Dual Signal Amplification Electrochemical Biosensor for Lead Cation

Herein, a sensitive electrochemical Pb²⁺ sensor was developed which based on DNA‐functionalized Au nanoparticles(AuNPs) and nanocomposite modified electrode. The DNA‐functionalized AuNPs includes two types of DNA, namely a Pb²⁺‐mediated DNAzyme comprising a biotin labeled‐enzyme DNA and a substrate strand DNA with a typical stem‐loop structure, and a ferrocene‐labeled linear signal DNA. Without Pb²⁺, the hairpin loop impeded biotin binding to avidin on the electrode. However,when the goal Pb²⁺ exists, the substratum strand was divided into two fragments that lead to the enzyme strand was substratumed on the electrode and biotin was admited by avidin, bringing about DNA‐functionalized AuNP(AuNPs) deposition on the electrode surface.The differential pulse voltammetry (DPV) was used to measure electrochemical response signals connect to signal DNA.For the amplification characters of the DNA‐functionalized AuNPs and nanocomposite, the electrochemical detection signal of Pb²⁺ was greatly improved and revealed high specificity. Under optimum conditions, the resultant biosensor bringed out a high sensitivity and selectivity for the determination of Pb²⁺. The proposed method was able to detect as low as picomolar Pb²⁺ concentrations.     

Optofluidics-based DNA structure-competitive aptasensor for rapid on-site detection of lead(II) in an aquatic environment

Lead ions (Pb²⁺), ubiquitous and one of the most toxic metallic pollutants, have attracted increasing attentions because of their various neurotoxic effects. Pb²⁺ has been proven to induce a conformational change in G-quadruplex (G4) aptamers to form a stabilizing G4/Pb²⁺ complex. Based on this principle, an innovative optofluidics-based DNA structure-competitive aptasensor was developed for Pb²⁺ detection in an actual aquatic environment. The proposed sensing system has good characteristics, such as high sensitivity and selectivity, reusability, easy operation, rapidity, robustness, portability, use of a small sample volume, and cost effectiveness. A fluorescence-labeled G4 aptamer was utilized as a molecular probe. A DNA probe, a complementary strand of G4 aptamer, was immobilized onto the sensor surface. When the mixture of Pb²⁺ solution and G4 aptamer was introduced into the optofluidic cell, Pb²⁺ and the DNA probe bound competitively with the G4 aptamer. A high Pb²⁺ concentration reduced the binding of the aptamer and the DNA probe; thus, a low-fluorescence signal was detected. A sensitive sensing response to Pb²⁺ in the range of 1.0–300.0 nM with a low detection limit of 0.22 nM was exhibited under optimal conditions. The potential interference of the environmental sample matrix was assessed with spiked samples, and the recovery of Pb²⁺ ranged from 80 to 105% with a relative standard deviation value of <8.5%. These observations clearly illustrate that with the use of different DNA or aptamer probes, the sensing strategy presented can be easily extended to the rapid on-site monitoring of other trace analytes.     

Amperometric Glucose Biosensor Based on Electrochemically Deposited Gold Nanoparticles Covered by Polypyrrole

Graphite rod (GR) modified with electrochemicaly deposited gold nanoparticles (AuNPs) and adsorbed glucose oxidase (GOx) was used in amperometric glucose biosensor design. Enzymatic formation of polypyrrole (Ppy) on the surface of GOx/AuNPs/GR electrode was applied in order to improve analytical characteristics and stability of developed biosensor. The linear glucose detection range for Ppy/GOx/AuNPs/GR electrode was dependent on the duration of Ppy‐layer formation and the linear interval was extended up to 19.9 mmol L⁻¹ after 21 h lasting synthesis of Ppy. The sensitivity of the developed biosensor was determined as 21.7 μA mM⁻¹ cm⁻², the limit of detection – 0.20 mmol L⁻¹. Ppy/GOx/AuNPs/GR electrodes demonstrated advanced good stability (the t _1/2 was 9.8 days), quick detection of glucose (within 5 s) in the wide linear interval. Additionally, formed Ppy layer decreased the influence of electroactive species on the analytical signal. Developed biosensor is suitable for the determination of glucose in human serum samples.     

Sensitive Stripping Determination of Cadmium(II) and Lead(II) on Disposable Graphene Modified Screen‐Printed Electrode

In the present work, a sensitive, facile and disposable sensing platform for trace analysis of heavy metal ions was developed at the Bi modified graphene‐poly(sodium 4‐styrenesulfonate) composite film screen printed electrode (GR/PSS/Bi/SPE). The GR/PSS/Bi/SPE improved sensitivity and linearity due to the functionalization of graphene with negatively charged PSS providing more absorbing sites. The detection limit of the GR/PSS/Bi/SPE is found to be 0.042 µg L^?1 for Cd²⁺ and 0.089 µg L^?1 for Pb²⁺ with linear responses of Cd²⁺ and Pb²⁺ in the range of 0.5–120 µg L^?1. Finally, the practical application was confirmed in real water with satisfactory results.     

A sensitive fluorescence anisotropy method for detection of lead (II) ion by a G-quadruplex-inducible DNA aptamer

Sensitive and selective detection of Pb²⁺ is of great importance to both human health and environmental protection. Here we propose a novel fluorescence anisotropy (FA) approach for sensing Pb²⁺ in homogeneous solution by a G-rich thrombin binding aptamer (TBA). The TBA labeled with 6-carboxytetramethylrhodamine (TMR) at the seventh thymine nucleotide was used as a fluorescent probe for signaling Pb²⁺. It was found that the aptamer probe had a high FA in the absence of Pb²⁺. This is because the rotation of TMR is restricted by intramolecular interaction with the adjacent guanine bases, which results in photoinduced electron transfer (PET). When the aptamer probe binds to Pb²⁺ to form G-quadruplex, the intramolecular interaction should be eliminated, resulting in faster rotation of the fluorophore TMR in solution. Therefore, FA of aptamer probe is expected to decrease significantly upon binding to Pb²⁺. Indeed, we observed a decrease in FA of aptamer probe upon Pb²⁺ binding. Circular dichroism, fluorescence spectra, and fluorescence lifetime measurement were used to verify the reliability and reasonability of the sensing mechanism. By monitoring the FA change of the aptamer probe, we were able to real-time detect binding between the TBA probe and Pb²⁺. Moreover, the aptamer probe was exploited as a recognition element for quantification of Pb²⁺ in homogeneous solution. The change in FA showed a linear response to Pb²⁺ from 10 nM to 2.0 μM, with 1.0 nM limit of detection. In addition, this sensing system exhibited good selectivity for Pb²⁺ over other metal ions. The method is simple, quick and inherits the advantages of aptamer and FA.     

A colorimetric and surface-enhanced Raman scattering dual-signal sensor for Hg based on Bismuthiol II-capped gold nanoparticles

The addition of Bismuthiol II to the gold nanoparticles (AuNPs) solution led to the aggregation of AuNPs with a color change from red to blue. As a result, hot spots were formed and strong surface-enhanced Raman scattering (SERS) signal of Bismuthiol II was observed. However, the Bismuthiol II-induced aggregation of AuNPs could be reversed by Hg²⁺ in the system, accompanied by a remarkable color change from blue to red. As evidenced by UV–vis and SERS spectroscopy, the variation in absorption band and SERS intensity was strongly dependent on the concentration of Hg²⁺, suggesting a colorimetric and SERS dual-signal sensor for Hg²⁺. The sensor had a high sensitivity, low detection limits of 2 nM and 30 nM could be achieved by UV–vis spectroscopy and by SERS spectroscopy, respectively. Other environmentally relevant metal ions did not interfere with the detection of Hg²⁺. The method was successfully applied to detect Hg²⁺ in water samples. It was simple, rapid and cost-effective without any modifying or labeling procedure.     

Copper sulfide nanoparticle-decorated graphene as a catalytic amplification platform for electrochemical detection of alkaline phosphatase activity

Copper sulfide nanoparticle-decorated graphene sheet (CuS/GR) was successfully synthesized and used as a signal amplification platform for electrochemical detection of alkaline phosphatase activity. First, CuS/GR was prepared through a microwave-assisted hydrothermal approach. The CuS/GR nanocomposites exhibited excellent electrocatalytic activity toward the oxidation of ALP hydrolyzed products such as 1-naphthol, which produced a current response. Thus, a catalytic amplification platform based on CuS/GR nanocomposite for electrochemical detection of ALP activity was designed using 1-naphthyl phosphate as a model substrate. The current response increased linearly with ALP concentration from 0.1 to 100 U L⁻¹ with a detection limit of 0.02 U L⁻¹. The assay was applied to estimate ALP activity in human serum samples with satisfactory results. This strategy may find widespread and promising applications in other sensing systems that involves ALP.     

Construction of a Graphene/Au‐Nanoparticles/Cucurbit[7]uril‐Based Sensor for Pb2+ Sensing

The development of highly sensitive and selective methods for the detection of lead ion (Pb²⁺) is of great scientific importance. In this work, we develop a new surface‐enhanced Raman scattering (SERS)‐based sensor for the selective trace measurement of Pb²⁺. The SERS‐based sensor is assembled from gold nanoparticles (AuNPs) and graphene using cucurbit[7]uril (CB[7]) as a precise molecular glue and a local SERS reporter. Upon the addition of Pb²⁺, CB[7] forms stronger complexes with Pb²⁺ and desorbs from AuNPs, resulting in a sensitive “turn‐off” of SERS signals. This SERS‐based assay shows a limit of detection (LOD) of 0.3 nm and a linear detection range from 1 nm to 0.3 μm for Pb²⁺. The feasibility of the assay is further demonstrated by probing Pb²⁺ in real water samples. This SERS‐based analytical method is highly sensitive and selective, and therefore holds promising applications in environmental analysis.     

Target-responsive DNAzyme hydrogel for portable colorimetric detection of lanthanide(III) ions

Lanthanide elements (Ln) play an important role in industry and agriculture. As a result of the increasing consumption of lanthanides, environmental emission of Ln has become detrimental to the health of flora and fauna. Current methods for trace lanthanides detection mainly rely on sophisticated instruments. In this article, a Ln³⁺ dependent DNAzyme was incorporated into a hydrogel to generate Ln³⁺ sensitive DNAzyme hydrogel for portable colorimetric detection. The enzyme strand and its substrate strand act as crosslinker and functional unit of the hydrogel with polyacrylamide chains as the scaffold and gold nanoparticles (AuNPs) as the indicator of hydrogel stability. Any ions in the Ln³⁺ series can trigger the cleavage of substrate strand by activating the enzyme strand, thereby decreasing the crosslink ratio and leading to collapse of the hydrogel. The release of the encapsulated AuNPs turns the supernatant wine red. Using this colorimetric method, Ln³⁺ can be detected with high sensitivity, with a limit of detection (LOD) of 20 nM for Ce³⁺. The hydrogel responds specifically to any Ln³⁺ ion and works well with the spiked lake sample without the need of instruments and skilled operators. Our results suggest that the lanthanide responsive hydrogel can be used for portable and sensitive detection of Ln³⁺ contamination in the field.     

Gold nanoparticles decorated carbon fiber mat as a novel sensing platform for sensitive detection of Hg(II)

The three-dimensional fibril-like carbon fiber mat electrode (CFME) decorated with Au nanoparticles (AuNPs) was employed to construct Hg(II) sensing platform for the first time. The highly porous feature of CFME combining the high affinity of AuNPs for mercury endowed the sensing platform with high sensitivity and good reproducibility. Under optimal conditions, the prepared AuNPs/CFME was capable of sensing Hg(II) with a detection limit of 0.1 μg L^− 1 (S/N = 3) using differential pulse anodic stripping voltammetry (DPASV). Finally, the AuNPs/CFME was successfully demonstrated for the determination of Hg(II) in real water samples with satisfactory results.     

A label-free and signal-on supersandwich fluorescent platform for Hg sensing

A label-free supersandwich fluorescent assay was demonstrated for the first time by taking Hg²⁺ as a detection candidate. The principle of the proposed supersandwich fluorescent platform is based on the formation of supersandwich structure by T-Hg²⁺-T coordination and the fluorescence enhancement of the intercalated Genefinder (GF) in double strand DNA (dsDNA). Such supersandwich fluorescent DNA sensor exhibits a linear range of 10–300 nM for the detection of Hg²⁺, with a detection limit of 2.5 nM on the basis of the 3σ/slope (σ represents the standard deviation of the blank samples), which is well below the permit of the U.S. Environmental Protection Agency (<10 nM). The detection can be fulfilled in less than 10 min. The proposed mix-and-detect fluorescent platform exhibits excellent sensitivity, selectivity, and convenient manipulation. The assay was successfully used to detect Hg²⁺ in the lake water samples, which suggested its potential in practical samples.     

Highly selective piezoelectric sensor for lead(II) based on the lead-catalyzed release of gold nanoparticles from a self-assembled nanosurface

A novel quartz crystal microbalance (QCM) sensor has been developed for highly selective and sensitive detection of Pb²⁺ by exploiting the catalytic effect of Pb²⁺ ions on the leaching of gold nanoparticles from the surface of a QCM sensor. The use of self-assembled gold nanoparticles (AuNPs) strongly enlarges the size of the interface and thus amplifies the analytical response resulting from the loss of mass. This results in a very low detection limit for Pb²⁺ (30 nM). The high selectivity is demonstrated by studying the effect of potentially interfering ions both in the absence and presence of Pb²⁺ ions. This simple and well reproducible sensor was applied to the determination of lead in the spiked drinking water. This work provides a novel strategy for fabricating QCM sensors towards Pb²⁺ in real samples. Figure

?     

A Sandwich‐type Electrochemiluminescence Aptasensor for Thrombin Based on Functional Co‐polymer Electrode Using Ru(bpy)32+ Doped Nanocomposites as Signal‐amplifying Tags

Herein, a signal‐on sandwich‐type electrochemiluminescence (ECL) aptasensor for the detection of thrombin (TB) was proposed. The graphene (GR) doped thionine (TH) was electropolymerized synchronously on the bare glassy carbon electrode (GCE) to form co‐polymer (PTG) electrode. The gold nanoparticles (AuNPs) were decorated on the surface of the PTG by in‐situ electrodeposition, and the functional co‐polymer (PTG‐AuNPs) electrode was utilized as sensing interface. Then, TB binding aptamer I (TBA I) as capture probes were modified on the PTG‐AuNPs electrode to capture TB, and Ru(bpy)₃²⁺/silver nanoparticles doped silica core‐shell nanocomposites‐labeled TB binding aptamer II (RuAg/SiO₂NPs@TBA II) were used as signal probes to further bind TB, resulting in a sandwich structure. With the assistant of silica shell and AgNPs, the enrichment and luminous efficiency of Ru(bpy)₃²⁺ were significantly improved. Under the synergy of PTG‐AuNPs and RuAg/SiO₂NPs, the ECL signal was dramatically increased. The proposed ECL aptasensor displayed a wide linear range from 2 fM to 2 pM with the detection limit of 1 fM, which is comparable or better than that in reported ECL aptasensors for TB using Ru(bpy)₃²⁺ and its derivatives as the luminescent substance. The excellent sensitivity makes the proposed aptasensor a promising potential in pharmaceutical and clinical analysis.     

Aptamer-Based Fluorescence Nanoprobe for Sensitive and Selective Detection of Potassium

A new aptamer-based fluorescence nanoprobe for potassium ion (K⁺) has been developed. The nanoprobe employs gold nanoparticles (AuNPs) as the sensing platform and Rhodamine B as the fluorescence indicator. Aptamer acts as the switch of fluorescence signal of Rhodamine B. In the presence of K⁺, aptamer departs from AuNPs as a result of the formation of G-quartets with K⁺, leading to the decrease of fluorescence signals. Under the optimum conditions, the limit of detection (LOD) for K⁺ is as low as 3.8 nM. The proposed method was successfully applied in the determination of K⁺ in human saliva sample.     

Visual and surface plasmon resonance sensor for zirconium based on zirconium-induced aggregation of adenosine triphosphate-stabilized gold nanoparticles

Owing to its high affinity with phosphate, Zr(IV) can induce the aggregation of adenosine 5′-triphosphate (ATP)-stabilized AuNPs, leading to the change of surface plasmon resonance (SPR) absorption spectra and color of ATP-stabilized AuNP solutions. Based on these phenomena, visual and SPR sensors for Zr(IV) have been developed for the first time. The A_660 nm/A_518 nm values of ATP-stabilized AuNPs in SPR absorption spectra increase linearly with the concentrations of Zr(IV) from 0.5 μM to 100 μM (r = 0.9971) with a detection limit of 95 nM. A visual Zr(IV) detection is achieved with a detection limit of 30 μM. The sensor shows excellent selectivity against other metal ions, such as Cu²⁺, Fe³⁺, Cd²⁺, and Pb²⁺. The recoveries for the detection of 5 μM, 10 μM, 25 μM and 75 μM Zr(IV) in lake water samples are 96.0%, 97.0%, 95.6% and 102.4%, respectively. The recoveries of the proposed SPR method are comparable with those of ICP-OES method.     

Aminoquinoline based highly sensitive fluorescent sensor for lead(II) and aluminum(III) and its application in live cell imaging

We have synthesized a new probe 5-((anthracen-9-ylmethylene) amino)quinolin-10-ol (ANQ) based on anthracene platform. The probe was tested for its sensing behavior toward heavy metal ions Hg²⁺, Pb²⁺, light metal Al³⁺ ion, alkali, alkaline earth, and transition metal ions by UV–visible and fluorescent techniques in ACN/H₂O mixture buffered with HEPES (pH 7.4). It shows high selectivity toward sensing Pb²⁺/Al³⁺ metal ions. Importantly, 10-fold and 5- fold fluorescence enhancement at 429 nm was observed for probe upon complexation with Pb²⁺ and Al³⁺ ions, respectively. This fluorescence enhancement is attributable to the prevention of photoinduced electron transfer. The photonic studies indicate that the probe can be adopted as a sensitive fluorescent chemosensor for Pb²⁺ and Al³⁺ ions.     

A novel biomimetic logic gate for sensitive and selective detection of Pb(II) base on porous alumina nanochannels

A novel biomimetic logic gate sensor for Pb^2 + is established using porous alumina membrane nanochannels modified with morpholino and DNA. It is based on electrochemical detection, and the current response from the diffusion flux of Fe(CN)₆^3 − is influenced by the steric blockage and charge repulsion in nanochannels. A limit of detection (0.1 nM) and good linear range (0.1 nM–5 μM) for Pb^2 + analysis are achieved in the tenth cycle. The sensing strategy shows prospective application in drug release, artificial ion channels, DNA logic gates for controlling biomolecule, and ion translocation.     

Non-conductive nanomaterial enhanced electrochemical response in stripping voltammetry: The use of nanostructured magnesium silicate hollow spheres for heavy metal ions detection

Nanostructured magnesium silicate hollow spheres, one kind of non-conductive nanomaterials, were used in heavy metal ions (HMIs) detection with enhanced performance for the first time. The detailed study of the enhancing electrochemical response in stripping voltammetry for simultaneous detection of ultratrace Cd²⁺, Pb²⁺, Cu²⁺ and Hg²⁺ was described. Electrochemical properties of modified electrodes were characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The operational parameters which have influence on the deposition and stripping of metal ions, such as supporting electrolytes, pH value, and deposition time were carefully studied. The anodic stripping voltammetric performance toward HMIs was evaluated using square wave anodic stripping voltammetry (SWASV) analysis. The detection limits achieved (0.186 nM, 0.247 nM, 0.169 nM and 0.375 nM for Cd²⁺, Pb²⁺, Cu²⁺ and Hg²⁺) are much lower than the guideline values in drinking water given by the World Health Organization (WHO). In addition, the interference and stability of the modified electrode were also investigated under the optimized conditions. An interesting phenomenon of mutual interference between different metal ions was observed. Most importantly, the sensitivity of Pb²⁺ increased in the presence of certain concentrations of other metal ions, such as Cd²⁺, Cu²⁺ and Hg²⁺ both individually and simultaneously. The proposed electrochemical sensing method is thus expected to open new opportunities to broaden the use of SWASV in analysis for detecting HMIs in the environment.     

A label-free colorimetric detection of lead ions by controlling the ligand shells of gold nanoparticles

We have developed a simple, colorimetric and label-free gold nanoparticle (Au NP)-based probe for the detection of Pb²⁺ ions in aqueous solution, operating on the principle that Pb²⁺ ions change the ligand shell of thiosulfate (S₂O₃²⁻)-passivated Au NPs. Au NPs reacted with S₂O₃²⁻ ions in solution to form Au⁺·S₂O₃²⁻ ligand shells on the Au NP surfaces, thereby inhibiting the access of 4-mercaptobutanol (4-MB). Surface-assisted laser desorption/ionization time-of-flight ionization mass spectrometry (SALDI-TOF MS) and inductively coupled plasma mass spectrometry (ICP-MS) measurements revealed that PbAu alloys formed on the surfaces of the Au NPs in the presence of Pb²⁺ ions; these alloys weakened the stability of the Au⁺·S₂O₃²⁻ ligand shells, enhancing the access of 4-MB to the Au NP surfaces and, therefore, inducing their aggregation. As a result, the surface plasmon resonance (SPR) absorption of the Au NPs red-shifted and broadened, allowing quantitation of the Pb²⁺ ions in the aqueous solution. This 4-MB/S₂O₃²⁻-Au NP probe is highly sensitive (linear detection range: 0.5-10 nM) and selective (by at least 100-fold over other metal ions) toward Pb²⁺ ions. This cost-effective sensing system allows the rapid and simple determination of the concentrations of Pb²⁺ ions in real samples (in this case, river water, Montana soil and urine samples).     

Target-induced formation of gold amalgamation on DNA-based sensing platform for electrochemical monitoring of mercury ion coupling with cycling signal amplification strategy

Heavy metal ion pollution poses severe risks in human health and environmental pollutant, because of the likelihood of bioaccumulation and toxicity. Driven by the requirement to monitor trace-level mercury ion (Hg²⁺), herein we construct a new DNA-based sensor for sensitive electrochemical monitoring of Hg²⁺ by coupling target-induced formation of gold amalgamation on DNA-based sensing platform with gold amalgamation-catalyzed cycling signal amplification strategy. The sensor was simply prepared by covalent conjugation of aminated poly-T₍₂₅₎ oligonucleotide onto the glassy carbon electrode by typical carbodiimide coupling. Upon introduction of target analyte, Hg²⁺ ion was intercalated into the DNA polyion complex membrane based on T–Hg²⁺–T coordination chemistry. The chelated Hg²⁺ ion could induce the formation of gold amalgamation, which could catalyze the p-nitrophenol with the aid of NaBH₄ and Ru(NH₃)₆³⁺ for cycling signal amplification. Experimental results indicated that the electronic signal of our system increased with the increasing Hg²⁺ level in the sample, and has a detection limit of 0.02 nM with a dynamic range of up to 1000 nM Hg²⁺. The strategy afforded exquisite selectivity for Hg²⁺ against other environmentally related metal ions. In addition, the methodology was evaluated for the analysis of Hg²⁺ in spiked tap-water samples, and the recovery was 87.9–113.8%.