Thy-AuNP-AgNP Hybrid Systems for Colorimetric Determination of Copper (II) Ions Using UV-Vis Spectroscopy and Smartphone-Based Detection

A colorimetric probe based on a hybrid sensing system of gold nanoparticles (AuNPs), silver nanoparticles (AgNPs), and thymine (Thy) was developed for easy and rapid detection of copper (II) ions (Cu2+) in solution. The underlying principle of this probe was the Cu2+-triggered aggregation of the nanoparticle components. Color change of the sensing solution (from red to purple) was clearly observed with naked eyes. The experimental parameters, including pH and concentration of tris buffer, thymine concentration and AgNP dilution ratios, were investigated and optimized. Once optimized, the limits of detection were found to be 1, 0.09 and 0.03 ppm for naked eyes, smartphone application and UV-vis spectrophotometer, respectively. Furthermore, determination of Cu2+ was accomplished within 15 min under ambient conditions. For quantitative analysis, the linearity of detection was observed through ranges of 0.09−0.5 and 0.03−0.5 ppm using smartphone application and UV-vis spectrophotometer, respectively, conforming to the World Health Organization guideline for detection of copper at concentrations < 2 ppm in water. This developed hybrid colorimetric probe exhibited preferential selectivity toward Cu2+, even when assessed in the presence of other metal ions (Al3+, Ca2+, Pb2+, Mn2+, Mg2+, Zn2+, Fe3+, Ni2+, Co2+, Hg2+ and Cd2+). The developed procedure was also successfully applied to quantification of Cu2+ in real water samples. The recovery and relative standard deviation (RSD) values from real water sample analysis were in the ranges of 70.14−103.59 and 3.21−17.63%, respectively. Our findings demonstrated a successful development and implementation of the Thy-AuNP-AgNP hybrid sensing system for rapid, simple and portable Cu2+ detection in water samples using a spectrophotometer or a smartphone-based device.

In Vivo Chemoselective Photoacoustic Imaging of Copper(II) in Plant and Animal Subjects

The detection of Cu2+ in living plants and animals is of great importance for environment monitoring and disease diagnosis. Here, a near-infrared (NIR) turn-on photoacoustic (PA) probe (denoted as LET-2) is developed for Cu2+ detection in living subjects, such as soybean sprouts and mice. The absorbance band of LET-2 shifts from 625 to 715 nm after the interaction with Cu2+ , thus producing strong PA signal output at 715 nm (PA715 ) as an indicator. The PA715 value is increased as a function of the concentration of Cu2+ (0 × 10-6 -20 × 10-6 m), with a calculated limit of detection of 10.8 × 10-9 m. More importantly, both in vitro and in vivo studies in soybean sprouts and mice indicate that the as-prepared LET-2 PA probe is highly sensitive and selective for Cu2+ detection. These findings provide a solution for in vivo detection of metal ions by using chemoselective PA probes.

Dual enzyme-free amplification strategy for ultra-sensitive fluorescent detection of bisphenol A in water

An ultra-sensitive strategy for bisphenol A (BPA) detection based on dual enzyme-free strategies: hybridization chain reaction (HCR) and enzyme-strand recycling reaction has been developed. The BPA aptamer can form hairpins structure by the partly self-complementary sequence. In the presence of BPA, the released BPA aptamer sequence can trigger the HCR between two hairpins to from a long nicked double-helix DNA. The tails of hairpins on the duplex DNA were closely enough to hybridize with molecular beacon (MB) on the gold nanoparticles (AuNPs) to circularly cleave the loop of MB, leading to a "turn-on" fluorescent signal. This method exhibited high sensitivity for BPA detection in a linear rang from 0.2 to 1000 pM with 0.05 pM of limit of detection. Moreover, it was successfully used for BPA detection in real water samples. Importantly, this method was simple without complex enzymatic procedure and high cost, showing a promising future for on-site detection of BPA in practical application.

Recent applications of click chemistry for the functionalization of gold nanoparticles and their conversion to glyco-gold nanoparticles

Glycoscience, despite its myriad of challenges, promises to unravel the causes of, potential new detection methods for, and novel therapeutic strategies against, many disease states. In the last two decades, glyco-gold nanoparticles have emerged as one of several potential new tools for glycoscientists. Glyco-gold nanoparticles consist of the unique structural combination of a gold nanoparticle core and an outer-shell comprising multivalent presentation of carbohydrates. The combination of the distinctive physicochemical properties of the gold core and the biological function/activity of the carbohydrates makes glyco-gold nanoparticles a valuable tool in glycoscience. In this review we present recent advances made in the use of one type of click chemistry, namely the azide-alkyne Huisgen cycloaddition, for the functionalization of gold nanoparticles and their conversion to glyco-gold nanoparticles.

Ultra-facile and rapid colorimetric detection of Cu2+ with branched polyethylenimine in 100% aqueous solution

An ultra-facile and rapid colorimetric method was explored to detect Cu²⁺ in 100% aqueous solution by using only BPEI.

A novel carbon quantum dot-based fluorescent nanosensor for selective detection of flumioxazin in real samples

Herein, a carbon quantum dot-based highly selective luminescent probe has been designed for the detection of the pesticide flumioxazinviathe alkyne azide click reaction.

Materials for Microfluidic Immunoassays: A Review

Conventional immunoassays suffer from at least one of these following limitations: long processing time, high costs, poor user-friendliness, technical complexity, poor sensitivity and specificity. Microfluidics, a technology characterized by the engineered manipulation of fluids in channels with characteristic lengthscale of tens of micrometers, has shown considerable promise for improving immunoassays that could overcome these limitations in medical diagnostics and biology research. The combination of microfluidics and immunoassay can detect biomarkers with faster assay time, reduced volumes of reagents, lower power requirements, and higher levels of integration and automation compared to traditional approaches. This review focuses on the materials-related aspects of the recent advances in microfluidics-based immunoassays for point-of-care (POC) diagnostics of biomarkers. We compare the materials for microfluidic chips fabrication in five aspects: fabrication, integration, function, modification and cost, and describe their advantages and drawbacks. In addition, we review materials for modifying antibodies to improve the performance of the reaction of immunoassay. We also review the state of the art in microfluidic immunoassays POC platforms, from the laboratory to routine clinical practice, and also commercial products in the market. Finally, we discuss the current challenges and future developments in microfluidic immunoassays.

Two-Way Gold Nanoparticle Label-Free Sensing of Specific Sequence and Small Molecule Targets Using Switchable Concatemers

A two-way colorimetric biosensor based on unmodified gold nanoparticles (GNPs) and a switchable double-stranded DNA (dsDNA) concatemer have been demonstrated. Two hairpin probes (H1 and H2) were first designed that provided the fuels to assemble the dsDNA concatemers via hybridization chain reaction (HCR). A functional hairpin (FH) was rationally designed to recognize the target sequences. All the hairpins contained a single-stranded DNA (ssDNA) loop and sticky end to prevent GNPs from salt-induced aggregation. In the presence of target sequence, the capture probe blocked in the FH recognizes the target to form a duplex DNA, which causes the release of the initiator probe by FH conformational change. This process then starts the alternate-opening of H1 and H2 through HCR, and dsDNA concatemers grow from the target sequence. As a result, unmodified GNPs undergo salt-induced aggregation because the formed dsDNA concatemers are stiffer and provide less stabilization. A light purple-to-blue color variation was observed in the bulk solution, termed the light-off sensing way. Furthermore, H1 ingeniously inserted an aptamer sequence to generate dsDNA concatemers with multiple small molecule binding sites. In the presence of small molecule targets, concatemers can be disassembled into mixtures with ssDNA sticky ends. A blue-to-purple reverse color variation was observed due to the regeneration of the ssDNA, termed the light-on way. The two-way biosensor can detect both nucleic acids and small molecule targets with one sensing device. This switchable sensing element is label-free, enzyme-free, and sophisticated-instrumentation-free. The detection limits of both targets were below nanomolar.

Chloride accelerated Fenton chemistry for the ultrasensitive and selective colorimetric detection of copper

A highly selective, ultrasensitive (visual and instrumental detection limits of 40 nM and 0.1 nM, respectively), environmentally-friendly, simple and rapid colorimetric sensor was developed for the detection of copper(II) in water. This sensor is based on a novel signal-amplification mechanism involving reactive halide species (RHSs) including chlorides or bromides, which accelerate copper Fenton reactions oxidizing the chromogenic substrate to develop colour. The results of this study expand our understanding of copper-based Fenton chemistry.

Detection of the nanomolar level of total Cr[(iii) and (vi)] by functionalized gold nanoparticles and a smartphone with the assistance of theoretical calculation models

We report a method for rapid, effective detection of both Cr(iii) and Cr(vi) (in the form of Cr(3+) and Cr2O7(2-), the main species of chromium in the natural environment) by making use of meso-2,3-dimercaptosuccinic acid (DMSA)-functionalized gold nanoparticles (Au NPs). The limit of detection (LOD) is 10 nM with the naked eye and the assay can be applied in detecting chromium in polluted soil from Yun-Nan Province in Southwest China. We use density functional theory to calculate the change of the Gibbs free energy (ΔG) of the interactions between the DMSA-Au NP system and various metal ions, which shows that DMSA-Au NPs have high specificity for both Cr(3+) and Cr2O7(2-).

Coupling a novel spiro-rhodamine B lactam derivative to Fe3O4 nanoparticles for visual detection of free copper ions with high sensitivity and specificity

A novel spiro-rhodamine B lactam derivative, which can be coupled to Fe₃O₄ NPs and act as a Cu²⁺-selective visual sensor is reported. It can be used to directly detect as little as 50 nM of Cu²⁺ in river or tap water by only naked-eye observation.

Click chemistry-mediated catalytic hairpin self-assembly for amplified and sensitive fluorescence detection of Cu2+in human serum

Cu⁺-mediated click ligation of DNA leads to catalytic self-assembly of hairpins and amplified fluorescent signals for sensitive detection of Cu²⁺.

Effect of latent heat in boiling water on the synthesis of gold nanoparticles of different sizes by using the Turkevich method

The Turkevich method, involving the reduction of HAuCl4 with citrate in boiling water, allows the facile production of monodisperse, quasispherical gold nanoparticles (AuNPs). Although, it is well-known that the size of the AuNPs obtained with the same recipe vary slightly (as little as approximately 4 nm), but noticeably, from one report to another, it has rarely been studied. The present work demonstrates that this size variation can be reconciled by the small, but noticeable, effect that the latent heat in boiling water has on the size of the AuNPs obtained by using the Turkevich method. The increase in latent heat during water boiling caused an approximately 3 nm reduction in the size of the as-prepared AuNPs; this reduction in size is mainly a result of accelerated nucleation driven by the extra heat. It was further demonstrated that, the heating temperature can be utilized as an additional measure to adjust the growth rate of AuNPs during the reduction of HAuCl4 with citrate in boiling water. Therefore, the latent heat of boiling solvents may provide one way to control nucleation and growth in the synthesis of monodisperse nanoparticles.

A ligation DNAzyme-induced magnetic nanoparticles assembly for ultrasensitive detection of copper ions

A novel biosensor for ultrasensitive detection of copper (Cu(2+)) was established based on the assembly of magnetic nanoparticles induced by the Cu(2+)-dependent ligation DNAzyme. With a low limit of detection of 2.8 nM and high specificity, this method has the potential to serve as a general platform for the detection of heavy metal ions.

Two-photon ratiometric fluorescent sensor based on specific biomolecular recognition for selective and sensitive detection of copper ions in live cells

In this work, we develop a ratiometric two-photon fluorescent probe, ATD@QD-E2Zn2SOD (ATD = amino triphenylamine dendron, QD = CdSe/ZnSe quantum dot, E2Zn2SOD = Cu-free derivative of bovine liver copper-zinc superoxide dismutase), for imaging and sensing the changes of intracellular Cu(2+) level with clear red-to-yellow color change based on specific biomolecular recognition of E2Zn2SOD for Cu(2+) ion. The inorganic-organic nanohybrided fluorescent probe features two independent emission peaks located at 515 nm for ATD and 650 nm for QDs, respectively, under two-photon excitation at 800 nm. Upon addition of Cu(2+) ions, the red fluorescence of QDs drastically quenches, while the green emission from ATD stays constant and serves as a reference signal, thus resulting in the ratiometric detection of Cu(2+) with high accuracy by two-photon microscopy (TPM). The present probe shows high sensivity, broad linear range (10(-7)-10(-3) M), low detection limit down to ∼10 nM, and excellent selectivity over other metal ions, amino acids, and other biological species. Meanwhile, a QD-based inorganic-organic probe demonstrates long-term photostability, good cell-permeability, and low cytotoxicity. As a result, the present probe can visualize Cu(2+) changes in live cells by TPM. To the best of our knowledge, this is the first report for the development of a QD-based two-photon ratiometric fluorescence probe suitable for detection of Cu(2+) in live cells.

Architecture of optical sensor for recognition of multiple toxic metal ions from water

Here, we designed novel optical sensor based on the wormhole hexagonal mesoporous core/multi-shell silica nanoparticles that enabled the selective recognition and removal of these extremely toxic metals from drinking water. The surface-coating process of a mesoporous core/double-shell silica platforms by several consequence decorations using a cationic surfactant with double alkyl tails (CS-DAT) and then a synthesized dicarboxylate 1,5-diphenyl-3-thiocarbazone (III) signaling probe enabled us to create a unique hierarchical multi-shell sensor. In this design, the high loading capacity and wrapping of the CS-DAT and III organic moieties could be achieved, leading to the formation of silica core with multi-shells that formed from double-silica, CS-DAT, and III dressing layers. In this sensing system, notable changes in color and reflectance intensity of the multi-shelled sensor for Cu(2+), Co(2+), Cd(2+), and Hg(2+) ions, were observed at pH 2, 8, 9.5 and 11.5, respectively. The multi-shelled sensor is added to enable accessibility for continuous monitoring of several different toxic metal ions and efficient multi-ion sensing and removal capabilities with respect to reversibility, selectivity, and signal stability.

Plasmon resonance scattering spectroscopy at the single-nanoparticle level: real-time monitoring of a click reaction

A method based on plasmon resonance Rayleigh scattering (PRRS) spectroscopy and dark-field microscopy (DFM) was established for the real-time monitoring of a click reaction at the single-nanoparticle level. Click reactions on the surface of single gold nanoparticles (GNPs) result in interparticle coupling, which leads to a red-shift of the λmax (Δλmax =43 nm) in the PRRS spectra and a color change of the single gold nanoparticles in DFM (from green to orange).

Dual-responsive gold nanoparticles for colorimetric recognition and testing of carbohydrates with a dispersion-dominated chromogenic process

A dispersion-dominated colorimetric approach for the recognition of carbohydrates based on biomolecule-responsive AuNPs is presented. Taking advantage of the unique dual-responsiveness of smart copolymers, the aggregation and dispersion of AuNPs can be modulated by both temperature and different kinds of carbohydrates, giving rise to a novel chromogenic mechanism for the recognition and testing of carbohydrates in aqueous media.

A REVERSIBLE OPTICAL SENSOR BASED ON CHITOSAN FILM FOR THE SELECTIVE DETECTION OF COPPER IONS

Heavy metals greatly influence animal physiology, even at small doses. Among these metals, the copper ion is of great concern due to its effects on humans and wide applications in industry. Compared to atomic absorption spectroscopy and inductively coupled plasma-mass spectrometry, which destroy the samples that are analyzed, optical techniques do not decompose the analyte and have become a popular field of recent research. In this paper, we combined a novel optical detector that did not require sample-labeling, called surface plasmon resonance (SPR), with chitosan to detect copper ions by modifying the functional groups of chitosan through pH modification. Compared to other optical detectors, the SPR system was relatively fast and involved fewer experimental confounding factors. The three-dimensional structure of chitosan was used to obtain lower detection limits. Moreover, modification of the chitosan functional groups resulted in efficient regeneration by controlling the pH. A detection limit of 0.1 μM was obtained (linear range: 0.5–10 μM, R2 = 0.976), and the specificity was certified by comparing the copper ion with six other ions. Additionally, we successfully regenerated the SPR chips by modifying the functional groups. In conclusion, the chitosan–SPR system detected copper ions with improved detection limits using a quick and simple regeneration method.

Setting the environmental conditions for controlling gold nanoparticle assemblies

Fundamental insights into the factors that control the properties and structure of gold nanoparticle (AuNP) based assemblies enable the design and construction of new materials. The dimensions (shape and size) and the optical properties of AuNP assemblies are affected by the electronic properties of the organic cross-linker and the nature of the AuNPs.

Luminescence of polyethylene glycol coated CdSeTe/ZnS and InP/ZnS nanoparticles in the presence of copper cations

The use of click chemistry for quantum dot (QD) functionalization could be very promising for the development of bioconjugates dedicated to in vivo applications. Alkyne-azide ligation usually requires copper(I) catalysis. The luminescence response of CdSeTe/ZnS nanoparticles coated with polyethylene glycol (PEG) is studied in the presence of copper cations, and compared to that of InP/ZnS QDs coated with mercaptoundecanoic acid (MUA). The quenching mechanisms appear different. Luminescence quenching occurs without any wavelength shift in the absorption and emission spectra for the CdSeTe/ZnS/PEG nanocrystals. In this case, the presence of copper in the ZnS shell is evidenced by energy-filtered transmission electron microscopy (EF-TEM). By contrast, in the case of InP/ZnS/MUA nanocrystals, a redshift of the excitation and emission spectra, accompanied by an increase in absorbance and a decrease in photoluminescence, is observed. For CdSeTe/ZnS/PEG nanocrystals, PL quenching is enhanced for QDs with 1) smaller inorganic-core diameter, 2) thinner PEG shell, and 3) hydroxyl terminal groups. Whereas copper-induced PL quenching can be interesting for the design of sensitive cation sensors, copper-free click reactions should be used for the efficient functionalization of nanocrystals dedicated to bioapplications, in order to achieve highly luminescent QD bioconjugates.