Detection of heavy metal ions at femtomolar levels using protein-based biosensors

Validation and calibration of a novel GEM biosensor for specific detection of Cd2+, Zn2+, and Pb2

BACKGROUND

In this study, we designed a novel genetic circuit sensitive to Cd2+, Zn2+ and Pb2+ by mimicking the CadA/CadR operon system mediated heavy metal homeostasis mechanism of Pseudomonas aeruginosa. The regular DNA motifs on natural operon were reconfigured and coupled with the enhanced Green Fluorescent Protein (eGFP) reporter to develop a novel basic NOT type logic gate CadA/CadR-eGFP to respond metal ions mentioned above. A Genetically Engineered Microbial (GEM)-based biosensor (E.coli-BL21:pJET1.2-CadA/CadR-eGFP) was developed by cloning the chemically synthesised CadA/CadR-eGFP gene circuit into pJET1.2-plasmid and transforming into Escherichia coli (E. coli)-BL21 bacterial cells.

RESULTS

The GEM-based biosensor cells indicated the reporter gene expression in the presence of Cd2+, Zn2+ and Pb2+ either singly or in combination. Further, the same biosensor cells calibrated for fluorescent intensity against heavy metal concentration generated linear graphs for Cd2+, Zn2+ and Pb2+ with the R2 values of 0.9809, 0.9761 and 0.9758, respectively as compared to non-specific metals, Fe3+ (0.0373), AsO43- (0.3825) and Ni2+ (0.8498) making our biosensor suitable for the detection of low concentration of the former metal ions in the range of 1-6 ppb. Furthermore, the GEM based biosensor cells were growing naturally within the concentration range of heavy metals, at 37 °C and optimum pH = 7.0 in the medium, resembling the characteristics of wildtype E.coli.

CONCLUSION

Finally, the novel GEM based biosensor cells developed in this study can be applied for detection of targeted heavy metals in low concentration ranges (1-6 ppb) at normal bacterial physiological conditions.

A designed miniature sensor for the trace level detection and degradation studies of the toxic dye Rhodamine B

The presence of organic pollutants in water and food samples is a risk for the environment. To avoid this hazard a variety of analytical tools are used for the detection of toxic organic contaminants. Herein we present a selective and sensitive electrochemical sensor based on amino group functionalized multi walled carbon nanotubes and carboxylic group functionalized multi walled carbon nanotubes (HOOC-fMWCNTs/NH2-fMWCNTs) as modifiers of the glassy carbon electrode for the detection of a toxic dye, Rhodamine B. The sensing ability of the designed sensor was examined by electrochemical impedance spectroscopy, cyclic voltammetry and square wave voltammetry. The synergistic effect of HOOC-fMWCNTs and NH2-fMWCNTs (layer by layer) led to enhanced electrocatalytic activity of the modified electrode surface for Rhodamine B detection. Under optimized conditions, the graph between concentration and peak current followed a linear trend in the concentration range of 0.1 nM to 0.05 μM. The limits of detection and quantification were found to be 57.4 pM and 191.3 pM respectively. The designed sensor was also used for probing the degradation of Rhodamine B. Sodium borohydride was found to degrade Rhodamine B in neutral media under ambient conditions. The kinetics of degradation followed first order kinetics. Rhodamine B degraded to the extent of more than 80% as revealed by electrochemical and spectrophotometric techniques. The developed method is promising for the treatment of dye contaminated wastewater. Moreover, it uses only a microliter volume of the sample for analysis.

Determination of deferasirox (anti-thalassemia drug) in serum and urine: cyclic voltammetry study

The purpose of this project is to examine cyclic voltammetry (CV) analytical technique for anti_thalassemia drug of deferasirox by modified multi-walled carbon nanotubes (MWCNTs) on glassy carbon electrod (GCE) was described. The electrochemical performance of deferasirox was studied by cyclic voltammetry technique. The ability of the electrode for the determination of deferasirox under Optimize condition in pH 13.8~14, scan rate 100mv/s, temperature 30 0C and interference that have been studied. Where found the results that calibration curve of deferasirox was linear in the concentrations 13.4×10-4-2.6×10-2 M, its detection limit was 8.46×10-11 M and LOQ was 2.82×10-10 M. The enthalpy ∆H was calculated to be (6.736 kJ. mol-1), and the entropy can be calculated to be (213.8 J. K‐1 mol‐1). The area of electrode was calculated to be 0.314 cm2 and also the diffusion coefficient was 3.154×10-4 cm2sec-1. RSD% for bulk and form was less than 0.3% while serum and urine less than 2.5% and recovery in all close to 100.1%. The voltammogram for deferasirox give irreversible process with diffusion– controlled process.  Finally, this technique has been applied for deferasirox on pharmaceutical formulations and biological samples (serum and urine).

Myeloperoxidase-induced fibrinogen unfolding and clotting

Due to its unique properties and high biomedical relevance fibrinogen is a promising protein for the development of various matrixes and scaffolds for biotechnological applications. Fibrinogen molecules may form extensive clots either upon specific cleavage by thrombin or in thrombin-free environment, for example, in the presence of different salts. Here, we report the novel type of non-conventional fibrinogen clot formation, which is mediated by myeloperoxidase and takes place even at low fibrinogen concentrations (<0.1 mg/ml). We have revealed fibrillar nature of myeloperoxidase-mediated fibrinogen clots, which differ morphologically from fibrin clots. We have shown that fibrinogen clotting is mediated by direct interaction of myeloperoxidase molecules with the outer globular regions of fibrinogen molecules followed by fibrinogen unfolding from its natural trinodular to a fibrillar structure. We have demonstrated a major role of the Debye screening effect in regulating of myeloperoxidase-induced fibrinogen clotting, which is facilitated by small ionic strength. While fibrinogen in an aqueous solution with myeloperoxidase undergoes changes, the enzymatic activity of myeloperoxidase is not inhibited in excess of fibrinogen. The obtained results open new insights into fibrinogen clotting, give new possibilities for the development of fibrinogen-based functional biomaterials, and provide the novel concepts of protein unfolding.

Revealing protein binding affinity on metal surfaces: an electrochemical approach

Revealing the binding affinity between viruses and surfaces of environmental matrices is crucial to evaluate the bioactivity of an immobilized virus and accompanying indirect virus-related infection pathways. The understanding for SARS-CoV-2 remaining infective for even days on stainless steel but only hours on copper is still unclear. Electrochemical chronoamperometry, ultrasensitive to interfacial capacitance on surface species, was used to investigate the binding affinity of SARS-CoV-2 on metal surfaces. S_RBD, the surrogate of SARS-CoV-2, shows the highest adsorption capacity on a gold surface, followed by Cu, but lowest on a stainless steel surface. The strong binding of S_RBD on copper is a result of the naturally grown Cu₂O under ambient conditions. Measurement of electrochemical capacitance provides a simple strategy to explore and evaluate the potential risk of an indirect virus-related infection pathway through conductive environmental matrices.

Critical review on hazardous pollutants in water environment: Occurrence, monitoring, fate, removal technologies and risk assessment

Water is required for the existence of all living things. Water pollution has grown significantly, over the decades and now it has developed as a serious worldwide problem. The presence and persistence of Hazardous pollutants such as dyes, pharmaceuticals and personal care products, heavy metals, fertilizer and pesticides and their transformed products are the matter of serious environmental and health concerns. A variety of approaches have been tried to clean up water and maintain water quality. The type of pollutants present in the water determines the bulk of technological solutions. The main objective of this article was to review the occurrences and fate of hazardous contaminants (dyes, pharmaceuticals and personal care products, heavy metals, and pesticides) found in wastewater effluents. These effluents mingle with other streams of water and that are utilized for a variety of reasons such as irrigation and other domestic activities that is further complicating the issue. It also discussed traditional treatment approaches as well as current advances in hazardous pollutants removal employing graphite oxides, carbon nanotubes, metal organic structures, magnetic nano composites, and other innovative forms of useable materials. It also discussed the identification and quantification of harmful pollutants using various approaches, as well as current advancements. Finally, a risk assessment of hazardous pollutants in water is provided in terms of the human health and the environment. This data is anticipated to serve as a foundation for future improvements in hazardous pollutant risk assessment. Furthermore, future studies on hazardous pollutants must not only emphasize on the parent chemicals, as well as on their possible breakdown products in various media.

Recent Advancements in Electrochemical Biosensors for Alzheimer's Disease Biomarkers Detection

Background

It is estimated that the average time between the diagnosis of Alzheimer’s disease (AD) and the patient’s death is 5-9 years. Therefore, both the initial phase of the disease and the preclinical state can be included in the critical period in disease diagnosis. Accordingly, huge progress has recently been observed in biomarker research to identify risk factors for dementia in older people with normal cognitive functions and mild cognitive impairments.

Methods

Electrochemical biosensors are excellent analytical tools that are used in the detection of AD biomarkers as they are easy to use, portable, and can do analysis in real time.

Results

This review presents the analytical techniques currently used to determine AD biomarkers in terms of their advantages and disadvantages; the most important clinical biomarkers of AD and their role in the disease. All recently used biorecognition molecules in electrochemical biosensor development, i.e., receptor protein, antibodies, aptamers and nucleic acids, are summarized for the first time. Novel electrochemical biosensors for AD biomarker detection, as ideal analytical platforms for point-of-care diagnostics, are also reviewed.

Conclusion

The article focuses on various strategies of biosensor chemical surface modifications to immobilize biorecognition molecules, enabling specific, quantitative AD biomarker detection in synthetic and clinical samples. In addition, this is the first review that presents innovative single-platform systems for simultaneous detection of multiple biomarkers and other important AD-associated biological species based on electrochemical techniques. The importance of these platforms in disease diagnosis is discussed.

Reusable Cyclodextrin-Based Electrochemical Platform for Detection of trans-Resveratrol

A reusable sensor architecture, through the combination of self-assembled monolayers and cyclodextrin supramolecular interactions, is demonstrated for class recognition of hydrophobic analytes demonstrated with trans-resveratrol. The reloadable sensor is based on reversible immobilization of α-cyclodextrin on polyethylene glycol surface. α-cyclodextrins complexes with polyethylene glycols and causes the polymer chains to change their surface configuration. The reproducibility and stability of the sur-face, in the detection of nanomolar concentrations of trans-resveratrol, can be demonstrated by electrochemical impedance spectroscopy, X-ray photoelectron spectroscopy, and Attenuated total reflectance-Fourier transform infrared spectroscopy. We propose that during sensor operation, α-cyclodextrin decouples from the poly-ethylene glycol surface to complex with trans-resveratrol in solution, and after use, the surface regeneration is conducted with a simple α-cyclodextrin soak. To test the nonspecific response, the sensor was also tested with trans-resveratrol spiked human urine.

Determination of (Bio)-available mercury in soils: A review

Despite the mercury (Hg) control measures adopted by the international community, Hg still poses a significant risk to ecosystem and human health. This is primarily due to the ability of atmospheric Hg to travel intercontinentally and contaminating terrestrial and aquatic environments far from its natural and anthropogenic point sources. The issue of Hg pollution is further complicated by its unique physicochemical characteristics, most noticeably its multiple chemical forms that vary in their toxicity and environmental mobility. This meant that most of the risk evaluation protocols developed for other metal(loid)s are not suitable for Hg. Soil is a major reservoir of Hg and a key player in its global cycle. To fully assess the risks of soil Hg it is essential to estimate its bioavailability and/or availability which are closely linked to its toxicity. However, the accurate determination of the (bio)-available pools of Hg in soils is problematic, because the terms 'bioavailable' and 'available' are ill-defined. In particular, the term 'bioavailable pool', representing the fraction of Hg that is accessible to living organisms, has been consistently misused by interchanging with other intrinsically different terms e.g. mobile, labile, reactive and soluble pools. A wide array of physical, chemical, biological and isotopic exchange methods were developed to estimate the (bio)-available pools of Hg in soil in an attempt to offer a plausible assessment of its risks. Unfortunately, many of these methods do not mirror the (bio)-available pools of soil Hg and suffer from technical drawbacks. In this review, we discuss advantages and disadvantages of methods that are currently applied to quantify the (bio)-availability of Hg in soils. We recommended the most feasible methods and give suggestions how to improve the determination of (bio)-available Hg in soils.

A natural cyanobacterial protein C-phycoerythrin as an Hg2+ selective fluorescent probe in aqueous systems

C-phycoerythrin (CPE) as a natural protein-based fluorescence ‘turn off’ probe for Hg²⁺ in aqueous systems.

Bio-modified carbon paste electrode for the detection of Pb(II) ions in wastewater

Heavy metal pollution in water is a serious environmental concern. Lead is one of the highly toxic heavy metals, and its toxicity is due to its non-degradation characteristic in living organisms. The monitoring of Pb(II) ions concentrations in drinking water is essential for human health and a safe environment. In this work, bio-modified carbon paste electrodes were constructed with live cells and thermally dried biomass (extracted protein) from Pseudomonas aeruginosa cells and employed for the detection of Pb(II) ions from wastewater. The biomass and biosensor preparation and optimization, and the performance of modified biosensors in the detection of Pb(II) ions are discussed here. The effect of various parameters, like pH, biomass composition, scan rate, and metal ion concentration, were studied to obtain the best electrochemical response. Further, the active surface of the electrode and solution characteristics were studies using chronocoulometry and electrochemical impedance spectroscopy. Fourier transform infrared spectroscopy (FTIR) analysis was done to find the functional groups present in the thermally dried biomass. From the present study, it is clear that the thermally dried protein biomass electrode has more sensitivity than the bare carbon paste electrode.

Cry Protein Crystal-Immobilized Metallothioneins for Bioremediation of Heavy Metals from Water

Cry proteins have been the subject of intense research due to their ability to form crystals naturally in Bacillus thuringiensis (Bt). In this research we developed a new strategy that allows for the removal of cadmium and chromium from wastewater by using one Cry protein, Cry3Aa, as a framework to immobilize tandem repeats of the cyanobacterial metallothionein SmtA from Synechococcus elongatus (strain PCC 7942). SmtA is a low molecular weight cysteine-rich protein known to bind heavy metals. A series of Cry3Aa-SmtA constructs were produced by the fusion of one, three, or six tandem repeats of SmtA to Cry3Aa. Overexpression of these constructs in Bt resulted in the production of pure Cry3Aa-SmtA fusion crystals that exhibited similar size, crystallinity, and morphology to that of native Cry3Aa protein crystals. All three Cry3Aa-SmtA constructs exhibited efficient binding to cadmium and chromium, with the binding capacity correlated with increasing SmtA copy number. These results suggest the potential use of Cry3Aa-SmtA crystals as a novel biodegradable and cost-effective approach to the removal of toxic heavy metals from the environment.

Fluorescent electronic tongue based on soluble conjugated polymeric nanoparticles for the discrimination of heavy metal ions in aqueous solution

A fluorescence sensing array (or fluorescent electronic tongue) based on six sorts of soluble conjugated polymeric nanoparticles (SCPNs) decorated with PEG chains is designed for the rapid identification of heavy metal ions in water.

pH Controlled Impedimetric Sensing of Copper(II) Ion Using Oxytocin as Recognition Element

We report the modulation of the specific metal gation properties of a peptide and demonstrate a highly selective sensor for copper(II) ion. The neuropeptide oxytocin (OT) is reported for its high affinity towards Zn2+ and Cu2+ at physiological pH. The binding of the metal ions to OT is tuned by altering the pH of the medium. OT was self-assembled on glassy carbon electrode using surface chemistry, and electrochemical impedance spectroscopy (EIS) was used to probe the binding of Cu2+. Our results clearly indicate that at pH 10.0, the binding of Cu2+ to OT is increased compared to that at pH 7.0, while the binding to Zn2+ becomes almost negligible. This proves that the selectivity of OT towards each of the ions can be regulated simply by controlling the pH of the medium and hence allows the preparation of a sensing device with selectivity to Cu2+.

Ultrasensitive interdigitated capacitance immunosensor using gold nanoparticles

Immunosensors based on interdigitated electrodes (IDEs), have recently demonstrated significant improvements in the sensitivity of capacitance detection. Herein, a novel type of highly sensitive, compact and portable immunosensor based on a gold interdigital capacitor has been designed and developed for the rapid detection of hepatitis B surface antigen (HBsAg). To improve the efficiency of antibody immobilization and time-saving, a self-assembled monolayer (SAM) of 2-mercaptoethylamine film was coated on IDEs. Afterwards, carboxyl groups on primary antibodies were activated through 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and were immobilized on amino-terminated SAM for better control of the oriented immobilization of antibodies on gold IDEs. In addition, gold nanoparticles conjugated with a secondary antibody were used to enhance the sensitivity. Under optimal conditions, the immunosensor exhibited the sensitivity of 0.22 nF.pg ml^-1, the linear range from 5 pg ml^-1 to 1 ng ml^-1 and the detection limit of 1.34 pg ml^-1, at a signal-to-noise ratio of 3.

Sensing of heavy metal ions by intrinsic TMV coat protein fluorescence

We propose the use of a cysteine mutant of TMV coat protein as a signal transducer for the selective sensing and quantification of the heavy metal ions, Cd²⁺, Pb²⁺, Zn²⁺ and Ni²⁺ based on intrinsic tryptophan quenching. TMV coat protein is inexpensive, can be mass-produced since it is expressed and extracted from E-coli. It also displays several different functional groups, enabling a wide repertoire of bioconjugation chemistries; thus it can be easily integrated into functional devices. In addition, TMV-ion interactions have been widely reported and utilized for metallization to generate organic-inorganic hybrid composite novel materials. Building on these previous observations, we herein determine, for the first time, the TMV-ion binding constants assuming the static fluorescence quenching model. We also show that by comparing TMV-ion interactions between native and denatured coat protein, we can distinguish between chemically similar heavy metal ions such as cadmium and zinc ions.

Oxytocin-Monolayer-Based Impedimetric Biosensor for Zinc and Copper Ions

Zinc and copper are essential metal ions for numerous biological processes. Their levels are tightly maintained in all body organs. Impairment of the Zn²⁺ to Cu²⁺ ratio in serum was found to correlate with many disease states, including immunological and inflammatory disorders. Oxytocin (OT) is a neuropeptide, and its activity is modulated by zinc and copper ion binding. Harnessing the intrinsic properties of OT is one of the attractive ways to develop valuable metal ion sensors. Here, we report for the first time an OT-based metal ion sensor prepared by immobilizing the neuropeptide onto a glassy carbon electrode. The developed impedimetric biosensor was ultrasensitive to Zn²⁺ and Cu²⁺ ions at physiological pH and not to other biologically relevant ions. Interestingly, the electrochemical impedance signal of two hemicircle systems was recorded after the attachment of OT to the surface. These two semicircles suggest two capacitive regions that result from two different domains in the OT monolayer. Moreover, the change in the charge-transfer resistance of either Zn²⁺ or Cu²⁺ was not similar in response to binding. This suggests that the metal-dependent conformational changes of OT can be translated to distinct impedimetric data. Selective masking of Zn²⁺ and Cu²⁺ was used to allow for the simultaneous determination of zinc to copper ions ratio by the OT sensor. The OT sensor was able to distinguish between healthy control and multiple sclerosis patients diluted sera samples by determining the Zn/Cu ratio similar to the state-of-the-art techniques. The OT sensor presented herein is likely to have numerous applications in biomedical research and pave the way to other types of neuropeptide-derived sensors.

General Signal Amplification Strategy for Nonfaradic Impedimetric Sensing: Trastuzumab Detection Employing a Peptide Immunosensor

A label-free and reagent-free peptide mimotope capacitive biosensor has been developed for cancer drug (trastuzumab) quantification based on nonfaradic readout. The low sensitivity issue of capacitive biosensors was overcome with two innovations: peptide mimotope mixed self-assembled monolayer (SAM) biointerface and dilution of the analysis buffer. Signal amplification was achieved through dilution of phosphate-buffered saline (PBS) to tune C_dl to dominate the overall capacitance change upon target binding, which contribution is often negligible without dilution. After 1000× dilution, the limit of detection was lowered 500-fold (0.22 μg/mL) and the sensitivity was increased 20-fold [0.04192 (μg/mL)^-1] in comparison with undiluted PBS. The proposed signal amplification strategy is more straightforward and practical compared to biorecognition element engineering and other strategies. The proposed method was further applied to planar electrodes for optimizing sensing response time to less than 1 min.

Capacitive Biosensors and Molecularly Imprinted Electrodes

Capacitive biosensors belong to the group of affinity biosensors that operate by registering direct binding between the sensor surface and the target molecule. This type of biosensors measures the changes in dielectric properties and/or thickness of the dielectric layer at the electrolyte/electrode interface. Capacitive biosensors have so far been successfully used for detection of proteins, nucleotides, heavy metals, saccharides, small organic molecules and microbial cells. In recent years, the microcontact imprinting method has been used to create very sensitive and selective biorecognition cavities on surfaces of capacitive electrodes. This chapter summarizes the principle and different applications of capacitive biosensors with an emphasis on microcontact imprinting method with its recent capacitive biosensor applications.

CMOS Electrochemical Instrumentation for Biosensor Microsystems: A Review

Modern biosensors play a critical role in healthcare and have a quickly growing commercial market. Compared to traditional optical-based sensing, electrochemical biosensors are attractive due to superior performance in response time, cost, complexity and potential for miniaturization. To address the shortcomings of traditional benchtop electrochemical instruments, in recent years, many complementary metal oxide semiconductor (CMOS) instrumentation circuits have been reported for electrochemical biosensors. This paper provides a review and analysis of CMOS electrochemical instrumentation circuits. First, important concepts in electrochemical sensing are presented from an instrumentation point of view. Then, electrochemical instrumentation circuits are organized into functional classes, and reported CMOS circuits are reviewed and analyzed to illuminate design options and performance tradeoffs. Finally, recent trends and challenges toward on-CMOS sensor integration that could enable highly miniaturized electrochemical biosensor microsystems are discussed. The information in the paper can guide next generation electrochemical sensor design.

Conjugation of Bovine Serum Albumin With ZnO Nanosphere-A Novel Approach for Ultra-Low Level Mercury Ion Detection

Solution-processed bovine serum albumin conjugated with ZnO nanosphere (BCZ) have been synthesized for ultra-low level mercury ion detection. Simple drop casting technique was adopted to fabricate such a mercury ion (Hg²⁺) detection scheme. Morphological and optical characterization of the BCZ was performed by Transmission Electron Microscopy (TEM), UV-Vis and Fluorescence spectroscopic technique prior to device fabrication. The working principle of the BCZ device for Hg²⁺ detection depends upon the variation of conductance with various concentration of Hg²⁺. An extensive study was carried out to investigate the effect of Hg²⁺ upon transport properties of BCZ. The ultra-low level of Hg²⁺ sensing was performed using this electrical detection technique. More importantly, this proposed BCZ based detection technique is found to be simple, inexpensive and very fast in responding (response time  ∼ 2.5 s) to heavy metal ion with a limit of detection (LOD) 0.03 fg/ml (S/ [Formula: see text]3).

Enhanced detection of quantum dots labeled protein by simultaneous bismuth electrodeposition into microfluidic channel

In this study, we propose an electrochemical immunoassay into a disposable microfluidic platform, using quantum dots (QDs) as labels and their enhanced detection using bismuth as an alternative to mercury electrodes. CdSe@ZnS QDs were used to tag human IgG as a model protein and detected through highly sensitive stripping voltammetry of the dissolved metallic component (cadmium in our case). The modification of the screen printed carbon electrodes (SPCEs) was done by a simple electrodeposition of bismuth that was previously mixed with the sample containing QDs. A magneto-immunosandwich assay was performed using a micromixer. A magnet placed at its outlet in order to capture the magnetic beads used as solid support for the immunoassay. SPCEs were integrated at the end of the channel as detector. Different parameters such as bismuth concentration, flow rate, and incubation times, were optimized. The LOD for HIgG in presence of bismuth was 3.5 ng/mL with a RSD of 13.2%. This LOD was about 3.3-fold lower than the one obtained without bismuth. Furthermore, the sensitivity of the system was increased 100-fold respect to experiments carried out with classical screen-printed electrodes, both in presence of bismuth.

High-throughput impedance spectroscopy biosensor array chip

Impedance spectroscopy is a powerful tool for characterizing materials that exhibit a frequency dependent behaviour to an applied electric field. This paper introduces a fully integrated multi-channel impedance extraction circuit that can both generate AC stimulus signals over a broad frequency range and also measure and digitize the real and imaginary components of the impedance response. The circuit was fabricated in a 0.5 μm complementary metal-oxide semiconductor. Tailored for cellular membrane interface characterization, the signal generator produces sinusoidal waves from 10 mHz to 10 kHz. To suit a variety of applications, the impedance extraction circuit provides a programmable current measurement range from 100 pA to 100 nA with a measured resolution of approximately 100 fA. Occupying only 0.045 mm(2) per measurement channel, the circuit is compact enough to include nearly 200 channels in a 3×3 mm(2) die area.

Development of a real-time capacitive biosensor for cyclic cyanotoxic peptides based on Adda-specific antibodies

The harmful effects of cyanotoxins in surface waters have led to increasing demands for accurate early warning methods. This study proposes a capacitive immunosensor for broad-spectrum detection of the group of toxic cyclic peptides called microcystins (∼80 congeners) at very low concentration levels. The novel analytical platform offers significant advances compared to the existing methods. Monoclonal antibodies (mAbs, clone AD4G2) that recognize a common element of microcystins were used to construct the biosensing layer. Initially, a stable insulating anchor layer for the mAbs was made by electropolymerization of tyramine onto a gold electrode surface, with subsequent incorporation of gold nanoparticles (AuNPs) on the glutaraldehyde (5%) activated polytyramine surface. The biosensor responded linearly to microcystin concentrations from 1×10(-13)M to 1×10(-10)M MC-LR standard with a limit of detection of 2.1×10(-14)M. The stability of the biosensor was evaluated by repeated measurements of the antigen and by determining the capacitance change relative to the original response, which decreased below 90% after the 30th cycle.

Detection of molecular binding via charge-induced mechanical response of optical fibers

We report a charge sensitive optical detection technique for label-free study of molecular interactions. Traditional label-free optical detection techniques largely rely on the detection of the mass of a molecule, which are insensitive to small molecules. In contrast, the present technique detects the charge of a molecule, where the signal does not diminish with the size of the molecule, thus capable for studying small molecules. In addition, the technique is compatible with the standard microplate platform, making it suitable for high-throughput screening of drug candidates. Using the technique, we have detected 0.2 nM anti-BSA and 15 μM anti-cancer drug (imatinib) with an enzyme modified surface. The achieved effective charge detection limit is ~0.25 electron charge/μm², corresponding to ~0.3 fg/mm² for imatinib, which is orders of magnitude better than traditional label-free optical detection methods.

Colorimetric sensor array based on gold nanoparticles and amino acids for identification of toxic metal ions in water

A facile colorimetric sensor array for detection of multiple toxic heavy metal ions (Hg(2+), Cd(2+), Fe(3+), Pb(2+), Al(3+), Cu(2+), and Cr(3+)) in water is demonstrated using 11-mercaptoundecanoic acid (MUA)-capped gold nanoparticles (AuNPs) and five amino acids (lysine, cysteine, histidine, tyrosine, and arginine). The presence of amino acids (which have functional groups that can form complexes with metal ions and MUA) regulates the aggregation of MUA-capped particles; it can either enhance or diminish the particle aggregation. The combinatorial colorimetric response of all channels of the sensor array (i.e., color change in each of AuNP and amino acid couples) enables naked-eye discrimination of all of the metal ions tested in this study with excellent selectivity.

A whole-cell biosensor for the detection of gold

Geochemical exploration for gold (Au) is becoming increasingly important to the mining industry. Current processes for Au analyses require sampling materials to be taken from often remote localities. Samples are then transported to a laboratory equipped with suitable analytical facilities, such as Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) or Instrumental Neutron Activation Analysis (INAA). Determining the concentration of Au in samples may take several weeks, leading to long delays in exploration campaigns. Hence, a method for the on-site analysis of Au, such as a biosensor, will greatly benefit the exploration industry. The golTSB genes from Salmonella enterica serovar typhimurium are selectively induced by Au(I/III)-complexes. In the present study, the golTSB operon with a reporter gene, lacZ, was introduced into Escherichia coli. The induction of golTSB::lacZ with Au(I/III)-complexes was tested using a colorimetric β-galactosidase and an electrochemical assay. Measurements of the β-galactosidase activity for concentrations of both Au(I)- and Au(III)-complexes ranging from 0.1 to 5 µM (equivalent to 20 to 1000 ng g(-1) or parts-per-billion (ppb)) were accurately quantified. When testing the ability of the biosensor to detect Au(I/III)-complexes(aq) in the presence of other metal ions (Ag(I), Cu(II), Fe(III), Ni(II), Co(II), Zn, As(III), Pb(II), Sb(III) or Bi(III)), cross-reactivity was observed, i.e. the amount of Au measured was either under- or over-estimated. To assess if the biosensor would work with natural samples, soils with different physiochemical properties were spiked with Au-complexes. Subsequently, a selective extraction using 1 M thiosulfate was applied to extract the Au. The results showed that Au could be measured in these extracts with the same accuracy as ICP-MS (P<0.05). This demonstrates that by combining selective extraction with the biosensor system the concentration of Au can be accurately measured, down to a quantification limit of 20 ppb (0.1 µM) and a detection limit of 2 ppb (0.01 µM).