Development of an electrochemical ELISA for the screening of 17 beta-estradiol and application to bovine serum

Development of a Protein Microarray Chip with Enhanced Fluorescence for Identification of Semen and Vaginal Fluid

The detection of body fluids has been used to identify a suspect and build a criminal case. As the amount of evidence collected at a crime site is limited, a multiplex identification system for body fluids using a small amount of sample is required. In this study, we proposed a multiplex detection platform using an Ag vertical nanorod metal enhanced fluorescence (MEF) substrate for semen and vaginal fluid (VF), which are important evidence in cases of sexual crime. The Ag nanorod MEF substrate with a length of 500 nm was fabricated by glancing angle deposition, and amino functionalization was conducted to improve binding ability. The effect of incubation time was analyzed, and an incubation time of 60 min was selected, at which the fluorescence signal was saturated. To assess the performance of the developed identification chip, the identification of semen and VF was carried out. The developed sensor could selectively identify semen and VF without any cross-reactivity. The limit of detection of the fabricated microarray chip was 10 times better than the commercially available rapid stain identification (RSID) Semen kit.

A novel electrochemical enzyme biosensor for detection of 17β-estradiol by mediated electron-transfer system

An extremely sensitive enzyme sensor for detection of 17β-estradiol based on electropolymerized L-lysine molecules on a glassy carbon electrode (GCE) modified with critic acid@graphene (CA-GR) and cross-linked with laccase enzyme has been developed in this work. As the laccase immobilization, glutaraldehyde was chosen as cross-linker through the groups reactions. The novel enzyme sensor could recognize and determinate 17β-estradiol effectively. The morphology of the enzyme modified electrode was characterized by transmission electron microscopy (TEM) and electron microscopy (SEM). The amino interaction between cross-linker and enzyme was characterized by Fourier transform infrared spectroscopy (FTIR). Under the optimal experimental conditions, good linear relationships were achieved in the range of 4 × 10^-13 - 5.7 × 10^-11 M and a limit of detection as low as 1.3 × 10^-13 M. Moreover, the enzyme sensor exhibited good reproducibility, stability and high selectivity to 17β-estradiol. Excellent performance was showed in the human urine samples analysis, thus confirming great prospect for further application in clinic diagnosis and biological research.

The Comamonas testosteroni steroid biosensor system (COSS)--reflection on other methods

Natural and synthetic steroid hormones are released uncontrolled into the environment and are considered as pollutants with regard to their endocrine activity and negative influence on all kind of organisms. Due to their widespread presence, endocrine activity even at low concentrations, and their potential adverse effects in both the environment and human health, there is an increasing need for the development of rapid, sensitive and quantitative techniques for measuring trace levels of these steroids. In addition to classical analytical methods like GC-MS, LC-MS and others, several techniques have been established that are based on human nuclear steroid receptors as reporter systems. However, many of these systems require human or yeast cell culture and are therefore time consuming and expensive, while others suffer from too low sensitivity or cover only one specific steroid compound. These are some of the main reasons that limit current techniques for environmental application. The remarkable ability of certain microorganisms to transform and degrade the steroid nucleus and to respond with the induced expression of steroid regulated genes lead us to explore, whether the steroid signalling machinery of Comamonas testosteroni could be used to construct a steroid sensoring system that is sensitive, rapid, easy to perform, and which could also be applied to detect environmental steroid mixtures at low concentrations. Both whole C. testosteroni mutant cells as well as the cytosol thereof were used as new and sensitive fluorescence based biosensor systems for the successful determination and quantification of a variety of different steroids. We could show that our COSS (Comamonas testosteroniSteroid Sensor) is able to detect testosterone, estradiol and cholesterol in concentrations of 29pg/mL, 0.027pg/mL, and 9.7pg/mL, respectively. The sensitivity of the COSS together with the fact that it is very fast, reproducible and can be used for high-throughput screening in a microplate format makes it suitable for the detection of single steroid hormones or steroid hormone mixtures in environmental samples at low costs. In summary, the COSS is able to detect steroid hormone effects at the molecular level through activation of bacterial steroid-sensing systems. In the future, it may be further developed as a useful tool for the integrative assessment of ecotoxicological potentials caused by hormonally active agents and endocrine-disrupting compounds.

Direct electrochemical detection of trichothecenes in wheat samples using a 96-well electrochemical plate coupled with microwave hydrolysis

The use of a 96-well electrochemical plate for the fast and sensitive detection of deoxynivalenol and nivalenol in wheat samples is shown. Deoxynivalenol and nivalenol are hydrolysed using a microwave hydrolysis procedure (2 min) which leads to the production of electroactive compounds that can be sensitively detected by the use of cheap screen-printed electrodes. A procedure of extraction with aqueous acetonitrile and a clean-up step was demonstrated to be suitable for the application with wheat samples providing suitable detection limit (LOD=1.1 µg/g) and working range (2-20 µg/g) for the determination of deoxynivalenol in cereals for feed consumption.

Preparation of screen-printed electrochemical immunosensors for estradiol, and their application in biological fluids

The method of fabrication of a prototype electrochemical immunosensor for estradiol (E2) is described. Methodologies are also given for colorimetric assays, which can be used to verify and optimize reagent performance, prior to their use in the electrochemical immunoassay: these include an E2 ELISA and a colorimetric assay performed on the immunosensor surface. The electrochemical immunosensor system uses screen-printed carbon electrodes (SPCEs) upon which antibody against E2 is immobilized. Antibodies (rabbit anti-mouse IgG, then monoclonal mouse anti-E2) are immobilized by passive adsorption onto the working electrode surface. A competitive immunoassay is then performed using an alkaline-phosphatase-labeled E2 conjugate. Electrochemical measurements are performed using differential pulse voltammetry (DPV) to detect the production of 1-naphthol from 1-naphthyl phosphate. The calibration plot of DPV peak current vs. E2 concentration shows a measurable range of 25-500 pg/mL with a detection limit of 50 pg/mL. The immunosensor can be applied to the determination of E2 in spiked serum, following an extraction step with diethyl ether.

A disposable immunosensor for detection of 17β-estradiol in non-extracted bovine serum

This paper reports the assembly of a disposable immunosensor based on the direct competitive enzyme-linked immunosorbent assay (ELISA), for simple and fast measurement of 17beta-estradiol (17beta-E2) in bovine serum, using screen-printed electrodes (SPEs) and a Palm-Sens portable electrochemical detector. The immunosensor strip was assembled immobilising, by passive adsorption, anti-rabbit IgG onto the surface of the working SPE electrode. After the interaction between anti-rabbit IgG and rabbit anti-17beta-E2 polyclonal antibodies (PAb), the competition was performed using 17beta-estradiol-alkaline phosphatase conjugate (17beta-E2-AP) synthesised in our laboratory. The enzymatic substrate used for signal generation was 1-naphthylphosphate and its conversion to an electroactive product (1-naphthol) was measured using differential pulse voltammetry (DPV). To develop a prototype for field measurements, the entire competitive protocol has been optimised directly in a blank non-extracted bovine serum. According to the new EU criteria established by the Commission Decision 2002/657/EC for qualitative and quantitative screening methods, the detection capability (CCbeta), was determined. The CCbeta value resulted below the action limit (40 pg mL(-1)) fixed for 17beta-E2) Spiked and real samples were analysed using the electrochemical immunostrips obtaining precision values (relative standard deviation, R.S.D.%) ranging from 8.6 to 17.0% and a recovery (R%) from 88.2 to 120.0%. Results obtained on real samples were confirmed by liquid chromatography coupled on-line with tandem mass spectrometry (LC-MS/MS) using an atmospheric pressure chemical ionisation (APCI) source and a heated nebulizer (HN) interface; this is the method currently used to confirm illegal hormone administration for regulatory purposes. The disposable immunosensor appears suitable as a screening tool for field analysis of bovine serum estradiol.

Estrogen conjugation and antibody binding interactions in surface plasmon resonance biosensing

Thioether-linked 3-mercaptopropionic acid derivatives of 17beta-estradiol and estrone were formed at the A-ring 4-position of the steroids by substitution of their 4-bromo analogues. The carboxylic acid terminal was used to link to an oligoethylene glycol (OEG) chain of 15-atoms in length. The OEG derivative of 17beta-estradiol was then in situ immobilized on a carboxymethylated dextran-coated gold sensor surface used to detect refractive index changes upon protein binding to the surface by surface plasmon propagation in a BIAcore surface plasmon resonance (SPR) instrument. Two other estradiol-OEG derivatives with Mannich reaction linkage at the 2-position and hemisuccinate linkage at the 3-position were also immobilized on the sensor surfaces for comparison. Binding performance between these immobilized different positional conjugates and monoclonal anti-estradiol antibody, raised from a 6-position conjugate, clearly demonstrated that both 2- and 4-conjugates, not conjugated through existing functional groups, gave strong antibody bindings, whereas the 3-conjugate through an existing functional group (3-OH) gave very little binding (2% compared to the 2-conjugate). Both 2- and 4-position conjugates were then applied in a highly sensitive estradiol SPR immunoassay with secondary antibody mediated signal enhancement that gave up to a 9.5-fold signal enhancement of primary antibody binding, and a detection limit of 25 pg/mL was achieved for a rapid and convenient flow-through immunoassay of estradiol.

Expression analysis of androgen-responsive genes in the prostate of veal calves treated with anabolic hormones

In order to identify indirect molecular biomarkers of anabolic treatments in veal calves, an animal experiment was performed using two combinations of growth promoters (consisting of boldenone undecylenate and estradiol benzoate, and of testosterone enantate and estradiol benzoate). We selected a set of 12 genes that are known to be androgen responsive in other mammalian species. The expression profile of this set of genes was analysed on prostate samples of veal calves using a real-time RT-PCR approach. For each selected gene the corresponding bovine sequence was obtained and a gene specific real-time assay was optimised and validated. The amplification was shown to be highly specific, linear and efficient. High reproducibility (<1%) and low-test variability (<2.5%) were also been achieved. Messenger RNA levels were quantified in prostate samples, non-parametric analysis of variance showed significant up-regulation of three genes (MAF, ESR1 and AR) and significant down-regulation of four genes (HMGCS1, HPGD, DBI, and LIM) in treated samples when compared with untreated controls. To assess the possibility of identifying hormone-treated animals by molecular means we performed a discriminant analysis that was effective in classifying treated and non-treated samples with an accuracy of 93%. Our results indicate that identification of treatment with steroid hormones in veal calves by means of gene expression analysis is a feasible approach and could be improved increasing both the number of genes and the number of controls analysed.

Biosensors for marine applications. We all need the sea, but does the sea need biosensors?

The aim of the paper is to explain the rationale behind marine biosensor applications, give an overview of measurement strategies currently employed, summarise some of the relevant available biosensor technology as well as instrumentation requirements for marine sensors and attempt a forward look at what the future might hold in terms of needs and developments. Application areas considered are eutrophication, organism detection, food safety, pollutants, trace metals and ecotoxicology. The drivers for many of these studies are discussed and the policy environment for current and future measurements is outlined.

Development of a screen-printed carbon electrochemical immunosensor for picomolar concentrations of estradiol in human serum extracts

Investigations into the development of a prototype electrochemical immunosensor for estradiol (E(2)) are described. After optimising reagent loadings in a 96-well enzyme-linked immunosorbent assay (ELISA), antibodies (rabbit anti-mouse IgG and monoclonal mouse anti-E(2)) were immobilised by passive adsorption onto the surface of screen-printed carbon electrodes (SPCEs). A competitive immunoassay was then performed using an alkaline-phosphatase (ALP)-labelled E(2) conjugate. Calibration plots for E(2) buffer standards, performed colorimetrically on the SPCEs using a para-nitrophenyl phosphate substrate solution, were in good agreement with ELISA calibration plots. Electrochemical measurements were then performed using differential pulse voltammetry (DPV) following the production of 1-naphthol from 1-naphthyl phosphate. The calibration plot of DPV peak current versus E(2) concentration showed a measurable range of 25-500 pg/ml with a detection limit of 50 pg/ml. A coefficient of variation of between 13.0 and 15.6% was obtained for repeat measurements. The immunosensor was applied to the determination of E(2) in spiked serum, following an extraction step with diethyl ether. A mean recovery for the method of 102.5% was obtained with a CV of 19.1%. The options available for further development of the sensor regarding precision, limit of detection and direct sample analysis are discussed.

Sensing the sea

The development of the 'ecosystem approach' to the management of marine systems is leading to a requirement for data to be collected with greater frequency and spatial resolution than has been necessary in the past. This is being met both by the analysis of more samples (to better describe variability and temporal change) and by the deployment of instrumented platforms that gather data over long time periods. To meet these requirements in the hostile conditions at sea, a range of sensors based on physical, chemical and biological responses is being developed. These sensors have applications in laboratory analysis of collected samples, during field studies and directly in situ at remote sites for real-time observations of environmental trends. Here, we consider the role that biosensors could have in future marine monitoring programmes.

Detection of Staphylococcus aureus enterotoxin A and B genes with PCR-EIA and a hand-held electrochemical sensor

Two electrochemical assays for detecting Staphylococcus aureus enterotoxin A and B genes were developed. The assays are based on PCR amplification with biotinylated primers, hybridization to a fluorescein-labeled probe, and detection with horseradish peroxidase-conjugated anti-fluorescein antibody using a hand-held electrochemical detector. The limit of detection (LOD) for both assays was approximately 16 copies of the sea and seb genes. The assays were evaluated in blinded studies, each with 81 samples that included genomic and cloned S. aureus DNA, and genomic DNA from Alcaligens, Bacillus, Bacteroides, Bordetella, Borkholderia, Clostridium, Comanonas, Enterobacter, Enterococcus, Escherichia, Francisella, Haemophilus, Klebsiella, Listeria, Moraxella, Neisseria, Proteus, Pseudomonas, Salmonella, Serratia, Shigella, Streptococcus, Vibrio and Yersinia species. Both assays showed 100% sensitivity. The specificity was 96% for the SEA assay and 98% for the SEB assay. These results demonstrate the feasibility of performing probe-based detection of PCR products with a low-cost, hand-held, electrochemical detection device as a viable alternative to colorimetric enzyme-linked assays of PCR products.

Separation and detection of neuroactive steroids from biological matrices

This review is based on a selection of research papers published mainly in the last decade and it describes various analytical aspects of separation and detection of neuroactive steroids in biological matrices.