Ultrasensitive Electrochemiluminescence Detection of MicroRNA via One-Step Introduction of a Target-Triggered Branched Hybridization Chain Reaction Circuit

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

Identification of Iodine-Induced Morphological Transformation of Gold Nanorods

The morphological transformation process resulting from the reaction between Au nanorods (NRs) and iodine in situ produced from the redox between potassium iodide and copper chloride was monitored by virtue of the transmission electron microscope (TEM) images and the plasmon resonance absorption (PRA) spectra. It was found that the presence of copper chloride or potassium iodide could make the longitudinal PRA band of Au-NRs shift without any change of morphological transformation owing to the change of the refractive index of the medium. Different from that, iodine, which was in situ produced from the redox of potassium iodide and copper chloride, could fuse Au-NRs in the side-by-side mode, resulting in morphological transformation of Au-NRs to sphericity with the characteristics of the decrease of aspect ratio, blue-shift of the longitudinal PAR band, red-shift of transverse PRA band, and broadening of both longitudinal and transverse PRA bands of Au-NRs. The blue-shifted wavelength of the longitudinal PRA band was found to be in proportion to the concentration of copper chloride or potassium iodide when potassium iodide or copper chloride is sufficient, supplying the possibility to detect copper and iodine element in samples with spectrophotometry

Visual Sandwich Immunoassay System on the Basis of Plasmon Resonance Scattering Signals of Silver Nanoparticles

In this contribution, we established a sandwich immunoassay system with a common spectrofluorometer to collect the plasmon resonance scattering (PRS) signals from silver nanoparticles (AgNPs) immunotargeted on glass slides. By taking the immunoreactions of goat antihuman IgG (Fc fragment specific) antibody (GAH-IgG), human immunoglobulin (H-IgG), and rabbit antihuman IgG (Fab fragment specific) antibody (RAH-IgG) as an example, we found that if a primary antibody (GAH-IgG) was first immobilized on the surface of glass slides and applied to capture target antigen (H-IgG), AgNPs-labeled secondary antibody (RAH-IgG) could be employed to detect the target antigen (H-IgG) by forming a sandwich immune complex on the surface of the glass slide. It was found that the PRS signals resulting from the AgNPs immunotargeted on the glass slides could be applied to the quantitative detection of H-IgG target antigen in the range of 10−1000 ng/mL with the limit of determination of 1.46 ng/mL (3σ) under optimal conditions, which is sensitive and comparable with reported chemiluminescence immunoassays. With a dark-field microscope coupled with a spectral system, we measured the PRS features of single AgNPs immunotargeted on the glass slides, showing that the PRS of single nanoparticles might have potential applications in analytical chemistry. Further findings showed that the strong PRS signals from the AgNPs immunotargeted on the glass slides can be clearly seen and distinguished by naked eyes under the excitation of a common white light-emitting diode (LED) torch. Therefore, a visual PRS immunoassay system can be established easily with common glass slides and an LED torch

A One-Pot Green Method for One-Dimensional Assembly of Gold Nanoparticles with a Novel Chitosan−Ninhydrin Bioconjugate at Physiological Temperature

With our newly prepared novel chitosan−ninhydrin (CHIT-NH) bioconjugate in this contribution, we made one-dimensional (1-D) assemblies of gold nanoparticles (NPs) at physiological temperature. This 1-D assembly method is simple, one-pot, and totally green wherein multiplex functional groups of the CHIT-NH conjugate make the nonuniform spatial distribution of stabilizers to form organized 1-D assemblies. UV−vis and infrared spectroscopy have been employed for identifying the molecular structure of CHIT-NH conjugate, while scanning electron microscopy (SEM), transmission electron microscopy (TEM) for confirming the 1-D morphology of gold NP assemblies. Mechanism investigations on the basis of the measurements of dynamic light scattering (DLS), time-dependent optical spectra, visible observation on the change of solution color and SEM imaging showed that the CHIT-NH conjugate, a novel environmentally benign and excellently biocompatible material, serves not only as a reducing agent but also as a stabilizer for the growth and 1-D assembly of gold NPs

Fluorescence Assay Based on Preconcentration by a Self-Ordered Ring Using Berberine as a Model Analyte

A novel assay for trace amounts of fluorescent analytes is proposed based on the assembly of a self-ordered ring (SOR) through capillary flow in a sessile droplet on a glass slide support. After solvent evaporation of the sessile droplet containing a fluorescent analyte on a hydrophobic-treated glass slide, an outward capillary flow of the solvent from the interior of the droplet occurs. The resultant outward capillary flow then carries the analyte to the perimeter of the droplet spot where the analyte deposits and forms a fluorescent SOR. For the model analyte of berberine, SORs with outer diameter less than 1.2 mm and ring belt width less than 19 μm can be obtained depending on the droplet volume of the berberine solution. Data analysis for the digitally imaged SOR by using a CCD camera showed that the berberine molecules across the SOR belt section follow a Gaussian distribution, and the maximum fluorescent intensity (Imax) was found to be proportional to berberine content at the femtomole level. With the proposed technique, the content in tablets and the average excretion rates of berberine through human urine after oral administration could be satisfactorily monitored

Morphology Control and Structural Characterization of Au Crystals: From Twinned Tabular Crystals and Single-Crystalline Nanoplates to Multitwinned Decahedra

In this contribution, a general one-step route to synthesize Au crystals with the shape of twinned tabular crystals, single-crystalline nanoplates, and multitwinned decahedra is proposed. By employing HAuCl4 in an aqueous medium as the oxidizing reagent, tetracycline hydrochloride as the reducing agent, and cetyltrimethylammonium bromide (CTAB) as the capping agent, we found it is very easy to get the three types of Au crystals by modulating the molar ratio of CTAB with HAuCl4. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), and high-resolution TEM (HRTEM) have been employed to characterize the three types of symmetric morphologies. Further investigations involve side-face analysis and growth mechanism of Au twinned tabular crystals, and the optical properties of the obtained crystals. Absorption and dark field light scattering images demonstrate their potential applications in cancer cell diagnostics and photothermal therapy. Moreover, a tentative explanation for the growth mechanism of Au crystals with different morphologies has been made

Hybridization Detection of DNA by Measuring Organic Small Molecule Amplified Resonance Light Scattering Signals

The interaction of organic small molecules (OSMs) with a biological molecule is very important. In this contribution, quinone-imine dyes including Acridine Yellow (AY), Neutral Red (NR), Acridine Orange (AO), Brilliant Cresyl Blue (BCB), Thionin (TN), Azur A (AA), Azur B (AB), and Methylene Blue (MB) respectively with double strand DNA (dsDNA) and single strand DNA (ssDNA) were investigated based on the measurements of enhanced resonance light scattering (RLS) and TEM. Mechanism investigations have shown that groove binding occurs between dsDNA and these OSMs, which depends on G-C sequences of dsDNA and the volumes of OSMs. With the amplified RLS signals resulting from the interactions of OSMs with DNA, a new technique has been proposed to detect the hybridization and mismatch of DNA labeling neither the target nor the probe DNA. The results have suggested that the extent of the amplified RLS signals of dsDNA by AY is the maximum among these eight OSMs, and therefore, it has been selected as a typical model system for further discussions

Total Internal Reflected Resonance Light Scattering Determination of Chlortetracycline in Body Fluid with the Complex Cation of Chlortetracycline−Europium−Trioctyl Phosphine Oxide at the Water/Tetrachloromethane Interface

A highly selective method of chlortetracycline (CTC) is proposed on the basis of the measurements of total internal reflected resonance light scattering (TIR-RLS) at water/tetrachloromethane (H2O/CCl4) interfaces. In the pH range of 7.54−8.14, the interaction of the binary complex of Eu(III)/CTC in the presence of trioctyl phosphine oxide (TOPO) occurs at the H2O/CCl4 interface, resulting in greatly enhanced TIR-RLS signals with the maximum peak located at 340 nm. The enhanced TIR-RLS intensity is in proportion to the CTC concentration in the range 0.98∼20.0 × 10-7 mol/L. The limit of detection is 9.8 × 10-9 mol/L. Synthetic samples and body fluid samples including human urine, human serum, and fresh milk were determined with the recovery of 95.4−106.4% and RSD of 2.9−3.9%

Silver Nanocubes Formed on ATP-Mediated Nafion Film and a Visual Method for Formaldehyde

The ability to construct size- and shape-controllable architectures is essential for the exploration of nanoparticle-structured properties, and it is a good strategy of employing metal nanoparticles embedded in a polymer matrix in order to prepare new materials with particular properties. Herein, we found that adenosine-5′-triphosphate (ATP) could be applied to adjust and control the formation of silver nanocubes (Ag-NCs) on Nafion film. Nafion could be saturated with [Ag(NH3)2]+ when incubated in silver ammonia solution, and it was found that the Nafion film saturated with [Ag(NH3)2]+ becomes yellow after immerged in a mixture containing NaOH, ATP, and formaldehyde, resulting in monodisperse Ag-NCs on the film. Thus, ATP as a molecular mediator and Nafion film as a polymer matrix are employed toward the preparation of size-controllable and monodisperse Ag-NCs, and a novel visual method for formaldehyde is further developed on the basis of the color change of the Nafion film, which gives sensitive detection of formaldehyde with a limit of determination of 60 ppb (3σ)

Visual Detection of Sudan Dyes Based on the Plasmon Resonance Light Scattering Signals of Silver Nanoparticles

A visual light scattering detection method of Sudan dyes is reported in food products based on the formation of silver nanoparticles (NPs) . Sudan dyes including I, II, III and IV have reducibility due to the nitrogen−nitrogen double bond and phenol group in their molecular structure, and a redox reaction could occur with AgNO3. Owing to the formation of silver NPs as a result of the redox reaction, color changes could be observed by eye from the red of Sudan to the brown of silver NPs, resulting in strong plasmon resonance light scattering (PRLS) signals characterized at 452 nm, which could be measured using a common spectrofluorometer. It was found that the PRLS intensities were proportional to the dye concentrations over the range of 0.2−2.4 μM Sudan I, 0.1−2.4 μM Sudan II, 0.1−2.4 μM Sudan III, and 0.2−3.0 μM Sudan IV, with the corresponding limits of determination (3σ) of 3.2, 3.0, 3.2, and 2.9 nM, respectively. Using hot chili as a model sample, detection could be made with the recovery of 90.8−103.3% and RSD of 4.0−4.9%, and the results are identical with that of a liquid chromatographic method approved by the European Commission. To make the PRLS method much more practical, we could visually detect the quantity of Sudan dyes based on the PRLS signals using simple devices such as a portable laser pointer (653 nm) and a light emitting diode (458 nm). Mechanism investigations show that the functional group of Sudan oxidized by AgNO3 is the phenol group, not the nitrogen−nitrogen double bond