A novel silver nanocluster in situ synthesized as versatile probe for electrochemiluminescence and electrochemical detection of thrombin by multiple signal amplification strategy

Homogeneous electrochemical aptasensor for mucin 1 detection based on exonuclease I-assisted target recycling amplification strategy

A sensitive and homogeneous electrochemical aptasensor was fabricated for the detection of mucin 1 (MUC1) by combining a well-designed DNA bulge-loop (L-DNA) structure with high-efficient exonuclease I (Exo I)-assisted target recycling amplification strategy. The L-DNA probe was constructed via the hybridization of the MUC1 aptamer and methylene blue (MB) labeled complementary DNA (cDNA) (cDNA-MB) and hence could not diffuse freely to the negatively charged ITO electrode surface due to the strong electrostatic repulsion, so small electrochemical signal was detected. The addition of MUC1 caused the dissociation of L-DNA structure due to the specificity between aptamer and MUC1. Then Exo I was implemented to digest the released cDNA-MB into mononucleotides and then produced short MB-labeled mononucleotides fragments (MB-MFs). As the MB-MFs contained few negative charges, it diffused easily to the negatively charged ITO electrode surface and resulted in the enhanced electrochemical signal. Meanwhile, the MUC1-aptamer complex was also specifically digested by Exo I, resulting in the liberation of MUC1 and hence realized the target recycling and then caused the amplification of the electrochemical signal. The enhanced electrochemical signal has a good linear relationship with logarithm of MUC1 concentration in the range of 1.0 pg mL^-1-50 ng mL^-1 with a limit of detection of 0.40 pg mL^-1 (S/N = 3). Additionally, the fabricated aptasensor has been successfully applied to detect MUC1 in serum samples with satisfactory results and thereby it exhibits great potential in the practical application of clinical diagnosis.

An electrochemiluminescence biosensor for detection of CdkN2A/p16 anti-oncogene based on functional electrospun nanofibers and core-shell luminescent composite nanoparticles

An electrochemiluminescence (ECL) biosensor based on functional electrospun nanofibers for hybridization detection of specific CdkN2A/p16 anti-oncogene at trace level via binding luminescent composite nanoparticles for signal amplification has been developed. The carboxylated multiwalled carbon nanotubes (MWCNTs) doped polycaprolactam 6 (PA6) electrospun nanofibers (PA6-MWCNTs) was prepared via electrospinning, which served as the nanosized backbones for silica nanoparticles (SiO₂) electrodeposition. The functional electrospun nanofibers (PA6-MWCNTs-SiO₂) used as supporting scaffolds for single-stranded DNA1 (ssDNA1) immobilization can dramatically increase the amount of DNA attachment and the sensitivity of hybridization. The sandwich construction of ssDNA1-CdkN2A/p16 anti-oncogene -tri(2,2'-bipyridyl)ruthenium(II) (Ru(bpy)₃²⁺)/silver nanoparticles (AgNPs) doped gold (Au) core-shell luminescent composite nanoparticles (RuAg@AuNPs)-labeled ssDNA2 (RuAg@Au-ssDNA2) was fabricated through a hybridization reaction. It was observed that high amount of doped Ru(bpy)₃²⁺ in RuAg@AuNPs successfully amplify the recognition signal by adding tripropylamine (TPrA). The change of ECL intensity was found to have a linear relationship in respect to the logarithm of the CdkN2A/p16 anti-oncogene concentrations in the wide range of 1.0 × 10^-15~1.0 × 10^-12 M, with a detection limit of 0.5 fM (S/N = 3) which is comparable or better than that in reported anti-oncogene assays. Excellent sensitivity and selectivity make the developed biosensor a promising tool for the detection of tumor biomarkers.

Promising Anodic Electrochemiluminescence of Nontoxic Core/Shell CuInS2/ZnS Nanocrystals in Aqueous Medium and Its Biosensing Potential

Copper indium sulfide (CuInS₂, CIS) nanocrystals (NCs) are a promising solution to the toxic issue of Cd- and Pb-based NCs. Herein, electrochemiluminescence (ECL) of CIS NCs in aqueous medium is investigated for the first time with l-glutathione and sodium citrate-stabilized water-soluble CIS/ZnS NCs as model. The CIS/ZnS NCs can be oxidized to hole-injected states via electrochemically injecting holes into valence band at 0.55 and 0.94 V (vs Ag/AgCl), respectively. The hole-injected state around 0.94 V can bring out efficient oxidative-reduction ECL with a similar color to Ru(bpy)₃²⁺ in the presence of tri- n-propylamine (TPrA) and enable CIS/ZnS NCs promising ECL tags with l-glutathione as linker for labeling. The ECL of CIS/ZnS NCs/TPrA can be utilized to determine vascular endothelial growth factor (VEGF) from 0.10 to 1000 pM with the limit of detection at 0.050 pM (S/N = 3). Although the hole-injected state around 0.55 V is generated ahead of oxidation of TPrA and fails to bring out coreactant ECL, annihilation ECL proves that both hole-injected states generated, at 0.55 and 0.94 V, can be involved in electrochemical redox-induced radiative charge transfer by directly stepping CIS/ZnS NCs from electron-injecting potential to hole-injecting potential. CIS/ZnS NCs are promising nontoxic electrochemiluminophores with lowered ECL triggering potential around 0.55 V for less electrochemical interference upon the development of coreactant.

Optical nano-biosensing interface via nucleic acid amplification strategy: construction and application

Modern optical detection technology plays a critical role in current clinical detection due to its high sensitivity and accuracy. However, higher requirements such as extremely high detection sensitivity have been put forward due to the clinical needs for the early finding and diagnosing of malignant tumors which are significant for tumor therapy. The technology of isothermal amplification with nucleic acids opens up avenues for meeting this requirement. Recent reports have shown that a nucleic acid amplification-assisted modern optical sensing interface has achieved satisfactory sensitivity and accuracy, high speed and specificity. Compared with isothermal amplification technology designed to work completely in a solution system, solid biosensing interfaces demonstrated better performances in stability and sensitivity due to their ease of separation from the reaction mixture and the better signal transduction on these optical nano-biosensing interfaces. Also the flexibility and designability during the construction of these nano-biosensing interfaces provided a promising research topic for the ultrasensitive detection of cancer diseases. In this review, we describe the construction of the burgeoning number of optical nano-biosensing interfaces assisted by a nucleic acid amplification strategy, and provide insightful views on: (1) approaches to the smart fabrication of an optical nano-biosensing interface, (2) biosensing mechanisms via the nucleic acid amplification method, (3) the newest strategies and future perspectives.

An electrochemical biosensor for microRNA-196a detection based on cyclic enzymatic signal amplification and template-free DNA extension reaction with the adsorption of methylene blue

A simple and sensitive electrochemical biosensor was developed for microRNA-196a detection, which is of important diagnostic significance for pancreatic cancer. It was based on cyclic enzymatic signal amplification (CESA) and template-free DNA extension reaction. In the presence of microRNA-196a, duplex-specific nuclease (DSN) catalyzed the digestion of the 3'-PO₄ terminated capture probe (CP), resulting in the target recycling amplification. Meanwhile, the 3'-OH terminal of CP was exposed. Then, template-free DNA extension reaction was triggered by terminal deoxynucleotidyl transferase (TdT), producing amounts of single-stranded DNA (ssDNA). After ssDNA absorbed numerous methylene blue (MB), an ultrasensitive electrochemical readout was obtained. Based on this dual amplification mechanism, the proposed biosensor exhibited a high sensitivity for detection of microRNA-196a down to 15 aM with a linear range from 0.05 fM to 50 pM. This biosensor displayed high specificity, which could discriminate target microRNAs from one base mismatched microRNAs. It also showed good reproducibility and stability. Furthermore, it was successfully applied to the determination of microRNA-196a in plasma samples. In conclusion, with the excellent analytical performance, this biosensor might have the potential for application in clinical diagnostics of pancreatic cancer.

Label-free and nicking enzyme-assisted fluorescence signal amplification for RNase H determination based on a G-quadruplexe/thioflavin T complex

In this paper, we describe a novel, label-free and nicking enzyme-assisted fluorescence signal amplification strategy that demonstrates to be cost efficient, sensitive, and unique for assaying the RNase H activity and inhibition based on G-quadruplex formation using a thioflavin T (ThT) dye. This novel assay method is able to detect RNase H with a detection limit of 0.03 U /mL and further exhibits a good linearity R² = 0.9923 at a concentration range of 0.03-1 U/mL under optimized conditions. Moreover, the inhibition effect of gentamycin on the RNase H activity is also studied. This strategy provides a potential tool for the biochemical enzyme analysis and inhibitor screening.

A turn-on fluorescence assay of alkaline phosphatase activity using a DNA–silver nanocluster probe

A label-free fluorescence assay has been developed for the detection of alkaline phosphatase based on DNA–silver nanocluster probes.

Electrochemiluminescent resonance energy transfer of polymer dots for aptasensing

This work designed a three-component polymer for the preparation of polymer dots (Pdots). The polymer contained 9-(diphenylmethylene)-9H-fluorene (DPF), 9,9-dioctyl-9H-fluorene (DOF) and 1,1'-binaphthyl moieties, and was synthesized via Pd-catalyzed Suzuki reaction. It exhibited obvious yellow-colored aggregation-induced emission (AIE) for fluorescence enhancement at 543nm via an intramolecular fluorescence resonance energy transfer from DOF moiety to DPF moiety. The Pdots prepared by nanoprecipitation could be conveniently cast on electrode surface and showed a stable anodic electrochemiluminescence (ECL) emission in the presence of triethylamine as a co-reactant. The ECL emission could be effectively quenched by rhodamine B via resonance energy transfer, which led to an "off-on" switch for the design of ECL sensing methodology. Using Pb²⁺ as a target model, an ECL aptasensor for the detection of trace Pb²⁺ was proposed, which showed a linear range of 100pM to 1.0μM with a detection limit down to 38.0pM This work demonstrated the first Pdots prepared with AIE-active polymer for highly efficient ECL sensing.