Biosensor for acrylamide based on an ion-selective electrode using whole cells ofPseudomonas aeruginosacontaining amidase activity

An Extremely Sensitive Ultra-High Throughput Growth Selection Assay for the Identification of Amidase Activity

In the last decades, biocatalysis has offered new perspectives for the synthesis of (chiral) amines, which are essential building blocks for pharmaceuticals, fine and bulk chemicals. In this regard, amidases have been employed due to their broad substrate scope and their independence from expensive cofactors. To expand the repertoire of amidases, tools for their rapid identification and characterization are greatly demanded. In this work an ultra-high throughput growth selection assay based on the production of the folate precursor p-aminobenzoic acid (PABA) is introduced to identify amidase activity. PABA-derived amides structurally mimic the broad class of commonly used chromogenic substrates derived from p-nitroaniline. This suggests that the assay should be broadly applicable for the identification of amidases. Unlike conventional growth selection assays that rely on substrates as nitrogen or carbon source, our approach requires PABA in sub-nanomolar concentrations, making it exceptionally sensitive and ideal for engineering campaigns that aim at enhancing amidase activities from minimally active starting points, for example. The presented assay offers flexibility in the adjustment of sensitivity to suit project-specific needs using different expression systems and fine-tuning with the antimetabolite sulfathiazole. Application of this PABA-based assay facilitates the screening of millions of enzyme variants on a single agar plate within two days, without the need for laborious sample preparation or expensive instruments, with transformation efficiency being the only limiting factor. KEY POINTS: • Ultra-high throughput assay (tens of millions on one agar plate) for amidase screening • High sensitivity by coupling selection to folate instead of carbon or nitrogen source • Highly adjustable in terms of sensitivity and expression of the engineering target.

Advancements in Chemical and Biosensors for Point-of-Care Detection of Acrylamide

Acrylamide (AA), an odorless and colorless organic small-molecule compound found generally in thermally processed foods, possesses potential carcinogenic, neurotoxic, reproductive, and developmental toxicity. Compared with conventional methods for AA detection, bio/chemical sensors have attracted much interest in recent years owing to their reliability, sensitivity, selectivity, convenience, and low cost. This paper provides a comprehensive review of bio/chemical sensors utilized for the detection of AA over the past decade. Specifically, the content is concluded and systematically organized from the perspective of the sensing mechanism, state of selectivity, linear range, detection limits, and robustness. Subsequently, an analysis of the strengths and limitations of diverse analytical technologies ensues, contributing to a thorough discussion about the potential developments in point-of-care (POC) for AA detection in thermally processed foods at the conclusion of this review.

A Novel Fluorescent DNA Sensor for Acrylamide Detection in Food Samples Based on Single-Stranded DNA and GelRed

The presence of acylamide (AA) in large group of food products and its health hazards have been confirmed by scientists. In this study, a simple and innovative biosensor for AA determination was designed based on single-stranded DNA (ssDNA) with partial guanine and GelRed. The idea of this biosensor is based on the formation of AA-ssDNA adduct through the strong binding interaction between AA and guanine base of ssDNA, which subsequently inhibits the interaction of ssDNA and GelRed, leading to a weak fluorescence intensity. The binding interaction between AA and ssDNA was confirmed by UV-Vis absorption spectrometry and fluorescence intensity. Under optimum conditions, the designed biosensor exhibited excellent linear response in range of 0.01-95 mM, moreover it showed high selectivity toward AA. The limit of detection was 0.003 mM. This biosensor was successfully applied for the determination of AA in water extract of potato fries and coffee in the range of 0.05-100 mM with LOD of 0.01 mM and 0.05-95 mM with LOD of 0.004 mM, respectively.

Novel biodegradation pathway of insecticide flonicamid mediated by an amidase and its unusual substrate spectrum

The insecticide flonicamid (FLO) and its main degradation intermediate 4-trifluoromethylnicotinamide (TFNA-AM) are hazardous to the environment and animals. Microbial transformation of FLO has been well studied, but no study has yet reported on TFNA-AM degradation by a microorganism. Here, Pseudomonas stutzeri CGMCC 22915 effectively degraded TFNA-AM to 5-trifluoromethylnicotinic acid (TFNA). P. stutzeri CGMCC 22915 degraded 60.0% of TFNA-AM (1154.44 μmol/L) within 6 h with a half-life of just 4.5 h. Moreover, P. stutzeri CGMCC 22915 significantly promoted TFNA-AM decomposition in surface water. The reaction was catalyzed by an amidase, PsAmiA. PsAmiA is encoded in a novel nitrile-converting enzyme gene cluster. The enzyme shared only 20-44% identities with previously characterized signature amidases. PsAmiA was successfully expressed in Escherichia coli and its enzymatic properties were investigated using TFNA-AM as the substrate. PsAmiA was more active toward amides without hydrophilic groups, and did not hydrolyze another amide metabolite of FLO, N-(4-trifluoromethylnicotinoyl)glycinamide (TFNG-AM), which is structurally very similar to TFNA-AM. Molecular docking of PsAmiA and TFNA-AM indicated that hydrophobic residues Leu148, Ala150, Ala195, Ile225, Trp341, Leu460, and Ile463 may affect its substrate spectrum. This study provides new insights of the environmental fate of FLO at the molecular level and the structure-function relationships of amidases.

Nanomaterials Enabled and Bio/Chemical Analytical Sensors for Acrylamide Detection in Thermally Processed Foods: Advances and Outlook

Acrylamide, a food processing contaminant with demonstrated genotoxicity, carcinogenicity, and reproductive toxicity, is largely present in numerous prominent and commonly consumed food products that are produced by thermal processing methods. Food regulatory bodies such as the U.S. Food and Drug Administration (U.S. FDA) and European Union Commission regulations have disseminated various acrylamide mitigation strategies in food processing practices. Hence, in the wake of such food and public health safety efforts, there is a rising demand for economic, rapid, and portable detection and quantification methods for these contaminants. Since conventional quantification techniques like liquid chromatography-mass spectrometry (LC-MS) and gas chromatography-mass spectrometry (GC-MS) methods are expensive and have many drawbacks, sensing platforms with various transduction systems have become an efficient alternative tool for quantifying various target molecules in a wide variety of food samples. Therefore, this present review discusses in detail the state of robust, nanomaterials-based and other bio/chemical sensor fabrication techniques, the sensing mechanism, and the selective qualitative and quantitative measurement of acrylamide in various food materials. The discussed sensors use analytical measurements ranging from diverse and disparate optical, electrochemical, as well as piezoelectric methods. Further, discussions about challenges and also the potential development of the lab-on-chip applications for acrylamide detection and quantification are entailed at the end of this review.

Poly(methylene blue)-Based Electrochemical Platform for Label-Free Sensing of Acrylamide

The present work reports the electrochemical sensing of acrylamide (AM) using a poly(methylene blue)-modified glassy carbon electrode (PMB/GCE) where PMB functions as an electrochemical reporter. PMB was prepared by electrochemical polymerization of methylene blue. Electrochemical sensing of AM was facilitated by the interaction between AM and PMB. Further the interaction between AM and PMB was investigated using ultraviolet-visible (UV-vis) spectroscopy and Raman analysis. The surface morphology was confirmed by atomic force microscopy (AFM) and field emission scanning electron microscopy (FESEM) analyses. PMB/GCE was further characterized by X-ray photoelectron spectroscopy (XPS), and the electrochemical performance was assessed using cyclic voltammetry and differential pulse voltammetry. Cyclic voltammetry analysis showed a decrease in current at the redox center of PMB upon addition of AM. The association constant and binding number of AM with PMB/GCE were calculated using differential pulse voltammetry and found to be 8.9 × 10⁶ M^-1 and 0.64 (∼1), respectively. The results indicated a strong interaction of AM on the PMB/GCE surface. Further, chronocoulometry analysis of PMB/GCE in the presence of AM showed a decrease in charge due to the interaction of AM with PMB. Under optimized conditions, PMB/GCE exhibited a decrease in current proportional to the concentration of AM in the range of 0.025-16 μM with sensitivity and detection limit 0.252 μA nM^-1 and 0.13 nM, respectively. Real sample analysis was carried out by the standard addition method using the solution extracted from potato chips.

Amidase as a versatile tool in amide-bond cleavage: From molecular features to biotechnological applications

Amidases (EC 3. 5. 1. X) are versatile biocatalysts for synthesis of chiral carboxylic acids, α-amino acids and amides due to their hydrolytic and acyl transfer activity towards the C-N linkages. They have been extensively exploited and studied during the past years for their high specific activity and excellent enantioselectivity involved in various biotechnological applications in pharmaceutical and agrochemical industries. Additionally, they have attracted considerable attentions in biodegradation and bioremediation owing to environmental pressures. Motivated by industrial demands, crystallographic investigations and catalytic mechanisms of amidases based on structural biology have witnessed a dramatic promotion in the last two decades. The protein structures showed that different types of amidases have their typical stuctural elements, such as the conserved AS domains in signature amidases and the typical architecture of metal-associated active sites in acetamidase/formamidase family amidases. This review provides an overview of recent research advances in various amidases, with a focus on their structural basis of phylogenetics, substrate specificities and catalytic mechanisms as well as their biotechnological applications. As more crystal structures of amidases are determined, the structure/function relationships of these enzymes will also be further elucidated, which will facilitate molecular engineering and design of amidases to meet industrial requirements.

Development of a flow injection analytical system for short chain amide determination based on a tubular bioreactor and an ammonium sensor

Pseudomonas aeruginosa (P. aeruginosa) possesses intracellular amidase activity, which catalyses the hydrolysis of short aliphatic amides producing NH4+, and has already been used along with an ammonium ion selective electrode for amide quantification. However, the incorporation of a biological membrane turned to be a challenging process and either the final arrangement was prone to amidase losses or the recovery of the sensor coating after the interaction took too long. In this article a flow injection system with an ammonium acoustic wave sensor is proposed, and after testing several different arrangements for the biological element, the ultimate choice consisted of the immobilization of a P. aeruginosa cell-free extract in the inner wall of a tubular glass reactor, which resulted in a reliable analytical system. Response times less than one minute and complete recovery in less than two minutes assured conveniently fast analysis. The analytical system, as long as the column was properly stored in HEPES buffer containing 2 mM β-mercaptoethanol and 1 mM benzamidine and refrigerated when not in use, could be used at least for 20 working days, along a period of one month, maintaining the initial sensitivity.

An electrochemical biosensor based on hemoglobin-oligonucleotides-modified electrode for detection of acrylamide in potato fries

Acrylamide a neurotoxin and strong carcinogen, is found in various thermally processed foods. In this study, an electrochemical sensor for detection of acrylamide using double stranded DNA (dsDNA)/Hemoglobin (Hb)-modified screen printed gold electrode (SPGE) was designed. The immobilization of ssDNA1-SH on the surface of SPGE was confirmed by cyclic voltammetry, and the interaction between ssDNA2-NH₂ and Hb with the ratio 1:1 was characterized by agarose gel. The excellent response of the designed biosensor towards acrylamide due to acrylamide and Hb adducts and change of reduction/oxidation process of Hb-Fe(III)/Hb-Fe(II) was determined by square wave voltammetry (SWV). The biosensor showed the optimum response at pH 8.0. The linear working range for acrylamide was from 2.0 × 10^-6 to 5.0 × 10^-2 M with a detection limit of 1.58 × 10^-7 M. The biosensor was suitable for direct determination of acrylamide in water extracted of potato fries and displayed good reproductivity and high stability.

Biosensors in food processing

Optical based sensing systems that measure luminescence, fluorescence, reflectance and absorbance, etc., are some of the areas of applications of optical immunosensors. Immunological methods rely on specific binding of an antibody (monoclonal, polyclonal or engineered) to an antigen. Detection of specific microorganisms and microbial toxins requires immobilization of specific antibodies onto a given transducer that can produce signal upon attachment of typical microbe/microbial toxins. Inherent features of immunosensors such as specificity, sensitivity, speed, ease and on-site analysis can be made use for various applications. Safety of food and environment has been a major concern of food technologists and health scientists in recent years. There exists a strong need for rapid and sensitive detection of different components of foods and beverages along with the food borne and water borne pathogens, toxins and pesticide residues with high specificity. Biosensors present attractive, efficient alternative techniques by providing quick and reliable performances. There is a very good potential for application of biosensors for monitoring food quality and safety in food and bioprocessing industries in India.

New trends in quantification of acrylamide in food products

Methods applied in acrylamide quantification in foods have been reviewed in this paper. Novel analytical techniques like capillary electrophoresis (CE), immunoenzymatic test (ELISA) and electrochemical biosensors, which can replace traditional methods like high performance liquid chromatography (HPLC) and gas chromatography (GC) were presented. Short time of analysis and high resolution power of electrophoretic techniques caused that they became routinely used in food analysis apart from high performance liquid chromatography and gas chromatography. Application of modern chromatography methods like ultra performance liquid chromatography (UPLC) in acrylamide quantification considerably shortened the time of analysis and decreased the consumption of indispensable reagents. The most promising approaches to acrylamide quantification in foods are electrochemical biosensors and immunoenzymatic tests. In contrast to chromatography and electrophoretic methods they require neither expensive equipment nor time consuming sample preparation and allow for fast screening of numerous samples without the usage of sophisticated apparatuses. Because of many advantages such as miniaturization, rapid and simple analysis, and high sensitivity and selectivity, biosensors are thought to replace conventional methods of acrylamide quantification in food.