-expressed miRNAs in living cells. The presence of the target miRNA releases the hairpin sequences from the dsDNA (containing the fluorescence resonance energy transfer (FRET) pair-labeled and unfolded hairpin sequences)-conjugated gold nanoparticles (dsDNA-AuNPs), and the DNA fuel strands assist the recycling of the target miRNA sequences via two cascaded strand displacement reactions, leading to the operation of the molecular machine in a catalytic fashion and the release of many hairpin sequences. As a result, the liberated hairpin sequences restore the folded hairpin structures and bring the FRET pair into close proximity to generate significantly amplified signals for detecting trace miRNA targets. Besides, the dsDNA-AuNP nanoprobes have good nuclease stability and show low cytotoxicity to cells, and the application of such a molecular system for monitoring trace and under-expressed miRNAs in living cells has also been demonstrated. With the advantages of in cell signal amplification and reduced background noise, the developed method thus offers new opportunities for detecting various trace intracellular miRNA species.
On the basis of a novel target-cycling synchronized rolling circle amplification (RCA) as a signal amplification strategy and in situ electrochemical generation of silver nanoclusters (Ag NCs) as ...signal probes, an ultrasensitive and simple electrochemiluminescence (ECL) biosensor was proposed for microRNA (miRNA) detection. It was worth mentioning that the circular template was subtly designed to consist of a guanine-rich (G-rich) region and a binding region for realizing target-cycling synchronized RCA. In the presence of target miR-21, the binding region hybridized with the primer and the target miR-21 to form a ternary “P” junction structure, and then the RCA was triggered from the 3′-end of the primer. Along with the proceeding of RCA, the target miR-21 was released and participated into another trigger of the RCA. On account of the G-rich region in the circular template, the product DNA of the target-cycling synchronized RCA possessed tandem periodic cytosine-rich (C-rich) sequences, which acted as ligands to further in situ electrochemically generate silver nanoclusters (Ag NCs) as ECL signal probes. As expected, the obtained ECL intensity dependent on the amount of the Ag NCs, which was positively related to the concentration of the target miR-21. The ECL assay for miR-21 detection demonstrated excellent linear response to a concentration variation from 100 aM to 100 pM and limit of detection down to 22 aM.
The preparation of self-assembled DNA nanostructure with different sizes and shapes has been one of the most promising research areas in recent years, while the application of these DNA ...nanostructures in biosensors is far from fully developed. Here, we presented a novel carrier system to construct an electrochemiluminescence (ECL) aptasensor for ultrasensitive determination of lipopolysaccharides (LPS) on the basis of self-assembled tetrahedron DNA dendrimers. Doxorubicin (Dox), a well-known intercalator of double stranded DNA (dsDNA), was conjugated with the ECL luminophore of N-(aminobutyl)-N-(ethylisoluminol) (ABEI) to form a new type of ECL indicators (Dox-ABEI), which could noncovalently attach to dsDNA through intercalation. Based on this property, self-assembled tetrahedron DNA dendrimers were employed as an efficient nanocarrier to achieve a high loading efficiency for Dox-ABEI with significantly amplified ECL signal output. Streptavidin (SA) and biotin, a typical ligand–receptor pair, has been chosen to anchor the tetrahedron DNA dendrimers on the electrode surface. Moreover, by converting LPS content into DNA output, catalyzed hairpin assembly (CHA) target recycling signal amplification strategy was also adopted to enhance the sensitivity of the ECL aptasensor. With combining the loading power of the tetrahedron DNA dendrimers for ECL indicators, the inherent high sensitivity of ECL technique and target recycling for signal amplification, the proposed strategy showed a detection limit of 0.18 fg/mL for LPS.
A novel ratiometric surface-enhanced Raman scattering (SERS) biosensor was constructed based on stimuli-responsive DNA functionalized metal organic frameworks (MOFs) for detection of adenosine ...triphosphate (ATP). As a result, the detection range of ATP was 1 nM to 200 nM with a detection limit of 0.4 nM. The ratiometric SERS biosensor strategy offers a lower detection limit and exhibits a more enhanced performance than the typical SERS detection based on single signal response, which may have potential for detection of other biomolecules or metal ions.
In this work, a ferrocene (Fc)-driven light switch biosensor for ultrasensitive detection of amyloid-β (Aβ) was designed by utilizing the highly efficient electrochemiluminescent nanomaterials of ...silver nanoclusters/titanium oxide nanoflowers (Ag NCs/TiO2 NFs) as signal labels. Through combining the TiO2 NFs as the coreaction accelerator and dissolved O2 as the intrinsic coreactant to in situ generate the strong oxidizing intermediate radical OH•, the electrochemiluminescence (ECL) of Ag NCs on the TiO2 NFs surface could be significantly promoted in comparison with that of pure Ag NCs in solution. Further, Fc-labeled DNA as the ECL quenching probe was introduced to dramatically restrain the ECL emission of nanomaterials, which facilitated improving the sensitivity of the prepared biosensor to a large extent. Surprisingly, tiny amounts of target protein could be recognized by the immunoreaction-induced DNA nanostructure for outputting numerous secondary-target DNAs, which further triggered the release of Fc to recover the ECL signal, realizing the ultrasensitive detection of target. As a result, this developed assay for Aβ detection demonstrated excellent sensitivity with a linear range from 50 fg/mL to 500 ng/mL and limit of detection down to 32 fg/mL, which opened up a new research direction for ultrasensitive ECL bioanalysis-based metal NCs.
