A reusable biosensor for detecting mercury(II) at the subpicomolar level based on "turn-on" resonance light scattering

A berberine induced disassembly towards zwitterionic surfactant as mimicking cell membrane for light-scattering sensing and logic devices

A label-free light-scattering sensor for berberine determination was developed based on Gemini zwitterionic surfactant as logic devices. Amphiphilic phosphodiesters quaternary ammonium nanoparticles (PQANPs) with bionic phosphate ester structure were selected as a model for mimicking cell membrane. PQANPs self-assembled and formed the micelle structure, emitting strong light-scattering signal. Interestingly, the addition of berberine induced remarkable decrease of light-scattering attribute to its interfering behavior of PQANPs aggregation. Disassembly of PQANPs could be triggered due to electrostatic interaction and hydrophobic force between PQANPs and berberine. The berberine attached to the PQANPs surface and generated nanocomposites, resulting in significant reduce of light-scattering signal. Hence, it generated a strong light-scattering signal variation according to the change of the concentration of target. Our proposed light-scattering on-off sensor could be applied for berberine detection with detection limit of 27 nM. Moreover, a logic gate system was constructed based on PQANPs sensor with berberine and the interfering substances as the inputs and the light-scattering intensity as an output, which could hold great potential application in future clinical diagnosis and drug analysis.

Visible-Light-Prompted Synthesis and Binding Studies of 5,6-Dihydroimidazo[2,1-b]thiazoles with BSA and DNA Using Biophysical and Computational Methods

Fused heterocyclic systems containing a bridgehead nitrogen atom have emerged as imperative pharmacophores in the design and development of new drugs. Among these heterocyclic moieties, the imidazothiazole scaffold has long been used in medicinal chemistry for the treatment of various diseases. In this study, we have established a simplistic and environmentally safe regioselective protocol for the synthesis of 5,6-dihydroimidazo[2,1-b]thiazole derivatives from easily available reactants. The reaction proceeds through in situ formation of the α-bromodiketones ensuing trap with imidazolidine-2-thione to provide these versatile bicyclic heterocycles in excellent yields. The synthesized compounds were screened through the molecular docking approach for the most stable complex formation with bovine serum albumin (BSA) and calf thymus deoxyribonucleic acid (ctDNA). The selected compound was further studied using ex vivo binding studies, which revealed moderate interactions with BSA and ctDNA. The binding studies were performed using biophysical approaches including UV-visible spectroscopy, steady-state fluorescence, circular dichroism (CD), and viscosity parameters.

A Highly Selective and Sensitive Peptide-Based Fluorescent Ratio Sensor for Ag. J Fluoresc 2020;31:237-246. [PMID: 33215317 DOI: 10.1007/s10895-020-02653-5]

A fluorescence ratio sensor based on dansyl-peptide, Dansyl-Glu-Cys-Glu-Glu-Trp-NH₂ (D-P5), was efficiently synthesized by Fmoc solid phase peptide synthesis. The sensor exhibits high selectivity and sensitivity for Ag⁺ over 16 metal ions in 100 mM sodium perchlorate and 50 mM 2-[4-(2-hydroxyethyl)piperazin-1-yl]ethanesulfonic acid buffer solution by fluorescence resonance energy transfer. The 1:1 binding stoichiometry of the sensor and Ag⁺ is measured by fluorescence ratio response and the job's plot. The dissociation constant of the sensor with Ag⁺ was calculated to be 6.4 × 10^-9 M, which indicates that the sensor has an effective binding affinity for Ag⁺. In addition, the limit of detection of the sensor for Ag⁺ was determined to be 80 nM, which also indicates that the sensor has a high sensitivity to Ag⁺. Result showed that the sensor is an excellent Ag⁺ sensor under neutral condition. Furthermore, this sensor displays good practicality for Ag⁺ detection in river water samples without performing tedious sample pretreatment, as well as for silver chloride detection.

Ultrasensitive determination of mercury ions using a glassy carbon electrode modified with nanocomposites consisting of conductive polymer and amino-functionalized graphene quantum dots

A one-pot method based on cyclic voltammetric scan was used to fabricate a glassy carbon electrode modified with nanocomposites consisting of poly(thionine) and amino-functionalized graphene quantum dots (afGQDs). Under near-neutral conditions, the dye polymer was effectively oxidized by hydroxyl radicals (·OH) that were derived from the copper-catalyzed Fenton-like reaction, and the cathodic peak current on the modified electrode greatly increased. The reaction of Cu²⁺ with thiourea (TU) and the generation of a complex, CuTU₂⁺, led to the decrease of Cu²⁺/Cu⁺ species, which inhibited the Fenton-like reaction and reduced the electrochemical response change. Due to a displacement reaction, the addition of Hg²⁺ into the H₂O₂-Cu²⁺-TU system resulted in the release of cuprous ions that benefited the Fenton-like reaction. Under the following optimal conditions: 6 mg mL^-1 afGQDs and the 25-cycle potential cycling for the fabrication of the modified electrode, pH 6.5, and the [Formula: see text] ratio of 1.0, the increasing extent of the cathodic peak current exhibited a good linear response to the logarithm of the Hg²⁺ concentration in the range of 1 pM-1 μM with a detection limit of 0.6 pM. Mercury ions in a water sample were determined with good recovery, ranging from 97 to 103%. The investigation on the uptake of Hg²⁺ into human vascular endothelial cells, HUVEC, shows that the cells incubated in the high-concentration glucose medium absorbed more mercury ions than HUVEC incubated in the normal medium. As a result, Hg²⁺ could lead to the greater damage to the former. Graphical abstract.

Multifunctional peptide-based fluorescent chemosensor for detection of Hg2+ , Cu2+ and S2- ions

A novel multifunctional fluorescent peptide sensor based on pentapeptide dansyl-Gly-His-Gly-Gly-Trp-COOH (D-P5) was designed and synthesized efficiently using Fmoc solid-phase peptide synthesis (SPPS). This fluorescent peptide sensor shows selective and sensitive responses to Hg²⁺ and Cu²⁺ among 17 metal ions and six anions studied in N-2-hydroxyethylpiperazine-N-2-ethane sulfonic acid (HEPES) buffer solution. The peptide probe differentiates Hg²⁺ and Cu²⁺ ions by a 'turn-on' response to Hg²⁺ and a 'turn-off' response to Cu²⁺ . Upon addition of Hg²⁺ or Cu²⁺ ions, the sensor displayed an apparent color change that was visible under an ultraviolet lamp to the naked eye. The limits of detection (LOD) of DP-5 were 25.0 nM for Hg²⁺ and 85.0 nM for Cu²⁺ ; the detection limits for Cu²⁺ were much lower than the drinking water maximum contaminant levels set out by the United States Environmental Protection Agency (USEPA). It is noteworthy that both D-P5-Hg and D-P5-Cu systems were also used to detect S^2- successfully based on the formation of ternary complexes. The LODs of D-P5-Hg and D-P5-Cu systems for S^2- were 217.0 nM and 380.0 nM, respectively. Furthermore, the binding stoichiometry, binding affinity and pH sensitivity of the probe for Hg²⁺ and Cu²⁺ were investigated. This study gives new possibilities for using a short fluorescent peptide sensor for multifunctional detection, especially for anions.

Phosphodiesters quaternary ammonium nanoparticles as label-free light scattering probe for turn-off detection of tyrosine

In this contribution, a new highly sensitive and selective sensor of the determination of tyrosine has been proposed based on the downturn effect of light scattering (LS) using phosphodiesters quaternary ammonium nanoparticles (PQANPs). Phosphodiesters quaternary ammonium (PQA), one of Gemini zwitterionic surfactants, self-aggregated into the micelle named as PQANPs, which generated strong LS signal in aqueous solution under the optimum condition. Interestingly, the powerful LS intensity of PQANPs with the maximum peak located at 391 nm significantly decreased after introducing trace amount of tyrosine. The decreased value of the LS intensity of the PQA-tyrosine system (ΔI_LS) was in proportion to tyrosine concentration in the ranges from 5.5 × 10^-8 mol/L to 4.68 × 10^-6 mol/L, with a detection limit of 1.38 × 10^-8 mol/L. Based on this decreased LS situation, the novel approach of the determination of tyrosine was first developed. The reaction mechanism for the interaction between PQANPs and tyrosine was also investigated. Moreover, the proposed LS assay was applied to the detection of tyrosine concentration in human serum and urine samples with satisfactory results.

Ultrasensitive impedimetric mercury(II) sensor based on thymine-Hg(II)-thymine interaction and subsequent disintegration of multiple sandwich-structured DNA chains

An impedimetric method is described for ultrasensitive analysis of mercury(II). It is based on thymine-Hg(II)-thymine interaction which causes the disintegration of multiple-sandwich structured DNA chains. DNA strands were selected that are partially complementary to the T-rich Hg(II)-specific oligonucleotides (MSO). They were immobilized on a gold electrode via Au-S interaction. Next, the MSO and the bridging strands (BS) that can connect adjacent MSOs were alternately attached through layer-by-layer hybridization. Thus, a multiple-sandwich structured interface in created that carries numerous MSOs. This leads to a change-transfer resistance (R_ct) values of the electrode-electrolyte interface at faradic electrochemical impedance spectroscopy measurements in the presence of the hexacyanoferrate(II)/(III) redox probe at 0.2 V (vs. Ag/AgCl). If Hg(II) is added to the solution, the MSOs selectively interact with Hg(II) to produce T-Hg(II)-T structures. Hence, the multiple-sandwich hybridization chains become disintegrated, and this causes a decrease in resistivity. The effect can be used to quantify Hg(II) over an analytical range that extends over four orders of magnitude (1 fM to 10 pM), and it has a 0.16 fM limit of detection under optimal conditions. Graphical abstract An electrochemical sensor for femtomolar level detection of Hg²⁺ is realized on the basis of thymine-Hg²⁺-thymine interaction which causes disintegration of multiple sandwich DNA hybridization strands.

Resonance light scattering aptasensor for urinary 8-hydroxy-2'-deoxyguanosine based on magnetic nanoparticles: a preliminary study of oxidative stress association with air pollution

An aptamer based method is described for the determination of 8-hydroxy-2'-deoxyguanosine (8-OHdG) using resonance light scattering (RLS). Magnetic nanoparticles (MNPs) were employed as RLS probes. The probe DNA was placed on the surface of MNPs, which produces a rather low RLS signal. If, however, probe DNA hybridizes with the aptamer against 8-OHdG, a sandwich structure will be formed. This results in a significant enhancement of RLS intensity. The aptamer was used as the recognition element to capture 8-OHdG. 8-OHdG has a stronger affinity for the aptamer than probe DNA, and the conformation of the aptamer therefore switches from a double-stranded to a G-quadruplex structure. As a result, MNPs labeled with probe DNA are released, and RLS intensity decreases. The method allows 8-OHdG to be detected with a linear response in the 32 pM - 12.0 nM concentration range and an 11 pM limit of detection (at 3.29S_B/m, according to the recent recommendation of IUPAC). The MNPs can be reused 5 times by applying an external magnetic field for collection. The method was successfully applied to analyze human urine samples for its content of 8-OHdG. It was also found that the levels of 8-OHdG noticeably increased with the increase of the Air Quality Index. Conceivably, the method is a viable tool to investigate the relationship between 8-OHdG levels and the effect of air pollution. Graphical abstract A reusable sensing strategy was constructed to detect urinary 8-OHdG based on "turn-off" resonance light scattering. The LOD was as low as 11 pM. This study showed some preliminary data for the association between oxidative stress and air pollution.

A peptide-based multifunctional fluorescent probe for Cu2+, Hg2+ and biothiols

A peptide-based fluorescent probe (Dansyl-His-Pro-Gly-Trp-NH₂, D-P4) bearing the dansyl fluorophore and tryptophan residue has been developed for the detection of Hg²⁺, Cu²⁺ and biothiols (–SH).

Development of paper-based chemosensor for the detection of mercury ions using mono- and tetra-sulfur bearing phenanthridines

A new sulfur-bearing phenanthridine probes were synthesized and examined for their cation recognition abilities towards different cations in aqueous ACN solution and paper strips.

High-performance liquid chromatography study of gatifloxacin and sparfloxacin using erythrosine as post-column resonance Rayleigh scattering reagent and mechanism study

Herein, a highly selective high-performance liquid chromatography (HPLC) coupled with resonance Rayleigh scattering (RRS) method was developed to detect gatifloxacin (GFLX) and sparfloxacin (SPLX). GFLX and SPLX were first separated by HPLC, then, in pH 4.4 Britton-Robinson (BR) buffer medium, protonic quaternary ammonia cation of GFLX and SPLX reacted with erythrosine (ERY) to form 1:1 ion-association complexes, which resulted in a significant enhancement of RRS signal. The experimental conditions of HPLC and post-column RRS have been investigated, including detection wavelength, flow rate, pH, reacting tube length and reaction temperature. Reaction mechanism were studied in detail by calculating the distribution fraction. The maximum RRS signals for GFLX and SPLX were recorded at λ_ex  = λ_em  = 330 nm. The detection limits were 3.8 ng ml^-1 for GFLX and 17.5 ng ml^-1 for SPLX at a signal-to-noise ratio of 3. The developed method was successfully applied to the determination of GFLX and SPLX in water samples. Recoveries from spiked water samples were 97.56-98.85%.

In-situ formation of ion-association nanoparticles induced enhancements of resonance Rayleigh scattering intensities for quantitative analysis of trace Hg(2+) ions in environmental samples

In this paper, Hg(2+) ions are demonstrated to form anionic [HgI4](2-) complexes after interacting with massive amount of I(-) ions. Subsequently, the addition of tetradecyl pyridyl bromide (TPB) can make [HgI4](2-) anionic complexes react with univalent tetradecyl pyridyl cationic ions (TP(+)), forming dispersed ion-association complexes (TP)2(HgI4). Due to the extrusion action of water and Van der Waals force, the hydrophobic ion-association complexes aggregate together, forming dispersed nanoparticles with an average size of about 8.5nm. Meanwhile, resonance Rayleigh scattering (RRS) intensity is apparently enhanced due to the formation of (TP)2(HgI4) ion-association nanoparticles, contributing to a novel technique for Hg(2+) detection. The wavelength of 365nm is chosen as a detection wavelength and several conditions affecting the RRS responses of Hg(2+) are optimized. Under the optimum condition, the developed method is used for the determination of Hg(2+) in aqueous solution and the detection limit is estimated to be 0.8ngmL(-1). Finally, the practical application of the developed method can be confirmed through the detections of Hg(2+) in waste and river water samples with satisfactory results.

Optical Aptasensors for Adenosine Triphosphate

Nucleic acids are among the most researched and applied biomolecules. Their diverse two- and three-dimensional structures in conjunction with their robust chemistry and ease of manipulation provide a rare opportunity for sensor applications. Moreover, their high biocompatibility has seen them being used in the construction of in vivo assays. Various nucleic acid-based devices have been extensively studied as either the principal element in discrete molecule-like sensors or as the main component in the fabrication of sensing devices. The use of aptamers in sensors - aptasensors, in particular, has led to improvements in sensitivity, selectivity, and multiplexing capacity for a wide verity of analytes like proteins, nucleic acids, as well as small biomolecules such as glucose and adenosine triphosphate (ATP). This article reviews the progress in the use of aptamers as the principal component in sensors for optical detection of ATP with an emphasis on sensing mechanism, performance, and applications with some discussion on challenges and perspectives.

Synthesis, optical, and chemical properties of a π-extended rhodol derivative and its derivatives with selectivity and sensitivity for sensing Hg2+in aqueous media

A π-extended rhodol dye with optical signaling being controlled by two spirorings has been developed. A Hg²⁺-selective chemodosimeter based on this rhodol dye has been synthesized and evaluated.

Modern affinity reagents: Recombinant antibodies and aptamers

Affinity reagents are essential tools in both basic and applied research; however, there is a growing concern about the reproducibility of animal-derived monoclonal antibodies. The need for higher quality affinity reagents has prompted the development of methods that provide scientific, economic, and time-saving advantages and do not require the use of animals. This review describes two types of affinity reagents, recombinant antibodies and aptamers, which are non-animal technologies that can replace the use of animal-derived monoclonal antibodies. Recombinant antibodies are protein-based reagents, while aptamers are nucleic-acid-based. In light of the scientific advantages of these technologies, this review also discusses ways to gain momentum in the use of modern affinity reagents, including an update to the 1999 National Academy of Sciences monoclonal antibody production report and federal incentives for recombinant antibody and aptamer efforts. In the long-term, these efforts have the potential to improve the overall quality and decrease the cost of scientific research.

Resonance light scattering detection of fructose bisphosphates using uranyl-salophen complex-modified gold nanoparticles as optical probe

In this paper, we report a resonance light scattering (RLS) method for the determination of fructose bisphosphates (FBPs) in water solution using fructose 1,6-bisphosphate (F-1,6-BP) as a model analyte without the procedure of extracting target analyte. The method used a type of modified gold nanoparticles (GNPs) as optical probe. The modified GNPs are uranyl-salophen-cysteamine-GNPs (U-Sal-Cy-GNPs) which are obtained through the acylation reaction of carboxylated salophen with cysteamine-capped GNPs (Cy-GNPs) to form Sal-Cy-GNPs and then the chelation reaction of uranyl with tetradentate ligand salophen in the Sal-Cy-GNPs. A FBP molecule is used easily to connect two U-Sal-Cy-GNPs to cause the aggregation of the GNPs by utilizing the specific affinity of uranyl-salophen complex to phosphate group, resulting in the production of strong RLS signal from the system. The amount of FBPs can be determined through detecting the RLS intensity change of the system. A linear range was found to be 2.5 to 75 nmol/L with a detection limit of 0.91 nmol/L under optimal conditions. The method has been successfully used to determine FBPs in real samples with the recoveries of 96.5-103.5 %.

Functional nucleic acid-based sensors for heavy metal ion assays

Heavy metal contaminants such as lead ions (Pb(2+)), mercury ions (Hg(2+)) and silver ions (Ag(+)) can cause significant harm to humans and generate enduring bioaccumulation in ecological systems. Even though a variety of methods have been developed for Pb(2+), Hg(2+) and Ag(+) assays, most of them are usually laborious and time-consuming with poor sensitivity. Due to their unique advantages of excellent catalytic properties and high affinity for heavy metal ions, functional nucleic acids such as DNAzymes and aptamers show great promise in the development of novel sensors for heavy metal ion assays. In this review, we summarize the development of functional nucleic acid-based sensors for the detection of Pb(2+), Hg(2+) and Ag(+), and especially focus on two categories including the direct assay and the amplification-based assay. We highlight the emerging trends in the development of sensitive and selective sensors for heavy metal ion assays as well.

Fluorescent detection of Hg2+ and Pb2+ using GeneFinder™ and an integrated functional nucleic acid

This paper reports a simple fluorescent assay for the determination of Hg(2+) and Pb(2+) by using a DNA intercalator GeneFinder™ (GF) and an integrated functional nucleic acid (FNA). In the absence of Hg(2+) and Pb(2+), GF intercalated with the FNA and released moderate strong fluorescence. While in the presence of Hg(2+) or Pb(2+), the FNA would be induced to form T-Hg(2+)-T or G-quadruplex structure, interacted with which the GF would exhibit extremely strong or very weak fluorescence. By monitoring the fluorescence changes upon addition of these two ions, the Hg(2+) and Pb(2+) could be selectively detected as low as 3.23 ppb and 2.62 ppb. As the main advantage of this assay is simplicity and the feasibility was demonstrated by detecting Hg(2+) and Pb(2+) in spiked water samples, this assay holds great potential for the development of a cost effective and useful tool for environmental monitoring.

A novel biosensor for copper(ii) ions based on turn-on resonance light scattering of ssDNA templated silver nanoclusters

A new ultrasensitive biosensor for copper(ii) ions was first developed based on turn-on resonance light scattering (RLS) of ssDNA templated silver nanoclusters through anti-galvanic reduction (AGR).

Electrochemical DNA sensor for specific detection of picomolar Hg(ii) based on exonuclease III-assisted recycling signal amplification

An ultrasensitive methodology was successfully developed for the quantitative detection of picomolar Hg²⁺ based on the combination of thymine–Hg²⁺–thymine (T–Hg²⁺–T) coordination chemistry and exonuclease III-aided recycling signal amplification.

A convenient sandwich assay of thrombin in biological media using nanoparticle-enhanced fluorescence polarization

A new aptamer biosensor was presented for the detection of thrombin in this work, which was based on fluorescence polarization (FP) using silica nanoparticles as enhancement probe. The silica nanoparticles covered by streptavidin were tagged with a thrombin aptamer (5'-biotin-GGTTGGTGTGGTTGG-3'), which was bound to the surface of silica nanoparticle through the specific interaction between streptavidin and biotin. In the presence of thrombin, it induced the aptamer to form quadruplex structure. When the other thrombin aptamer labeled with fluorescein (5'-FAM-AGTCCGTGGTAGGGCAGGTTGGGGTGACT-3') was added to the above system, a sandwich structure can form at the surface of silica nanoparticles. The fluorescence polarization was therefore enhanced and quantification between fluorescence polarization signal and concentration of thrombin was built. The sensor provided a linear range from 0.6 to 100 nM for thrombin with a detection limit of 0.20 nM (3.29 SB/m, according to the recent recommendation of IUPAC) in a homogeneous media. The same linear range was obtained in spiked human serum samples with a slightly higher detection limit (0.26 nM), demonstrating high anti-interference of the sensor in a complex biological sample matrix. And the sensor can be used to monitor spiked concentration of thrombin level in real human plasma with satisfactory results obtained.

Resonance light scattering determination of trace bisphenol A with signal amplification by aptamer-nanogold catalysis

HAuCl4 was reduced by sodium citrate to prepare 10 nm gold nanoparticles (AuNPs) that were modified by the bisphenol A aptamer (Apt) to obtain an aptamer-nanogold probe (Apt-AuNP) for bisphenol A (BPA). The probes were aggregated nonspecifically to form large clusters, which showed a strong resonance light scattering (RLS) peak at 520 nm, under preparation conditions (pH 7.6 Na2HPO4-NaH2PO4 buffer and ultrasonication). Upon addition of BPA, the probe reacted specifically to form dispersed BPA-Apt-AuNP conjugates that exhibited strong catalysis of the two particle reactions of glucose-Cu(II) and hydrazine hydrochloride-Cu(II) with a strong RLS peak at 360 nm and 510 nm respectively. When the BPA concentration increased, the RLS intensity at 360 nm and 510 nm increased respectively. Accordingly, two new and highly-sensitive RLS methods were established for the detection of BPA, using the Apt-AuNP catalytic amplification.

A reusable and sensitive biosensor for total mercury in canned fish based on fluorescence polarization

In this work, we developed a sensitive and selective sensor technique for total mercury (Hg) detection in canned fish samples based on the fluorescence polarization (FP) method. The detection principle was that ssDNA containing thymine (T) bases was modified on magnetic nanoparticles (MNPs), which were used as enhancement probe. In the presence of Hg(2+), the ssDNA on MNPs can hybridize with the fluorophore labeled aptamer owing to the specific interaction between T bases and Hg(2+). The formation of thymine-Hg(2+)-thymine (T-Hg(2+)-T) complexes leads to the molar mass increase of fluorophore molecules, resulting in the enhancement of FP signal. The increase of FP was in a good linearity with the concentration of Hg(2+) in range of 2.0 nM-1.0 mM and the limit of detection was 0.49 nM (3.29 SB/m, according to the recent recommendation of IUPAC). Moreover, the proposed biosensor can be reused for 6 cycling times and was successfully applied in monitoring Hg(2+) in real samples.