Whole-cell Biosensors Research Articles

Transcription factor-based biosensors for detection of naturally occurring phenolic acids

Phenolic acids including hydroxybenzoic and hydroxycinnamic acids are secondary plant and fungal metabolites involved in many physiological processes offering health and dietary benefits. They are often utilised as precursors for production of value-added compounds. The limited availability of synthetic biology tools, such as whole-cell biosensors suitable for monitoring the dynamics of phenolic acids intracellularly and extracellularly, hinders the capabilities to develop high-throughput screens to study their metabolism and forward engineering. Here, by applying a multi-genome approach, we have identified phenolic acid-inducible gene expression systems composed of transcription factor-inducible promoter pairs responding to eleven different phenolic acids. Subsequently, they were used for the development of whole-cell biosensors based on model bacterial hosts, such as Escherichia coli, Cupriavidus necator and Pseudomonas putida. The dynamics and range of the biosensors were evaluated by establishing their response and sensitivity landscapes. The specificity and previously uncharacterised interactions between transcription factor and its effector(s) were identified by a screen of twenty major phenolic acids. To exemplify applicability, we utilise a protocatechuic acid-biosensor to identify enzymes with enhanced activity for conversion of p-hydroxybenzoate to protocatechuate. Transcription factor-based biosensors developed in this study will advance the analytics of phenolic acids and expedite research into their metabolism.

Directed evolution of TetR for constructing sensitive and broad-spectrum tetracycline antibiotics whole-cell biosensor

Antibiotic abuse is the main reason for the drug resistance of pathogenic bacteria, posing a potential health risk. Antibiotic surveillance is critical for preventing antibiotic contamination. This study aimed to develop a sensitive and broad-spectrum whole-cell biosensor for tetracycline antibiotics (TCs) detection. Wild-type TCs-responsive biosensor was constructed by introducing a tetracycline operon into a sfGFP reporter plasmid. Using error-prone PCR, mutation libraries containing approximately 107 variants of the tetracycline repressor (TetR) gene were generated. The tigecycline-senstive mutants were isolated using high-throughput flow cytometric sorting. After 2 rounds of directed evolution, a mutant epS2–22 of TerR was isolated and assembled as a TCs biosensor. The epS2–22 biosensor was more sensitive and broad-spectrum than the wild-type biosensors. The detection limits of the epS2–22 biosensor for seven TCs were 4- to 62-fold lower than the wild-type biosensor (no response to tigecycline). Meanwhile, the epS2–22 biosensor had a shorter detection time and a stronger signal output than the wild type. In addition, the evolved epS2–22 biosensor showed excellent performance in detecting low traces of TCs in environmental water. These results suggest that directed evolution is a powerful tool for developing high-performance whole-cell biosensors, and the evolved epS2–22 biosensors have the potential for wider applications in real-world TCs detection.

Mini Review on the Potential of Algal Biosensors in Wastewater Monitoring

Abstract:: For biomass production and bioremediation, Algae have been extensively exploited for biosensing in wastewater monitoring. Their advantages include the coupling of suitable bioreceptor for monitoring photosynthesis oxygen, their potential to be integrated into dual transduction miniaturized devices and detect the effect due to pollutants present in water with continuous monitoring of the environment. Microalgae are photosynthetic microorganisms that are very sensitive and reactive toward any change in the environment. And also able to detect any trace amount of pollutants. The performance of algal biosensors towards pollutants represents a good alternative to other developing sensors. In the algal biosensor, the algal cell is entrapped in galling material (Alginate, Carrageenan) and immobilized cells for stabilization with ions (Ca2+, K+). Genetically modified biosensor overcomes the limitation of natural biosensor. Whole-cell biosensors are highly sensitive to herbicides in wastewater, and many other bioreceptor of algal cells those sensitive to different types of pollutants. The present algal sensor is much smaller, valid support in smart agriculture, environmentally friendly and less expensive, the easily accessible.

Development of a Novel ATP Bioluminescence Assay Based on Engineered Probiotic Saccharomyces boulardii Expressing Firefly Luciferase.

Quantitative analysis of adenosine triphosphate (ATP) has been widely used as a diagnostic tool in the food and medical industries. Particularly, the pathogenesis of a few diseases including inflammatory bowel disease (IBD) is closely related to high ATP concentrations. A bioluminescent D-luciferin/luciferase system, which includes a luciferase (FLuc) from the firefly Photinus pyralis as a key component, is the most commonly used method for the detection and quantification of ATP. Here, instead of isolating FLuc produced in recombinant Escherichia coli, we aimed to develop a whole-cell biocatalyst system that does not require extraction and purification of FLuc. To this end, the gene coding for FLuc was introduced into the genome of probiotic Saccharomyces boulardii using the CRISPR/Cas9-based genome editing system. The linear relationship (r2 = 0.9561) between ATP levels and bioluminescence generated from the engineered S. boulardii expressing FLuc was observed in vitro. To explore the feasibility of using the engineered S. boulardii expressing FLuc as a whole-cell biosensor to detect inflammation biomarker (i.e., ATP) in the gut, a colitis mouse model was established using dextran sodium sulfate as a colitogenic compound. Our findings demonstrated that the whole-cell biosensor can detect elevated ATP levels during gut inflammation in mice. Therefore, the simple and powerful method developed herein could be applied for non-invasive IBD diagnosis.

Pb(II)-inducible proviolacein biosynthesis enables a dual-color biosensor toward environmental lead.

With the rapid development of synthetic biology, various whole-cell biosensors have been designed as valuable biological devices for the selective and sensitive detection of toxic heavy metals in environmental water. However, most proposed biosensors are based on fluorescent and bioluminescent signals invisible to the naked eye. The development of visible pigment-based biosensors can address this issue. The pbr operon from Klebsiella pneumoniae is selectively induced by bioavailable Pb(II). In the present study, the proviolacein biosynthetic gene cluster was transcriptionally fused to the pbr Pb(II) responsive element and introduced into Escherichia coli. The resultant biosensor responded to Pb(II) in a time- and dose-dependent manner. After a 5-h incubation with Pb(II), the brown pigment was produced, which could be extracted into n-butanol. Extra hydrogen peroxide treatment during n-butanol extract resulted in the generation of a stable green pigment. An increased brown signal was observed upon exposure to lead concentrations above 2.93 nM, and a linear regression was fitted from 2.93 to 3,000 nM. Extra oxidation significantly decreased the difference between parallel groups. The green signal responded to as low as 0.183 nM Pb(II), and a non-linear regression was fitted in a wide concentration range from 0.183 to 3,000 nM. The specific response toward Pb(II) was not interfered with by various metals except for Cd(II) and Hg(II). The PV-based biosensor was validated in monitoring bioaccessible Pb(II) spiked into environmental water. The complex matrices did not influence the regression relationship between spiked Pb(II) and the dual-color signals. Direct reading with the naked eye and colorimetric quantification enable the PV-based biosensor to be a dual-color and low-cost bioindicator for pollutant heavy metal.

Development of a whole-cell biosensor for detecting organophosphorus pesticide methyl parathion in the farmland soil

The evaluation of the bioavailability of pollutants in soil is crucial to accurately assess the pollution risk, and whole-cell biosensor is one of the important tools for such evaluation. This study aimed to develop a novel whole-cell biosensor for the detection of methyl parathion in soil using. First, a whole-cell biosensor was constructed by the screened methyl parathion hydrolase mpd gene, the existing specific induction element pobR, and the pUC19 plasmid skeleton. Then, the detection method of methyl parathion in soil extracts was established using 96-well microtiter plate as carrier and five whole-cell biosensors as indicator. The method was applied in the detection of methyl parathion in tested and field soil extracts. Taking E. coli DH5α/pMP-AmilCP with the best detection performance as an example, this biosensor had a detection limit of 6.21-6.66 µg/L and a linear range of 10-10 000 µg/L for methyl parathion in four soil extracts. E. coli DH5α/pMP-RFP and E. coli DH5α/pMP-AmilCP methods have good detection performance for the analysis of methyl parathion in soil extract samples. This biosensor method can help to quickly assess the bioavailability of methyl parathion in soil, and thus help to understand the risk of soil pollution caused by organophosphorus pesticide methyl parathion.

Development of Nanobody-Displayed Whole-Cell Biosensors for the Colorimetric Detection of SARS-CoV-2.

The accurate and effective detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is essential to preventing the spread of infectious diseases and ensuring human health. Herein, a nanobody-displayed whole-cell biosensor was developed for colorimetric detection of SARS-CoV-2 spike proteins. Serving as bioreceptors, yeast surfaces were genetically engineered to display SARS-CoV-2 binding of llama-derived single-domain antibodies (nanobodies) with high capture efficiency, facilitating the concentration and purification of SARS-CoV-2. Gold nanoparticles (AuNPs) employed as signal transductions were functionalized with horseradish peroxidase (HRP) and anti-SARS monoclonal antibodies to enhance the detection sensitivity. In the presence of SARS-CoV-2 spike proteins, the sandwiched binding will be formed by linking engineered yeast, SARS-CoV-2 spike proteins, and reporter AuNPs. The colorimetric signal was generated by the enzymatic reaction of HRP and its corresponding colorimetric substrate/chromogen system. At the optimal conditions, the developed whole-cell biosensor enables the sensitive detection of SARS-CoV-2 spike proteins in a linear range from 0.01 to 1 μg/mL with a limit of detection (LOD) of 0.037 μg/mL (about 4 × 108 virion particles/mL). Furthermore, the whole-cell biosensor was demonstrated to detect the spike protein of different SARS-CoV-2 variants in human serum, providing new possibilities for the detection of future SARS-CoV-2 variants.

Natural Microbial Reactor-Based Sensing Platform for Highly Sensitive Detection of Inorganic Arsenic in Rice Grains.

Rice is a major dietary source of inorganic arsenic (iAs), a highly toxic arsenical that accumulates in rice and poses health risks to rice-based populations. However, the availability of detection methods for iAs in rice grains is limited. In this study, we developed a novel approach utilizing a natural bacterial biosensor, Escherichia coli AW3110 (pBB-ArarsR-mCherry), in conjunction with amylase hydrolysis for efficient extraction, enabling high-throughput and quantitative detection of iAs in rice grains. The biosensor exhibits high specificity for arsenic and distinguishes between arsenite [As(III)] and arsenate [As(V)] by modulating the concentration of PO43- in the detection system. We determined the iAs concentrations in 19 rice grain samples with varying total As concentrations and compared our method with the standard technique of microwave digestion coupled with HPLC-ICP-MS. Both methods exhibited comparable results, without no significant bias in the concentrations of As(III) and As(V). The whole-cell biosensor demonstrated excellent reproducibility and a high signal-to-noise ratio, achieving a limit of detection of 16 μg kg-1 [As(III)] and 29 μg kg-1 [As(V)]. These values are considerably lower than the maximum allowable level (100 μg kg-1) for infant rice supplements established by the European Union. Our straightforward sensing strategy presents a promising tool for detecting iAs in other food samples.

A portable, encapsulated microbial whole-cell biosensing system for the detection of bioavailable copper (II) in soil

A portable, field deployable whole-cell biosensor was developed that can withstand the complex matrices of soil and requires minimal to no sample preparation to monitor bioavailable concentrations of the essential micronutrient copper (II). Conventional measurement of micronutrients is often complex, laboratory-based, and not suitable for monitoring their bioavailable concentration. To address this need, we developed a fluorescence based microbial whole-cell biosensing (MWCB) system encoding for a Cu2+-responsive protein capable of generating a signal upon binding to Cu2+. The sensing-reporting protein was designed by performing circular permutation on the green fluorescent protein (GFP) followed by insertion of a Cu2+ binding motif into the structure of GFP. The design included insertion of several binding motifs and creating plasmids that encoded the corresponding sensing proteins. The signal generated by the sensing-reporting protein is directly proportional to the concentration of Cu2+ in the sample. Evaluation of the resulting biosensing systems carrying these plasmids was performed prior to selection of the optimal fluorescence emitting Cu2+-binding protein. The resulting optimized biosensing system was encapsulated in polyacrylate-alginate beads and embedded in soil for detection of the analyte. Once exposed to the soil, the beads were interrogated to measure the fluorescence signal emitted by the sensing-reporting protein using a portable imaging device. The biosensor was optimized for detection of Cu2+ in terms of selectivity, sensitivity, matrix effects, detection limits, and reproducibility in both liquid and soil matrices. The limit of detection (LoD) of the optimized encapsulated biosensor was calculated as 0.27 mg/L and 1.26 mg/kg of Cu2+ for Cu2+ in solution and soil, respectively. Validation of the portable imaging tools as a potential biosensing device in the field was performed.

Harnessing split fluorescent proteins in modular protein logic for advanced whole-cell detection

Whole-cell biosensors have demonstrated promising capabilities in detecting target molecules. However, their limited selectivity and precision can be attributed to the broad substrate tolerance of natural proteins. In this study, we aim to enhance the performance of whole-cell biosensors by incorporating of logic AND gates. Specifically, we utilize the HrpR/S system, a widely employed hetero-regulation module from Pseudomonas syringae in synthetic biology, to construct an orthogonal AND gate in Escherichia coli. To accomplish this, we compare the HrpR/S system with self-associating split fluorescent proteins using the Spy Tag/Spy Catcher system. Our objective is to selectively activate a reporter gene in the presence of both IPTG and Hg(II) ions. Through systematic genetic engineering and evaluation of various biological parts under diverse working conditions, our research demonstrates the utility of self-associating split fluorescent proteins in developing high-performance whole-cell biosensors. This approach offers advantages such as engineering simplicity, reduced basal activity, and improved selectivity. Furthermore, the comparison with the HrpR/S system serves as a valuable control model, providing insights into the relative advantages and limitations of each approach. These findings present a systematic and adaptable strategy to overcome the substrate tolerance challenge faced by whole-cell biosensors.

Design of a Whole-Cell Biosensor Based on Bacillus subtilis Spores and the Green Fluorescent Protein To Monitor Arsenic.

A green fluorescent protein (GFP)-based whole-cell biosensor (WCB-GFP) for monitoring arsenic (As) was developed in Bacillus subtilis. To this end, we designed a reporter gene fusion carrying the gfpmut3a gene under the control of the promoter/operator region of the arsenic operon (Pars::gfpmut3a) in the extrachromosomal plasmid pAD123. This construct was transformed into B. subtilis 168, and the resultant strain was used as a whole-cell biosensor (BsWCB-GFP) for the detection of As. The BsWCB-GFP was specifically activated by inorganic As(III) and As(V), but not by dimethylarsinic acid [DMA(V)], and exhibited high tolerance to the noxious effects of arsenic. Accordingly, after 12 h exposure, B. subtilis cells carrying the Pars::gfpmut3a fusion exhibited 50 and 90% lethal doses (LD50 and LD90) to As(III) of 0.89 mM and As 1.71 mM, respectively. Notably, dormant spores from the BsWCB-GFP were able to report the presence of As(III) in a concentration range from 0.1 to 1,000 μM 4 h after the onset of germination. In summary, the specificity and high sensitivity for As, as well as its ability to proliferate under concentrations of the metal that are considered toxic in water and soil, makes the B. subtilis biosensor developed here a potentially important tool for monitoring environmental samples contaminated with this pollutant. IMPORTANCE Arsenic (As) contamination of groundwater is associated with serious worldwide health risks. Detection of this pollutant at concentrations that are established as permissible for water consumption by WHO is a matter of significant interest. Here, we report the generation of a whole-cell biosensor for As detection in the Gram-positive spore former B. subtilis. This biosensor reports the presence of inorganic As, activating the expression of the green fluorescent protein (GFP) under the control of the promoter/operator of the ars operon. The biosensor can proliferate under concentrations of As(III) that are considered toxic in water and soil and detect this ion at concentrations as low as 0.1 μM. Of note, spores of the Pars-GFP biosensor exhibited the ability to detect As(III) following germination and outgrowth. Therefore, this novel tool has the potential to be directly applied to monitor As contamination in environmental samples.

Fusion proteins of organophosphorus hydrolase and pHluorin for a whole-cell biosensor for organophosphorus pesticide measurement.

Fusion proteins composed of an organophosphorus hydrolase (OPH) and pHluorin, a pH-sensitive green fluorescent protein variant, were constructed as whole-cell biosensors to measure organophosphorus pesticides. pHluorin was used to detect the pH changes because of the hydrolase of paraoxon by OPH. To examine the order of fusion of OPH and pHluorin, pHluorin-OPH and OPH-pHluorin fusion proteins were constructed. In addition, a peptide linker consisting of 15 amino acid was inserted between pHluorin and OPH to reduce steric hindrance. OPH and pHluorin activities were evaluated in cells expressing the four fusion proteins. The both activities of pHluorin-OPH and pHluorin-linker-OPH were higher than that of OPH-pHluorin and OPH-linker-pHluorin. Effects of the peptide linker on the activities were slight. Therefore, pHluorin-OPH and pHluorin-linker-OPH were found to be suitable for organophosphorus pesticide measurements. Using cells expressing pHluorin-linker-OPH, 0.5μg/mL of paraoxon could be measured.

Regulatory transcription factor (CooA)-driven carbon monoxide partial pressure sensing whole-cell biosensor

We designed and constructed a whole-cell biosensor capable of detecting the presence and quantity of carbon monoxide (CO) using the CO regulatory transcription factor. This biosensor utilizes CooA, a CO-sensing transcription regulator that activates the expression of carbon monoxide dehydrogenase (CODH), to detect the presence of CO and respond by triggering the expression of a GUS reporter protein (β-glucuronidase). The GUS reporter protein is expressed from a CO-induced CooA-binding promoter (PcooF) by CooA and enables the effective colorimetric detection of CO. An Escherichia coli strain used to validate the biosensor showed growth and GUS activity under anaerobic conditions; this study used the inert gas (Ar) to create anaerobic conditions. The pBRCO biosensor could successfully detect the presence of CO in the headspace. Moreover, the GUS-specific activity of pBRCO according to the CO strength as partial pressure followed Michaelis-Menten kinetics (R2 = 0.98). It was confirmed that the GUS-specific activity of pBRCO increased linearly up to 30.39 kPa (R2 = 0.98), and thus, a quantitative analysis of CO concentration (i.e., partial pressure) was possible.

Development of an Efficient FRET-Based Ratiometric Uranium Biosensor.

The dispersion of uranium in the environment can pose a problem for the health of humans and other living organisms. It is therefore important to monitor the bioavailable and hence toxic fraction of uranium in the environment, but no efficient measurement methods exist for this. Our study aims to fill this gap by developing a genetically encoded FRET-based ratiometric uranium biosensor. This biosensor was constructed by grafting two fluorescent proteins to both ends of calmodulin, a protein that binds four calcium ions. By modifying the metal-binding sites and the fluorescent proteins, several versions of the biosensor were generated and characterized in vitro. The best combination results in a biosensor that is affine and selective for uranium compared to metals such as calcium or other environmental compounds (sodium, magnesium, chlorine). It has a good dynamic range and should be robust to environmental conditions. In addition, its detection limit is below the uranium limit concentration in drinking water defined by the World Health Organization. This genetically encoded biosensor is a promising tool to develop a uranium whole-cell biosensor. This would make it possible to monitor the bioavailable fraction of uranium in the environment, even in calcium-rich waters.

Pandemic COVID-19 ends but soil pollution increases: Impacts and a new approach for risk assessment

For three years, a large amount of manufactured pollutants such as plastics, antibiotics and disinfectants has been released into the environment due to COVID-19. The accumulation of these pollutants in the environment has exacerbated the damage to the soil system. However, since the epidemic outbreak, the focus of researchers and public attention has consistently been on human health. It is noteworthy that studies conducted in conjunction with soil pollution and COVID-19 represent only 4 % of all COVID-19 studies. In order to enhance researchers' and the public awareness of the seriousness on the COVID-19 derived soil pollution, we propose the viewpoint that “pandemic COVID-19 ends but soil pollution increases” and recommend a whole-cell biosensor based new method to assess the environmental risk of COVID-19 derived pollutants. This approach is expected to provide a new way for environmental risk assessment of soils affected by contaminants produced from the pandemic.

A panel of visual bacterial biosensors for the rapid detection of genotoxic and oxidative damage: A proof of concept study.

The emergence of new compounds during the past decade requires a high-throughput screening method for toxicity assay. The stress-responsive whole-cell biosensor is a powerful tool to evaluate direct or indirect damages of biological macromolecules induced by toxic chemicals. In this proof-of-concept study, nine well-characterized stress-responsive promoters were first selected to assemble a set of blue indigoidine-based biosensors. The PuspA-based, PfabA-based, and PgrpE-based biosensors were eliminated due to their high background. A dose-dependent increase of visible blue signal was observed in PrecA-, PkatG-, and PuvrA-based biosensors, responsive to potent mutagens, including mitomycin and nalidixic acid, but not to genotoxic lead and cadmium. The PrecA, PkatG, and Ppgi gene promoters were further fused to a purple deoxyviolacein synthetic enzyme cluster. Although high basal production of deoxyviolacein is unavoidable, an enhanced visible purple signal in response to mitomycin and nalidixic acid was observed as dose-dependent, especially in PkatG-based biosensors. The study shows that a set of stress-responsive biosensors employing visible pigment as a reporter is pre-validating in detecting extensive DNA damage and intense oxidative stress. Unlike widely-used fluorescent and bioluminescent biosensors, the visual pigment-based biosensor can become a novel, low-cost, mini-equipment, and high-throughput colorimetric device for the toxicity assessment of chemicals. However, combining multiple improvements can further improve the biosensing performance in future studies.

Advances in Synthetic-Biology-Based Whole-Cell Biosensors: Principles, Genetic Modules, and Applications in Food Safety.

A whole-cell biosensor based on synthetic biology provides a promising new method for the on-site detection of food contaminants. The basic components of whole-cell biosensors include the sensing elements, such as transcription factors and riboswitches, and reporting elements, such as fluorescence, gas, etc. The sensing and reporting elements are coupled through gene expression regulation to form a simple gene circuit for the detection of target substances. Additionally, a more complex gene circuit can involve other functional elements or modules such as signal amplification, multiple detection, and delay reporting. With the help of synthetic biology, whole-cell biosensors are becoming more versatile and integrated, that is, integrating pre-detection sample processing, detection processes, and post-detection signal calculation and storage processes into cells. Due to the relative stability of the intracellular environment, whole-cell biosensors are highly resistant to interference without the need of complex sample preprocessing. Due to the reproduction of chassis cells, whole-cell biosensors replicate all elements automatically without the need for purification processing. Therefore, whole-cell biosensors are easy to operate and simple to produce. Based on the above advantages, whole-cell biosensors are more suitable for on-site detection than other rapid detection methods. Whole-cell biosensors have been applied in various forms such as test strips and kits, with the latest reported forms being wearable devices such as masks, hand rings, and clothing. This paper examines the composition, construction methods, and types of the fundamental components of synthetic biological whole-cell biosensors. We also introduce the prospect and development trend of whole-cell biosensors in commercial applications.

Genetically engineered bacterial strains constructed as a whole-cell biosensor for specific volatiles identification of infected potato tubers with a soft rot disease

The potato (Solanum tuberosum) is the most globally popular non-cereal crop. During postharvest storage, the potato is susceptible to various diseases. Specifically, the symptoms of tuber soft rot can be identified visibly only after irreversible damage has already been caused. The existing technologies are not optimized for the identification of hidden diseases, thus, an early and sensitive diagnostic tool is needed. An attractive early-stage technology is based on monitoring the volatile organic compounds (VOCs) as indicators of pathogen presence. In this study, genetically engineered bacterial strains were constructed as a whole-cell biosensor for specific volatiles identification of infected potato tubers with soft rot disease. Identified volatiles were chosen (i.e., 1-Octanol, 2-Phenylethyl Alcohol, and 1-Octen-3-ol) as model toxicants and used for the identification of the responsive promoters in the host cell Escherichia coli through RNA sequencing and bioinformatic analysis. Furthermore, the promoter activity was verified by a fusion to luciferase-harboring plasmid. The bioluminescent bacterial cells monitor the changes in the VOC profile, and a signal change is then generated, reflecting the infection status of the potatoes. The efficacy of the recombinant bacteria to monitor potato soft rot disease was investigated in solution, surrounding air near pure volatiles, and around potato tubers contaminated by Pectobacterium. The results demonstrated that the new strains were sensitive to the presence of these VOCs, each to a different extent and in a different environment (solution or surrounding air). All of them except oxyR could detect differences between infected and uninfected potato tubers. The preferred bioreporter to detect Pectobacterium infection in whole potato tubers is dnaK. This strain responds to all tested volatiles in the liquid and gaseous states and has shown the highest response differences as a reaction to the infection presence in the whole potato tubers. Bacterial monitoring of the volatile profile results in identifying specific signatures that will allow quick and accurate detection of the presence of pathogens in stored crops, prior to visible disease symptoms.

Electrochemical Sensing and Biosensor Based on Functional Polymers

Functional polymers has great importance in the field of electrochemical sensing and biosensors due to adaptable chemical, electrical, and structural features, functional polymers are a significant class of materials that have been extensively used to create electrochemical biosensors. Additionally, conducting polymers can be made nanostructured, functional group-grafted chemically, or combined with other functional materials, like nanoparticles, to significantly enhance the sensitivity, selectivity, stability, and reproducibility of the biosensor's response to a variety of bioanalytes. Since these biosensors offer benefits such being affordable and having a low detection limit, they are anticipated to play an increasingly important role in providing diagnostic information and monitoring therapy. Because of this, this article begins with a description of the electroanalytical techniques (amperometry, potentiometry, conductometry, impedometry, voltammetry) used in electrochemical biosensors, and then moves on to a review of recent developments in the use of conducting polymers in the identification of bioanalytes that led to the development of enzyme-based biosensors, immunosensors, DNA biosensors, and whole-cell biosensors.

Sol-Gel Immobilized Optical Microalgal Biosensor for Monitoring Cd, Cu and Zn Bioavailability in Freshwater.

While analytical measurements provide the quantitative estimation of the total amount of metals present in a sample, they do not reflect the truly bioavailable fraction of metal which reflects the adverse biological effect. Hence the development of monitoring tools for detecting bioavailable toxic metals has become a priority in environmental monitoring activities. An optical whole-cell biosensor was constructed using the microalga Scenedesmus subspicatus MM1 immobilizing in inorganic silica hydrogels using the sol-gel technique to detect bioavailable Cadmium (Cd2+), Copper (Cu2+) and Zinc (Zn+) in freshwater. Conditions for optimum biosensor performance have been established regarding effective pH range, cell density, exposure time, and storage stability. The optimum response for the biosensor was dependent on the pH of the matrix, cell concentration and exposure time were derived. The biosensor was operational for four weeks. The limit of detection for the algal biosensor was determined as 9.0 × 10-1, 9.1 × 10-1, and 8.8 × 10-1mg/L for Cd, Cu and Zn, respectively. Whole-cell cell biosensor will be highly useful since it comprises a single microalgal species able to detect the bioavailable content of Cd2+, Cu2+, and Zn2+ in freshwater.