New materials for electrochemical sensing III. Beads

Recent advances of sensing strategies for the detection of β-glucuronidase activity

β-Glucuronidase (β-GLU), a kind of hydrolase, is widely distributed in mammalian tissues, body fluids, and microbiota. Abnormal changes of β-GLU activity are often correlated with the occurrence of diseases and deterioration of water quality. Therefore, detection of β-GLU activity is of great significance in biomedicine and environmental health such as cancer diagnosis and water monitoring. However, the conventional β-GLU activity assay suffers from the limitations of low sensitivity, poor accuracy, and complex procedure. With the development of analytical chemistry, many advances have been made in the detection of β-GLU activity in recent years. The sensors for β-GLU activity detection which have the advantages of rapid and reliable detection have been attracting increased attentions. In this paper, the principles, performances, and limitations of these β-GLU sensors, including colorimetric sensing, fluorescent sensing, electrochemical sensing for the determination of β-GLU activity, have been summarized and discussed. Moreover, the challenges and research trends of β-GLU activity assay are proposed.

Fabrication of label-free and ultrasensitive electrochemical immunosensor based on molybdenum disulfide nanoparticles modified disposable ITO: An analytical platform for antibiotic detection in food samples

Here, we aimed to fabricate a label-free immunosensing platform for the first time based on molybdenum disulfide nanoparticles (nMoS₂NPs) deposited on ITO) coated glass substrate for the electrochemical detection of ampicillin (AMP). The stable and high surface area of nMoS₂NPs were made by a low-temperature one-step hydrothermal route, bestowing the carrying capacity of anti-AMP (antibody against AMP) through an amide linkage. The spectroscopic, morphological, and structural characterization of the proposed electrodes were performed using various analytical and electrochemical techniques. The differential pulse voltammetry technique was utilized to evaluate anti-AMP and AMP interaction on the electrode surface. The developed immunosensor exhibits high sensitivity, a broad detection range having a significant detection limit towards detection of AMP having excellent selectivity, acceptable stability, and reproducibility. Furthermore, the applicability of the proposed immunosensor was tested in spiked milk, water, and orange juice, and the results confirmed the consistency of the immunosensor.

Immobilization of Enzymes on Magnetic Beads Through Affinity Interactions

The development of enzyme immobilization techniques that will not affect catalytic activity and conformation is an important research task. Affinity tags that are present or added at a specific position far from the active site in the structure of the native enzyme could be used to create strong affinity bonds between the protein structure and a surface functionalized with the complementary affinity ligand. These immobilization techniques are based on affinity interactions between biotin and (strept)avidin molecules, lectins and sugars, or metal chelate and histidine tag.Recent developments involve immobilization of tagged enzymes onto magnetic nanoparticles. These supports can improve the performance of immobilized biomolecules in analytical assay because magnetic beads provide a relative large numbers of binding sites for biochemical reactions resulting in faster assay kinetics.This chapter describes immobilization procedures of tagged enzymes onto various magnetic beads.

Magnetic control of graphitic microparticles in aqueous solutions

Graphite is an inexpensive material with useful electrical, magnetic, thermal, and optical properties. It is also biocompatible and used universally as a substrate. Micrometer-sized graphitic particles in solution are therefore ideal candidates for novel lab-on-a-chip and remote manipulation applications in biomedicine, biophysics, chemistry, and condensed-matter physics. However, submerged graphite is not known to be amenable to magnetic manipulation, the optimal manipulation method for such applications. Here, we exploit the diamagnetism of graphite and demonstrate contactless magnetic positioning control of graphitic microflakes in diamagnetic aqueous solutions. We develop a theoretical model for magnetic manipulation of graphite microflakes and demonstrate experimentally magnetic transport of such particles over distances [Formula: see text] with peak velocities [Formula: see text] in inhomogeneous magnetic fields. We achieve fully biocompatible transport for lipid-coated graphite in NaCl aqueous solution, paving the way for previously undiscovered biomedical applications. Our results prove that micrometer-sized graphite can be magnetically manipulated in liquid media.

Magneto-electrical orientation of lipid-coated graphitic micro-particles in solution

We demonstrate, for the first time, confinement of the orientation of graphitic micro-flakes to a well-defined plane in solution by applying two perpendicular fields: a vertical static magnetic field and a horizontal time-varying electric field.

Biomedical Perspective of Electrochemical Nanobiosensor

Electrochemical biosensor holds great promise in the biomedical area due to its enhanced specificity, sensitivity, label-free nature and cost effectiveness for rapid point-of-care detection of diseases at bedside. In this review, we are focusing on the working principle of electrochemical biosensor and how it can be employed in detecting biomarkers of fatal diseases like cancer, AIDS, hepatitis and cardiovascular diseases. Recent advances in the development of implantable biosensors and exploration of nanomaterials in fabrication of electrodes with increasing the sensitivity of biosensor for quick and easy detection of biomolecules have been elucidated in detail. Electrochemical-based detection of heavy metal ions which cause harmful effect on human health has been discussed. Key challenges associated with the electrochemical sensor and its future perspectives are also addressed.

Realization of fluorescence color tuning for poly(p-phenylenevinylene) coated microspheres via a heterogeneous catalytic thermal elimination process

Fluorescent microspheres with clear core–shell structures and various emission colors were successfully prepared via a catalytic elimination process.

Electrochemical detection of fluoroquinolone antibiotics in milk using a magneto immunosensor

An amperometric magneto-immunosensor (AMIS) for the detection of residues of fluoroquinolone antibiotics in milk samples is described for the first time. The immunosensor presented combines magnetic beads biomodified with an antibody with a broad recognition profile of fluoroquinolones, a haptenized enzyme and a magnetic graphite–epoxy composite (m-GEC) electrode. After the immunochemical reaction with specific enzyme tracer, the antibody biomodified magnetic beads are easily captured by an electrode made of graphite-epoxy composite containing a magnet, which also acts as transducer for the electrochemical detection. In spite of the complexity of milk, the use of magnetic beads allows elimination of potential interferences caused by the matrix components; hence the AMIS could perform quantitative measurements, directly in these samples, without any additional sample cleanup or extraction step. The immunosensor is able to detect up to seven different fluoroquinolones far below the MRLs defined by the UE for milk; for example ciprofloxacin is detected directly in milk with an IC₅₀ of 0.74 μg/L and a LOD of 0.009 μg/L. This strategy offers great promise for rapid, simple, cost-effective, and on-site analysis fluoroquinolones in complex samples.

Immobilization of enzymes on magnetic beads through affinity interactions

The development of enzyme immobilization techniques that will not affect catalytic activity and conformation is an important research task. Affinity tags that are present or added at a specific position far from the active site in the structure of the native enzyme could be used to create strong affinity bonds between the protein structure and a surface functionalized with the complementary affinity ligand. These immobilization techniques are based on affinity interactions between biotin and (strept)avidin molecules, lectins and sugars, or metal chelate and histidine tag. Recent developments involve immobilization of tagged enzymes onto magnetic nanoparticles. These supports can improve the performance of immobilized biomolecules in analytical assay because magnetic beads provide a relative large numbers of binding sites for biochemical reactions resulting in faster assay kinetics. This chapter describes immobilization procedures of tagged enzymes onto various magnetic beads.

Lab-on-a-chip for ultrasensitive detection of carbofuran by enzymatic inhibition with replacement of enzyme using magnetic beads

In this paper an ultrasensitive method to determine toxicity due to pesticides in a glass lab-on-a-chip by means of enzymatic inhibition of acetylcholinesterase immobilised on magnetic beads is described. The reproducible insertion of a controlled amount of enzyme-coupled magnetic beads inside the chip channel and their immobilisation in a capture region with the aid of a magnetic field has been optimised. This procedure enables the easy renewal of the biosensing material after each determination in a highly reproducible manner. Several operational parameters such as the working potential for the selective detection of thiocholine (TCh) on a platinum disc electrode, the TCh detection reproducibility and sensitivity, the electroosmotic flow driving voltage and the inhibition time were also evaluated or optimised. The detection of carbofuran (one of the most toxic carbamate pesticides) has been achieved down to the nanomolar level.

Sensitive Aflatoxin B1 Determination Using a Magnetic Particles-Based Enzyme-Linked Immunosorbent Assay

A magnetic particle-based enzyme-liked immunosorbent assay (mp-ELISA) has been developed as new an alternative immunoassay for Aflatoxin B1 determination. The method is based on conventional competitive ELISA whereby the anti-Aflatoxin B1 antibody is immobilized on the magnetic particles' surface. The influence of the antibody type as well as antibody immobilization on the magnetic beads surface was investigated in detail. Also, optimum values for the general parameters of the method (e.g. tracer concentration, type of antibody, and incubation time) were established. Finally, a sensitive immunoassay method (mp-ELISA) was performed for Aflatoxin B1 determination at ppt level (LOD = 1 ppt Aflatoxin B1).

Binding of nontarget microorganisms from food washes to anti-Salmonella and anti-E. coli O157 immunomagnetic beads: most probable composition of background Eubacteria

We present herein the composition of bacterial communities occurring in ground chicken and the changes which arise in these populations based upon nonselective partitioning by commercially-available Dynal anti-Salmonella and anti-E. coli O157 immunomagnetic beads (IMB). Our enumeration and colony selection protocol was based upon a 6 × 6 drop plate method (n = 18 for each 25-g sub-sampling) using a dilution which resulted in ca. 4-8 colonies per drop. An average of 82 ± 13 colonies were selected from three 25-g ground chicken subsamplings per batch, each of which was repeated seasonally for one year. DNA was extracted from each colony and the composition of Eubacteria in each of these harvests was determined by sequence-based identification of 16S rDNA amplicons. The Gram-positive bacteria Brochothrix thermosphacta and Carnobacterium maltaromticum were the most commonly found organisms in both the total chicken wash (PBS) and in the IMB-bound (PBS-washed) fractions. The remaining background organisms which also adhered to varying degrees to commercial IMBs were: Pseudomonas oleovorans, Acinetobacter lwoffi, Serratia spp., and one Rahnella spp. A large number of the organisms were also cladistically evaluated based on rDNA basepair disparities: all Brochothrices were monophyletic; twelve different Pseudomonads were found along with eight Carnobacteria, seven Acinetobacteres, four Serratiae, and two Rahnellae. Carnobacterium alone showed an IMB-based concentration enhancement (ca. two to sixfold).

Determination of tryptophan and histidine by adsorptive cathodic stripping voltammetry using H-point standard addition method

A sequential method is proposed for the determination of tryptophane and histidine by adsorptive cathodic stripping voltammetry using standard addition and H-point standard addition method (HPSAM). The complexes of copper(II) with the amino acids were accumulated onto the surface of a hanging mercury drop electrode for 60s. Then the preconcentrated complexes were reduced by square wave voltammetry and the peak currents were measured. The effect of various parameters such as pH, concentration of copper, accumulation potential, accumulation time and scan rate on the sensitivity were studied by one-at-a time and artificial neural network. Under the optimized conditions, the peak currents at about +0.05 to -0.30 V is proportional to the concentration of tryptophan and histidine over the concentration ranges of 5-220 and 100-1200 nM, respectively. Optimization of the parameters by one-at-a time showed that at accumulation potential of 0.10 V (versus Ag/AgCl reference electrode) the peak current is proportional only to the concentration of tryptophan and histidine does not have any contribution to the current. The optimization results by artificial neural network showed that at accumulation potential of -0.06 V (versus Ag/AgCl) the peak current is proportional to the both concentrations of tryptophan and histidine. Therefore, the method of H-point standard addition has been used for resolving overlap voltamograms for determination of histidine in the present of tryptophane. The method was successfully applied to the determination of tryptophan and histidine in synthetic and real samples.

Evaluation of commercial immunoassays for the detection of estrogens in water by comparison with high-performance liquid chromatography tandem mass spectrometry HPLC–MS/MS (QqQ)

In this work four different commercially available enzyme-linked immunosorbent assays (ELISA) (from Japan EnviroChemicals, Ltd., Tokyo, Japan) were evaluated in terms of performance for the rapid screening of estrogens in different water matrices, including natural and spiked samples from urban wastewater, river water and ground water. All four test kits are based on monoclonal antibodies. The compounds detected by these immunoassays are (1) 17-beta-estradiol, (2) estrone, (3) 17-alpha-ethynyl estradiol and (4) estrogens in general, with high recognition properties for 17-beta-estradiol, estrone and estriol. Standards were prepared in water containing 10% (v/v) methanol. The IC50 (corresponding to the 50% of the effective concentration) values, the dynamic ranges, and the limits of detection of the ELISA kits were 0.060-0.304 microg/L, 0.05-5 microg/L and 0.05 microg/L, respectively. All samples were extracted by solid-phase extraction (SPE) beforehand, and the evaluation was carried out by comparing the results obtained by ELISA with those obtained by HPLC-MS/MS using a triple quadrupole (QqQ) instrument. In addition, two different solid-phase extraction procedures were carried out and compared. Except for moderate overestimation in the results observed with the ELISA kits in the analysis of complex wastewater samples, the results obtained using all of the tested techniques were generally in very good agreement.

Electrochemical microbead-based immunoassay using an (eta5-cyclopentadienyl)tricarbonylmanganese redox marker bound to bovine serum albumin

A first example of the solid-phase immunoassay of a high-weight antigen bovine serum albumin (BSA) using an (eta(5)-cyclopentadienyl)tricarbonylmanganese (cymantrene) redox probe is presented. The electrochemical detection is based on the impedance measurements of a one-electron reversible reduction of the organometallic probe. The microbead-based immunoassay is discussed for two types of microbeads with different diameters (2.5 and 90 microm) and capabilities to bind the immunoglobulins (2.4 and 10 microg/mg of beads). The use of larger agarose microbeads allows the formation of an antigen-antibody complex at the surface of microbeads directly dispersed in the analyzed solution. No additional separation step is necessary for the electrochemical competitive immunoassay analysis of BSA. The presence of agarose beads in the analyzed solution has no effect on the electrochemical signal from labeled BSA released from the antigen-antibody complex.

Simple Bead Injection-Flow Injection System for the Determination of Copper

We demonstrate the extended application of a simple bead injection-flow injection system with a modified simple colorimetric detection unit for the determination of low amount of Cu2+ in samples of different matrices (water and supplement tablet samples) with minimal sample pretreatment by employing ammonium pyrrolidinedithiocarbamate (APDC) reagent.

Blocking nonspecific adsorption of native food-borne microorganisms by immunomagnetic beads with ι-carrageenan

We present herein the partitioning characteristics of anti-Salmonella and anti-Escherichia coli O157 immunomagnetic beads (IMB) with respect to the nonspecific adsorption of several nontarget food-borne organisms with and without an assortment of well-known blocking agents, such as casein, which have been shown to be useful in other immunochemical applications. We found several common food-borne organisms that strongly interacted with both types of IMB, especially with anti-Salmonella form (av DeltaG0=-20 +/- 4 kJ mol(-1)) even in the presence of casein [1% (w/v): DeltaG0=-18 +/- 3 kJ mol(-1); DeltaDeltaG0 approximately -2 kJ mol(-1)]. However, when one of the most problematic organisms (a native K12-like E. coli isolate; DeltaG0=-19 +/- 2 kJ mol(-1)) was tested for nonspecific binding in the presence of iota-carrageenan (0.03-0.05%), there was an average decline of ca. 90% in the equilibrium capture efficiency xi (DeltaG0=-11 +/- 4 kJ mol(-1); DeltaDeltaG0 approximately -8 kJ mol(-1)). Other anionic polysaccharides (0.1% kappa-carrageenan and polygalacturonic acid) had no significant effect (av DeltaG0=-19 +/- 1 kJ mol(-1); DeltaDeltaG0 approximately 0 kJ mol(-1)). Varying iota-carrageenan from 0% to 0.02% resulted in xi significantly diminishing from 0.69 (e.g., 69% of the cells captured; DeltaG0=-19 +/- 3 kJ mol(-1)) to 0.05 (DeltaG0=-11 +/- 2 kJ mol(-1); DeltaDeltaG0 approximately -9 kJ mol(-1)) at about 0.03% iota-carrageenan where xi leveled off. An optimum blocking ability was achieved with 0.04% iota-carrageenan suspended in 100 mM phosphate buffer. We also demonstrated that the utilization of iota-carrageenan as a blocking agent causes no great loss in the IMBs capture efficiency with respect to the capture of its target organisms, various salmonellae.