Piezoelectric immunosensor for bisphenol A based on signal enhancing step with 2-methacrolyloxyethyl phosphorylcholine polymeric nanoparticle

Enantioseparation/Recognition based on nano techniques/materials

Enantiomers show different behaviors in interaction with the chiral environment. Due to their identical chemical structure and their wide application in various industries, such as agriculture, medicine, pesticide, food, and so forth, their separation is of great importance. Today, the term "nano" is frequently encountered in all fields. Technology and measuring devices are moving towards miniaturization, and the usage of nanomaterials in all sectors is expanding substantially. Given that scientists have recently attempted to apply miniaturized techniques known as nano-liquid chromatography/capillary-liquid chromatography, which were originally accomplished in 1988, as well as the widespread usage of nanomaterials for chiral resolution (back in 1989), this comprehensive study was developed. Searching the terms "nano" and "enantiomer separation" on scientific websites such as Scopus, Google Scholar, and Web of Science yields articles that either use miniaturized instruments or apply nanomaterials as chiral selectors with a variety of chemical and electrochemical detection techniques, which are discussed in this article.

Advances in immunosensor technology

In recent years, advances in immunosensor device fabrication have significantly expanded the use of this technology in a broad range of applications including clinical diagnosis, food analysis, quality control, environmental studies and industrial monitoring. The most important aspect in fabrication is to obtain a design that provides a low detection limit. The utilization of nanomaterials as a label, catalyst and biosensing transducer is, perhaps, the most popular approach in ultrasensitive devices. This chapter reviews recent advances in immunosensor fabrication and summarizes the most recent studies. Strategies employed to significantly improve sensitivity and specificity of immunosensor technology and the advantages and limitations thereof are explored.

Polymeric immunosensors for tumor detection

Cancer is a broad-spectrum disease which is spread globally, having high mortality rates. This results from genetic, epigenetic and molecular abnormalities caused by various mutations. The main reason behind this critical problem lies in its diagnostics, the late detection of the disease is the root cause of all this. This can be managed well by the timely diagnosis of cancer by means of the tumor biomarkers present in the body fluids such as serum, blood, and urine. These tumor biomarkers are present in normal conditions as well, but their concentrations are altered in the presence of a malignant tumor. Prolonged studies have reported that immunosensors can be used to detect the minimal amount of biomarkers present in the sample and also provides point-of-care detection. The recent investigations demonstrated the use of polymers along with immunosensors for enhancing their selectivity and sensitivity towards the biomarkers and making them even more efficient. This review focuses on the variety of tumor biomarkers, different types of immunosensors and polymeric immunosensors using different polymers like polypyrrole, polyaniline, PHEMA, etc.

Bisphenol A Sensors on Polyimide Fabricated by Laser Direct Writing for Onsite River Water Monitoring at Attomolar Concentration

This work presents an aptamer-based, highly sensitive and specific sensor for atto- to femtomolar level detection of bisphenol A (BPA). Because of its widespread use in numerous products, BPA enters surface water from effluent discharges during its manufacture, use, and from waste landfill sites throughout the world. On-site measurement of BPA concentrations in water is important for evaluating compliance with water quality standards or environmental risk levels of the harmful compound in the environment. The sensor in this work is porous, conducting, interdigitated electrodes that are formed by laser-induced carbonization of flexible polyimide sheets. BPA-specific aptamer is immobilized on the electrodes as the probe, and its binding with BPA at the electrode surface is detected by capacitive sensing. The binding process is aided by ac electroosmotic effect that accelerates the transport of BPA molecules to the nanoporous graphene-like structured electrodes. The sensor achieved a limit of detection of 58.28 aM with a response time of 20 s. The sensor is further applied for recovery analysis of BPA spiked in surface water. This work provides an affordable platform for highly sensitive, real time, and field-deployable BPA surveillance critical to the evaluation of the ecological impact of BPA exposure.

A Novel Signal-Amplified Immunoassay for the Detection of C-Reactive Protein Using HRP-Doped Magnetic Nanoparticles as Labels with the Electrochemical Quartz Crystal Microbalance as a Detector

A novel horseradish peroxidase- (HPR-) doped magnetic core-shell Fe3O4@SiO2@Au nanocomposites (Fe-Au MNPs) were employed on immunoassay for the determination of C-reactive protein (CRP) based on a electrochemical quartz crystal microbalance detector (EQCM). Firstly, the secondary CRP antibody and HRP were both immobilized on the Fe-Au MNPs (Fe-Au MNPs-anti-CRP2/HRP) as a signal tag. Secondly, the above tag and the primary antibody (anti-CRP1) in the bottom of 96-well microtiter plate were employed to conjugate with a serial of CRP concentrations to produce a sandwich immunocomplex. Thirdly, the immunocomplex solution was subsequently exposed to 3, 3'-diaminobenzidine (DAB) in the presence of H2O2, resulting in an insoluble product. When the precipitation solution was dripped on EQCM, it can achieve a decrease of frequency of crystal (Δf). The amount of Δf was proportional to (CRP) from 0.003 to 200 ng mL(-1) with a low detection limit of 1 pg mL(-1). Compared with the enzyme-linked immunosorbent assay (ELISA), the immunoassay shows greatly improved sensitivity due to the significant amount of HRP labeled on signal tag. It also has good specificity and low sample consumption, which is expected to be a benefit for the CRP screening in early diagnosis of cardiovascular disease.

A facile electrochemical sensor for nonylphenol determination based on the enhancement effect of cetyltrimethylammonium bromide

A facile electrochemical sensor for the determination of nonylphenol (NP) was fabricated in this work. Cetyltrimethylammonium bromide (CTAB), which formed a bilayer on the surface of the carbon paste (CP) electrode, displayed a remarkable enhancement effect for the electrochemical oxidation of NP. Moreover, the oxidation peak current of NP at the CTAB/CP electrode demonstrated a linear relationship with NP concentration, which could be applied in the direct determination of NP. Some experimental parameters were investigated, such as external solution pH, mode and time of accumulation, concentration and modification time of CTAB and so on. Under optimized conditions, a wide linear range from 1.0 × 10⁻⁷ mol·L⁻¹ to 2.5 × 10⁻⁵ mol·L⁻¹ was obtained for the sensor, with a low limit of detection at 1.0 × 10⁻⁸ mol·L⁻¹. Several distinguishing advantages of the as-prepared sensor, including facile fabrication, easy operation, low cost and so on, suggest a great potential for its practical applications.

Electrochemical oxidation of glucose using mutant glucose oxidase from directed protein evolution for biosensor and biofuel cell applications

In this study, electrochemical characterisation of glucose oxidation has been carried out in solution and using enzyme polymer electrodes prepared by mutant glucose oxidase (B11-GOx) obtained from directed protein evolution and wild-type enzymes. Higher glucose oxidation currents were obtained from B11-GOx both in solution and polymer electrodes compared to wt-GOx. This demonstrates an improved electrocatalytic activity towards electrochemical oxidation of glucose from the mutant enzyme. The enzyme electrode with B11-GOx also showed a faster electron transfer indicating a better electronic interaction with the polymer mediator. These encouraging results have shown a promising application of enzymes developed by directed evolution tailored for the applications of biosensors and biofuel cells.

Square wave voltammetry versus electrochemical impedance spectroscopy as a rapid detection technique at electrochemical immunosensors

Square wave voltammetry (SWV) was compared to electrochemical impedance spectroscopy (EIS) in developing a label-free electrochemical immunosensor for the hormone estradiol. The immunosensor consists of a Au electrode anchored with a Au nanoparticle|thiolated Protein G-scaffold to facilitate immobilisation of an enhanced quantity of an almost uprightly aligned anti-estradiol capture antibody. Competitive immunoassays between an estradiol-bovine saline albumin complex and free estradiol in a sample were then promoted at the immunosensor. Next, SWV and EIS of [Fe(CN)(6)](3-/4-) were sequentially conducted at the immunosensor. SWV yielded familiar peak-shaped voltammograms with the peak currents readily employable in establishing calibration. A dynamic range up to approximately 1200 pg mL(-1) and a detection limit of 18 pg mL(-1) estradiol were achieved. In EIS, an electron transfer resistance estimated from the Nyquist plots was used in the calibration experiments. A comparable dynamic range up to approximately 1000 pg mL(-1) and a detection limit of 26 pg mL(-1) estradiol were obtained. However, a significantly 10 times longer analysis time and substantial effort were required to complete the EIS determinations relative to SWV. Moreover, a large amount of EIS data involving phase angle was collected but ignored because they would not contribute any useful information to quantitative determination. Overall, SWV was determined to be a more rapid, efficient, effective and low cost detection technique than EIS at label-free electrochemical immunosensors.

Enzymatic determination of BPA by means of tyrosinase immobilized on different carbon carriers

Different tyrosinase carbon paste modified electrodes to determine bisphenol A (BPA) concentration in aqueous solutions have been constructed. Variables examined were in the carbon paste composition and in particular: (i) the immobilized enzyme amount; (ii) the carbon type (powder, single or multi-walled nanotubes); (iii) the nature of the pasting oil (mineral oil, hexadecane and dodecane). For each biosensor type the amperometric response was evaluated with reference to the linear range and sensitivity. Constant reference has been made to the amperometric signals obtained, under the same experimental conditions, towards the catechol, a specific phenolic substrate for tyrosinase. The most efficient biosensors were those constructed by using the following composition for the carbon paste: 10% of tyrosinase, 45% of single wall carbon nanotubes (SWCN) and 45% of mineral oil. This biosensor formulation displayed the following electrochemical characteristics: a sensitivity equal to 138 microA/mM, LOD of 0.02 microM (based on three times the S/N ratio), linear range of 0.1-12 microM and response time of 6 min. This experimental work represents a first attempt at construction of a new carbon nanotube-tyrosinase based biosensor able to determine the concentration of BPA, one of the most ubiquitous and hazardous endocrine disruptors which can pollute the drinking and surface water, as well as many products of the food chain.

Microfluidic flow control on charged phospholipid polymer interface

A type of charged phospholipid polymer biointerface was constructed on a quartz microfluidic chip to control the electroosmotic flow (EOF) and to suppress non-specific protein adsorption through one-step modification. A negatively charged phospholipid copolymer containing 2-methacryloyloxyethyl phosphorylcholine (MPC), n-butyl methacrylate (BMA), potassium 3-methacryloyloxypropyl sulfonate (PMPS) and 3-methacryloxypropyl trimethoxysilane (MPTMSi) moieties (referred to as PMBSSi) was synthesized to introduce such phosphorylcholine segments as well as surface charges onto the silica-based microchannels via chemical bonding. At neutral pH, the homogenous microchannel surface modified with 0.3 wt% PMBSSi in alcoholic solution, retained a significant cathodic EOF ((1.0 +/- 0.1) x 10(-4) cm(2) V(-1) s(-1)) with approximately one-half of the EOF of the unmodified microchannel ((1.9 +/- 0.1) x 10(-4) cm(2) V(-1) s(-1)). Along with another non-charged copolymer (poly(MPC-co-MPTMSi), PMSi), the regulation of the surface charge density can be realized by adjusting the concentration of PMBSSi or PMSi initial solutions for modification. Coincidently, the zeta-potential and the EOF mobility at neutral pH showed a monotonically descending trend with the decrease in the charge densities on the surfaces. This provides a simple but feasible approach to controlling the EOF, especially with regard to satisfying the requisites of miniaturized systems for biological applications requiring neutral buffer conditions. In addition, the EOF in microchannels modified with PMBSSi and PMSi could maintain stability for a long time at neutral pH. In contrast to the EOF in the unmodified microchannel, the EOF in the modified microchannel was only slightly affected by the change in pH (from 1 to 10). Most importantly, although PMBSSi possesses negative charges, the non-specific adsorptions of both anionic and cationic proteins (considering albumin and cytochrome c, respectively, as examples) were effectively suppressed to a level of 0.15 microg cm(-2) and lesser in the case of the 0.3 wt% PMBSSi modification. Consequently, the variation in the EOF mobility resulting from the protein adsorption was also suppressed simultaneously. To facilitate easy EOF control with compatibility to biomolecules delivered in the microfluidic devices, the charged interface described could provide a promising option.

Quartz crystal microbalance immunosensors for environmental monitoring

This paper presents discussion of quartz crystal microbalance (QCM) immunosensors for environmental monitoring. Factors limiting the practical application of antibodies to analytical problems are also presented. Among several candidates for the QCM immunosensor device, selected QCM devices and oscillating circuits were tested thoroughly and developed to obtain highly stable and sensitive frequency signals. The biointerface of QCM immunosensor was designed and controlled to immobilize antibody on the QCM surface, to reduce non-specific binding and to suppress denaturation of immobilizing antibody by self-assembled monolayer technique and artificial phospholipid (2-methacryloyloxyethyl phosphorylcholine (MPC)) polymer. MPC polymer as a antibody-stabilizing reagent was added to reduce non-specific binding of the antigen solution and stabilize the immunologic activity of the antibody-immobilized QCM. In addition, it provides examples for detection and quantitation of environmental samples using QCM immunosensors. The analytical results for fly ash extracted samples of dioxins using the QCM immunosensor indicated a good relationship with GC/MS methods. The integrating protocols of the competitive immunoassay and signal-enhancing step are for detecting low molecular analytes with extremely low detection limits using an QCM immunosensor. Furthermore, its detect limitation was extended from 0.1 to 0.01 ng/ml by the signal-enhancing step when the anti-bisphenol-A antibody conjugated MPC polymeric nanoparticles was used. The QCM immunosensor method has demonstrated its effectiveness as an alternative screening method for environmental monitoring because these results were compared with results obtained through environmental monitoring methods such as ELISA and GC/MS.