Ultrasensitive flow injection chemiluminescence detection of DNA hybridization using signal DNA probe modified with Au and CuS nanoparticles

A novel and sensitive flow injection chemiluminescence assay for sequence-specific DNA detection based on signal amplification with nanoparticles (NPs) is reported in the present work. The "sandwich-type" DNA biosensor was fabricated with the thiol-functionalized capture DNA first immobilized on an Au electrode and hybridized with one end of target DNA, the other end of which was recognized with a signal DNA probe labeled with CuS NPs and Au NPs on the 3'- and 5'-terminus, respectively. The hybridization events were monitored by the CL intensity of luminol-H2O2-Cu(2+) after the cupric ions were dissolved from the hybrids. We demonstrated that the incorporation of Au NPs in this sensor design significantly enhanced the sensitivity and the selectivity because a single Au NP can be loaded with hundreds of signal DNA probe strands, which were modified with CuS NPs. The ratios of Au NPs, signal DNA probes, and CuS NPs modified on the gold electrode were approximately 1/101/103. A preconcentration process of cupric ions performed by anodic stripping voltammetry technology further increased the sensor performance. As a result of these two combined effects, this DNA sensor could detect as low as femtomolar target DNA and exhibited excellent selectivity against two-base mismatched DNA. Under the optimum conditions, the CL intensity was increased with the increase of the concentration of target DNA in the range of 2.0 x 10(-14)-2.0 x 10(-12) M. A detection limit of 4.8 x 10(-15) M target DNA was achieved.     

Hg(II) ion detection using thermally reduced graphene oxide decorated with functionalized gold nanoparticles

Fast and accurate detection of aqueous contaminants is of significant importance as these contaminants raise serious risks for human health and the environment. Mercury and its compounds are highly toxic and can cause various illnesses; however, current mercury detectors suffer from several disadvantages, such as slow response, high cost, and lack of portability. Here, we report field-effect transistor (FET) sensors based on thermally reduced graphene oxide (rGO) with thioglycolic acid (TGA) functionalized gold nanoparticles (Au NPs) (or rGO/TGA-AuNP hybrid structures) for detecting mercury(II) ions in aqueous solutions. The lowest mercury(II) ion concentration detected by the sensor is 2.5 × 10(-8) M. The drain current shows rapid response within less than 10 s after the solution containing Hg(2+) ions was added to the active area of the rGO/TGA-AuNP hybrid sensors. Our work suggests that rGO/TGA-AuNP hybrid structures are promising for low-cost, portable, real-time, heavy metal ion detectors.     

Colorimetric assay of lead ions in biological samples using a nanogold-based membrane

We have developed a simple paper-based colorimetric membrane for sensing lead ions (Pb(2+)) in aqueous solutions. The nitrocellulose membrane (NCM) was used to trap bovine serum albumin (BSA) modified 13.3-nm Au nanoparticles (BSA-Au NPs), leading to the preparation of a nanocomposite film of a BSA-Au NP-decorated membrane (BSA-Au NPs/NCM). The BSA-Au NPs/NCM operates on the principle that Pb(2+) ions accelerate the rate of leaching of Au NPs induced by thiosulfate (S(2)O(3)(2-)) and 2-mercaptoethanol (2-ME). The BSA-Au NPs/NCM allowed for the detection of Pb(2+) by the naked eye in nanomolar aqueous solutions in the presence of leaching agents such as S(2)O(3)(2-) and 2-ME. We employed the assistance of microwave irradiation to shorten the reaction time (<10 min) for leaching the Au NPs. Under optimal solution conditions (5 mM glycine-NaOH (pH 10), S(2)O(3)(2-) (100 mM), and 2-ME (250 mM), microwaves (450 W)), the BSA-Au NPs/NCM allowed the detection of Pb(2+) at concentrations as low as 50 pM with high selectivity (at least 100-fold over other metal ions). This cost-effective sensing system allowed for the rapid and simple determination of the concentrations of Pb(2+) ions in real samples (in this case, sea water, urine, and blood samples).     

Self-powered sensor for trace Hg2+ detection

A self-powered electrochemical sensor has been facilely designed for sensitive detection of Hg(2+) based on the inhibition of biocatalysis process of enzymatic biofuel cell (BFC) for the first time. The as-prepared one-compartment BFC, which was consisted of alcohol dehydrogenase supported on single-walled carbon nanohorns-based mediator system as the anode and bilirubin oxidase as the cathodic biocatalyst, generated an open circuit potential (V(oc)) of 636 mV and a maximum power density of 137 μW cm(-2). It was interestingly found that the presence of Hg(2+) would affect the performance of the constructed BFC (e.g., V(oc)). Taking advantage of the inhibitive effect of Hg(2+), a novel self-powered Hg(2+) sensor has been developed, which showed a linear range of 1-500 nM (R(2) = 0.999) with a detection limit of 1 nM at room temperature. In addition, this BFC-type sensor exhibited good selectivity for Hg(2+) against other common environmental metal ions, and the feasibility of the method for Hg(2+) detection in actual water samples (i.e., tap, ground, and lake water) was demonstrated with satisfactory results.     

Luminescent, freestanding composite films of Au15 for specific metal ion sensing

A highly luminescent freestanding film composed of the quantum cluster, Au(15), was prepared. We studied the utility of the material for specific metal ion detection. The sensitivity of the red emission of the cluster in the composite to Cu(2+) has been used to make a freestanding metal ion sensor, similar to pH paper. The luminescence of the film was stable when exposed to several other metal ions such as Hg(2+), As(3+), and As(5+). The composite film exhibited visual sensitivity to Cu(2+) up to 1 ppm, which is below the permissible limit (1.3 ppm) in drinking water set by the U.S. environmental protection agency (EPA). The specificity of the film for Cu(2+) sensing may be due to the reduction of Cu(2+) to Cu(1+)/Cu(0) by the glutathione ligand or the Au(15) core. Extended stability of the luminescence of the film makes it useful for practical applications.     

Colorimetric detection of trace copper ions based on catalytic leaching of silver-coated gold nanoparticles

A colorimetric, label-free, and nonaggregation-based silver coated gold nanoparticles (Ag/Au NPs) probe has been developed for detection of trace Cu(2+) in aqueous solution, based on the fact that Cu(2+) can accelerate the leaching rate of Ag/Au NPs by thiosulfate (S(2)O(3)(2-)). The leaching of Ag/Au NPs would lead to dramatic decrease in the surface plasmon resonance (SPR) absorption as the size of Ag/Au NPs decreased. This colorimetric strategy based on size-dependence of nanoparticles during their leaching process provided a highly sensitive (1.0 nM) and selective detection toward Cu(2+), with a wide linear detection range (5-800 nM) over nearly 3 orders of magnitude. The cost-effective probe allows rapid and sensitive detection of trace Cu(2+) ions in water samples, indicating its potential applicability for the determination of copper in real samples.     

Quinolino-triazole linked gold nanoparticles as sensitive 'turn-on' fluorescent Cd(2+) probes

Quinoline derivatives were brought into the surface of gold nanoparticles (Au NPs) through click chemistry. The fluorescence was quenched by Au NPs because of electron transfer between Au NPs and quinoline. However, upon addition of Cd(2+) to the quinoline-triazole Au NP solution, it exhibited an effective switch-on fluorescence response, owing to the coordination between quinoline and Cd(2+) which can efficiently block the electron transfer. What's more, the fluorescent sensor can effectively detect Cd(2+) in aqueous solution with a detection limit of 1.0 × 10(-5) M.     

Amplified surface plasmon resonance and electrochemical detection of Pb2+ ions using the Pb2+-dependent DNAzyme and hemin/G-quadruplex as a label

The hemin/G-quadruplex nanostructure and the Pb(2+)-dependent DNAzyme are implemented to develop sensitive surface plasmon resonance (SPR) and electrochemical sensing platforms for Pb(2+) ions. A complex consisting of the Pb(2+)-dependent DNAzyme sequence and a ribonuclease-containing nucleic acid sequence (corresponding to the substrate of the DNAzyme) linked to a G-rich domain, which is "caged" in the complex structure, is assembled on Au-coated glass surfaces or Au electrodes. In the presence of Pb(2+) ions, the Pb(2+)-dependent DNAzyme cleaves the substrate, leading to the separation of the complex and to the self-assembly of the hemin/G-quadruplex on the Au support. In one sensing platform, the Pb(2+) ions are analyzed by following the dielectric changes at the surface as a result of the formation of the hemin/G-quadruplex label using SPR. This sensing platform is further amplified by the immobilization of the sensing complex on Au NPs (13 nm) and using the electronic coupling between the NPs and the surface plasmon wave as an amplification mechanism. This method enables the sensing of Pb(2+) ions with a detection limit that corresponds to 5 fM. The second sensing platform implements the resulting hemin/G-quadruplex as an electrocatalytic label that catalyzes the electrochemical reduction of H(2)O(2). This method enables the detection of Pb(2+) with a detection limit of 1 pM. Both sensing platforms reveal selectivity toward the detection of Pb(2+) ions.     

A new Schiff's base ligand immobilized agarose membrane optical sensor for selective monitoring of mercury ion

A highly selective optical sensor was developed for the Hg(2+) determination by chemical immobilization of 2-[(2-sulfanylphenyl)ethanimidoyl]phenol (L), on an agarose membrane. Spectrophotometric studies of complex formation between the Schiff's base ligand L and Hg(2+), Sr(2+), Mn(2+), Cu(2+), Al(3+), Cd(2+), Zn(2+), Co(2+) and Ag(+) metal ions in methanol solution indicated a substantially larger stability constant for the mercury ion complex. Consequently, the Schiff's base L was used as an appropriate ionophore for the preparation of a selective Hg(2+) optical sensor, by its immobilization on a transparent agarose film. A distinct color change, from yellow to green-blue, was observed by contacting the sensing membrane with Hg(2+) ions at pH 4.5. The effects of pH, ionophore concentration, ionic strength and reaction time on the immobilization of L were studied. A linear relationship was observed between the membrane absorbance at 650 nm and Hg(2+) concentrations in a range from 1×10(-2) to 1×10(-5) mol L(-1) with a detection limit (3σ) of 1×10(-6) mol L(-1). No significant interference from 100 times concentrations of a number of potentially interfering ions was detected for the mercury ion determination. The optical sensor was successfully applied to the determination of mercury in amalgam alloy and spiked water samples.     

Ultrasensitive sensing of Hg(2+) and CH(3)Hg(+) based on the fluorescence quenching of lysozyme type VI-stabilized gold nanoclusters

This study presents a one-step approach to prepare lysozyme type VI-stabilized gold nanoclusters (Lys VI-AuNCs) for the ultrasensitive detection of Hg(2+) and CH(3)Hg(+) based on fluorescence quenching. The optical properties and size of Lys VI-AuNCs are highly dependent on the concentration of Lys VI, which acts as both a reducing and a stabilizing agent. With an increase in the concentration of Lys VI, we observed a systematic blue shift in the fluorescence maxima, an increase in the quantum yields, and a reduction in the particle size. When using 25 mg/mL Lys VI as a reducing agent, the formed Lys VI-AuNCs (denoted as Au-631) were found to be highly stable in a high-concentration glutathione or NaCl. Additionally, the Au-631 were capable of sensing Hg(2+) and CH(3)Hg(+) through the interaction between Hg(2+)/CH(3)Hg(+) and Au(+) on the Au surface; the limits of detection (LODs) for Hg(2+) and CH(3)Hg(+) were 3 pM and 4 nM, respectively. The selectivity of this probe is more than 500-fold for Hg(2+) over any metal ions. As compared to bovine serum albumin-stabilized AuNCs, Au-631 provided an approximately 330-fold improvement in the detection of Hg(2+). To the best of our knowledge, Au-631 not only provide the first example for detecting CH(3)Hg(+) but also have the lowest LOD value for Hg(2+) when compared to other AuNC-based Hg(2+) sensors. Importantly, this probe was successfully applied to the determination of Hg(2+) and CH(3)Hg(+) in seawater.     

Hydrodynamic chromatography online with single particle-inductively coupled plasma mass spectrometry for ultratrace detection of metal-containing nanoparticles

Nanoparticle (NP) determination has recently gained considerable interest since a growing number of engineered NPs are being used in commercial products. As a result, their potential to enter the environment and biological systems is increasing. In this study, we report on the development of a hyphenated analytical technique for the detection and characterization of metal-containing NPs, i.e., their metal mass fraction, size, and number concentration. Hydrodynamic chromatography (HDC), suitable for sizing NPs within the range of 5 to 300 nm, was coupled online to inductively coupled plasma mass spectrometry (ICPMS), providing for an extremely selective and sensitive analytical tool for the detection of NPs. However, a serious drawback when operating the ICPMS in its conventional mode is that it does not provide data regarding NP number concentrations and, thus, any information about the metal mass fraction of individual NPs. To address this limitation, we developed single particle (SP) ICPMS coupled online to HDC as an analytical approach suitable for simultaneously determining NP size, NP number concentration, and NP metal content. Gold (Au) NPs of various sizes were used as the model system. To achieve such characterization metrics, three calibrations were required and used to convert ICPMS signal spikes into NPs injected, NP retention time on the HDC column to NP size, and ions detected per signal spike or per NP to metal content in each NP. Two calibration experiments were required in order to make all three calibrations. Also, contour plots were constructed in order to provide for a convenient and most informative viewing of this data. An example of this novel analytical approach was demonstrated for the analysis of Au NPs that had been spiked into drinking water at the ng Au L(-1) level. The described technique gave limits of detection for 60 nm Au NPs of approximately 2.2 ng Au L(-1) or expressed in terms of NP number concentrations of 600 Au NPs mL(-1). These were obtained while the 60 nm NPs exhibited a retention time of 771 s at a mobile phase flow rate of 1 mL min(-1).     

Mercuric ion sensing by a film bulk acoustic resonator

This paper describes a film bulk acoustic resonator (FBAR) mass sensor for detecting Hg2+ ion in water with excellent sensitivity and selectivity. When a thin Au film was deposited on the surface of an FBAR, the resonant frequency shifted to a lower value when the film was exposed to Hg2+ in aqueous solution. The FBAR sensor detected as low as 10(-9) M Hg2+ (0.2 ppb Hg2+) in water. Other ions such as K+, Ca2+, Mg2+, Zn2+, and Ni2+ had little or no effect on the resonant frequency of the FBAR. Coating of the FBAR Au surface with a self-assembled monolayer (SAM) of 4-mercaptobenzoic acid decreased the Hg2+ response.     

Impedimetric immobilized DNA-based sensor for simultaneous detection of Pb2+, Ag+, and Hg2+

An unlabeled immobilized DNA-based sensor was reported for simultaneous detection of Pb(2+), Ag(+), and Hg(2+) by electrochemical impedance spectroscopy (EIS) with [Fe(CN)(6)](4-/3-) as redox probe, which consisted of three interaction sections: Pb(2+) interaction with G-rich DNA strands to form G-quadruplex, Ag(+) interaction with C-C mismatch to form C-Ag(+)-C complex, and Hg(2+) interaction with T-T mismatch to form T-Hg(2+)-T complex. Circular dichroism (CD) and UV-vis spectra indicated that the interactions between DNA and Pb(2+), Ag(+), or Hg(2+) occurred. Upon DNA interaction with Pb(2+), Ag(+), and Hg(2+), respectively, a decreased charge transfer resistance (R(CT)) was obtained. Taking advantage of the R(CT) difference (ΔR(CT)), Pb(2+), Ag(+), and Hg(2+) were selectively detected with the detection limit of 10 pM, 10 nM, and 0.1 nM, respectively. To simultaneously (or parallel) detect the three metal ions coexisting in a sample, EDTA was applied to mask Pb(2+) and Hg(2+) for detecting Ag(+); cysteine was applied to mask Ag(+) and Hg(2+) for detecting Pb(2+), and the mixture of G-rich and C-rich DNA strands were applied to mask Pb(2+) and Ag(+) for detecting Hg(2+). Finally, the simple and cost-effective sensor could be successfully applied for simultaneously detecting Pb(2+), Ag(+), and Hg(2+) in calf serum and lake water.     

Electrochemical DNAzyme sensor for lead based on amplification of DNA-Au bio-bar codes

An electrochemical DNAzyme sensor for sensitive and selective detection of lead ion (Pb(2+)) has been developed, taking advantage of catalytic reactions of a DNAzyme upon its binding to Pb(2+) and the use of DNA-Au bio-bar codes to achieve signal enhancement. A specific DNAzyme for Pb(2+) is immobilized onto an Au electrode surface via a thiol-Au interaction. The DNAzyme hybridizes to a specially designed complementary substrate strand that has an overhang, which in turn hybridizes to the DNA-Au bio-bar code (short oligonucleotides attached to 13 nm gold nanoparticles). A redox mediator, Ru(NH3)6(3+), which can bind to the anionic phosphate of DNA through electrostatic interactions, serves as the electrochemical signal transducer. Upon binding of Pb(2+) to the DNAzyme, the DNAzyme catalyzes the hydrolytic cleavage of the substrate, resulting in the removal of the substrate strand along with the DNA bio-bar code and the bound Ru(NH3)6(3+) from the Au electrode surface. The release of Ru(NH3)6(3+) results in lower electrochemical signal of Ru(NH3)6(3+) confined on the electrode surface. Differential pulse voltammetry (DPV) signals of Ru(NH3)6(3+) provides quantitative measures of the concentrations of Pb(2+), with a linear calibration ranging from 5 nM to 0.1 microM. Because each nanoparticle carries a large number of DNA strands that bind to the signal transducer molecule Ru(NH3)6(3+), the use of DNA-Au bio-bar codes enhances the detection sensitivity by five times, enabling the detection of Pb(2+) at a very low level (1 nM). The DPV signal response of the DNAzyme sensor is negligible for other divalent metal ions, indicating that the sensor is highly selective for Pb(2+). Although this DNAzyme sensor is demonstrated for the detection of Pb(2+), it has the potential to serve as a general platform for design sensors for other small molecules and heavy metal ions.     

Oligonucleotide-based fluorescence probe for sensitive and selective detection of mercury(II) in aqueous solution

In this paper we unveil a new homogeneous assayusing TOTO-3 and the polythymine oligonucleotide T 33for the highly selective and sensitive detection of Hg (2+) in aqueous solution. The fluorescence of TOTO-3 is weak in the absence or presence of randomly coiled T 33. After T 33 interacts specifically with Hg (2+) ions through T-Hg (2+)-T bonding, however, its conformation changes to form a folded structure that preferably binds to TOTO-3. As a result, the fluorescence of a mixture of T 33 and TOTO-3 increases in the presence of Hg (2+). Our data from fluorescence polarization spectroscopy, capillary electrophoresis with laser-induced fluorescence detection, circular dichroism spectroscopy, and melting temperature measurements confirm the formation of folded T 33-Hg (2+) complexes. Under optimum conditions, the TOTO-3/T 33 probe exhibited a high selectivity (>or=265-fold) toward Hg (2+) over other metal ions, with a limit of detection of 0.6 ppb. We demonstrate the practicality of this TOTO-3/T 33 probe for the rapid determination of Hg (2+) levels in pond water and in batteries. This approach offers several advantages, including rapidity (<15 min), simplicity (label-free), and low cost.     

Organic–inorganic hybrid mesoporous monoliths for selective discrimination and sensitive removal of toxic mercury ions

Abstract  

The selective optical sensing is attracting strong interest due to the use of “low-tech” spectroscopic instrumentation to detect relevant chemical species in biological and environmental processes. Our development has focused on tailoring specific solid mesoporous monoliths to be used as highly sensitive solid sensors for simple and simultaneous naked-eye detection and removal processes of extremely toxic heavy metal ions such as mercury ions in aquatic samples. The methods are emerging to design optical disc-like sensors by the immobilisation two different organic groups; however, the first organic moiety can enhance the polarity of the inorganic mesoporous disc-like monoliths “additional agents” and the second one can act as a recognition center “probe”. The latter one such as tetraphenylporphine tetrasulfonic acid (TPPS) probe led to facile handling of signal read-out with visual detection of ultra-trace concentrations of mercury ions at the same frequency as the human eye. The facile signaling was quantitatively evident using simple spectrophotometric techniques to indicate the TPPS–Hg(II) ion binding events. Control sensing assays of Hg(II) ions such as contact-time “signal response time”, thickness of support-based sensor, reaction temperature, and pH were established for achieving enhanced signal response and color intensities. Based on our results, these new classes of optical cage sensors exhibited long-term stability of recognition and signaling functionalities of Hg(II) ions that in general provided extraordinary sensitivity, selectivity, reusability, and fast kinetic detection and quantification of Hg(II) ions in our environment.     

Detection of mercury(II) by quantum dot/DNA/gold nanoparticle ensemble based nanosensor via nanometal surface energy transfer

An ultrasensitive fluorescent sensor based on the quantum dot/DNA/gold nanoparticle ensemble has been developed for detection of mercury(II). DNA hybridization occurs when Hg(II) ions are present in the aqueous solution containing the DNA-conjugated quantum dots (QDs) and Au nanoparticles. As a result, the QDs and the Au nanoparticles are brought into the close proximity, which enables the nanometal surface energy transfer (NSET) from the QDs to the Au nanoparticles, quenching the fluorescence emission of the QDs. This nanosensor exhibits a limit of detection of 0.4 and 1.2 ppb toward Hg(II) in the buffer solution and in the river water, respectively. The sensor also shows high selectivity toward the Hg(II) ions.     

Bifunctional fluoroionphore-ionic liquid hybrid for toxic heavy metal ions: improving its performance via the synergistic extraction strategy

Several heavy metal ions (HMIs), such as Cd(2+), Pb(2+), and Hg(2+), are highly toxic even at very low concentrations. Although a large number of fluoroionphores have been synthesized for HMIs, only a few of them show detection limits that are below the maximum contamination levels in drinking water (usually in the nM range), and few of them can simultaneously detect and remove HMIs. In this work, we report a new fluoroionphore-ionic liquid hybrid-based strategy to improve the performance of classic fluoroionphores via a synergistic extraction effect and realize simultaneous instrument-free detection and removal of HMIs. As a proof-of-concept, Hg(2+) was chosen as a model HMI, and a rhodamine thiospirolactam was chosen as a model fluoroionphore to construct bifunctional fluoroionphore-ionic liquid hybrid 1. The new sensing system could provide obviously improved sensitivity by simply increasing the aqueous-to-ionic liquid phase volume ratio to 10:1, resulting in a detection limit of 800 pM for Hg(2+), and afford extraction efficiencies larger than 99% for Hg(2+). The novel strategy provides a general platform for highly sensitive detection and removal of various HMIs in aqueous samples and holds promise for environmental and biomedical applications.     

"Molecular beacon"-based fluorescent assay for selective detection of glutathione and cysteine

We report on the development of a fluorescence turn-on "molecular beacon" probe for the detection of glutathione (GSH) and cysteine (Cys). The method is based on a competitive ligation of Hg(2+) ions by GSH/Cys and thymine-thymine (T-T) mismatches in a DNA strand of the self-hybridizing beacon strand. The assay relies on the distance-dependent optical properties of the fluorophore/quencher pair attached to the ends of the molecular beacon DNA strand. In a very selective coordination of Hg(2+) to GSH/Cys, the fluorophore/quencher distance increases concomitantly with the dehybridization and dissociation of the beacon stem T-Hg(2+)-T due to the extraction of Hg(2+) ions. This process results in switching the molecular beacon to the "on" state. The concentration range of the probe is 4-200 nM with the limit of detection (LOD) of 4.1 nM for GSH and 4.2 nM Cys. The probe tested satisfactorily against interference for a range of amino acids including sulfur-containing methionine.     

Magnetic bead-based chemiluminescent metal immunoassay with a colloidal gold label

A novel, sensitive chemiluminescent (CL) immunoassay has been developed by taking advantage of a magnetic separation/mixing process and the amplification feature of colloidal gold label. First, the sandwich-type complex is formed in this protocol by the primary antibody immobilized on the surface of magnetic beads, the antigen in the sample, and the second antibody labeled with colloidal gold. Second, a large number of Au3+ ions from each gold particle anchored on the surface of magnetic beads are released after oxidative gold metal dissolution and then quantitatively determined by a simple and sensitive Au3+-catalyzed luminol CL reaction. Third, this protocol is evaluated for a noncompetitive immunoassay of a human immunoglobulin G, and a concentration as low as 3.1 x 10(-12) M is determined, which is competitive with colloidal gold-based anodic stripping voltammetry (ASV), colorimetric ELISA, or immunoassays based on fluorescent europium chelate labels. The high performance of this protocol is related to the sensitive CL determination of Au3+ ion (detection limit of 2 x 10(-10) M), which is 25 times higher than that by ASV at a single-use carbon-based screen-printed electrode. From the analytical chemistry point of view, this protocol will be quite promising for numerous applications in immunoassay and DNA hybridization.