Sol-gel based sensor for selective formaldehyde determination

We report the development of transparent sol–gels with entrapped sensitive and selective reagents for the detection of formaldehyde. The sampling method is based on the adsorption of formaldehyde from the air and reaction with β- diketones (for example acetylacetone) in a sol–gel matrix to produce a yellow product, lutidine, which was detected directly. The proposed method does not require preparation of samples prior to analysis and allows both screening by visual detection and quantitative measurement by simple spectrophotometry. The detection limit of 0.03 ppmv formaldehyde is reported which is lower than the maximum exposure concentrations recommended by both the World Health Organisation (WHO) and the Occupational Safety and Health Administration (OSHA). This sampling method was found to give good reproducibility, the relative standard deviation at 0.2 and 1 ppmv being 6.3% and 4.6%, respectively. Other carbonyl compounds i.e. acetaldehyde, benzaldehyde, acetone and butanone do not interfere with this analytical approach. Results are provided for the determination of formaldehyde in indoo

Sub-attomolar detection of cholera toxin using a label-free capacitive immunosensor

A label-free immunosensor for the direct detection of cholera toxin (CT) at sub-attomolar level has been developed based on potential-step capacitance measurements. Anti-CT antibody was adsorbed on gold nanoparticles (AuNPs) incorporated on a polytyramine-modified gold electrode. The concentration of CT was determined by detecting the change of capacitance caused by the formation of antibody-antigen complexes. By using AuNPs adsorbed to the sensing surface, the signal was dramatically increased leading to a significantly more sensitive assay. In fact, under optimum conditions the immunosensor could detect CT concentration with a limit of detection of 9 x 10(-20) M or 0.09 aM, with a dynamic range between 0.1 aM and 10 pM. Good analytical reproducibility could be obtained by injecting CT up to 36 times with an RSD of 2.5%. In addition, good performance of the developed immunosensor was achieved when applied to turbid water samples collected from a local stream that were spiked with CT. (c) 2010 Elsevier B.V. All rights reserved

A reusable capacitive immunosensor for carcinoembryonic antigen (CEA) detection using thiourea modified gold electrode

A capacitive immunosensor based on a self-assembled monolayer (SAM) of thiourea on gold electrode has been developed. Anti-carcinoembryonic antigen (anti-CEA) was immobilized on a self-assembled thiourea monolayer (SATUM) via covalent coupling. Under optimum conditions, the decrease in capacitive signal when carcinoembryonic antigen (CEA) standard was injected could be determined with a detection limit of 10 pg ml(-1) and linearity in the range of 0.01-10 ng ml(-1). The immobilized anti-CEA on SATUM gold electrode was stable and after regeneration good reproducibility of the signal could be obtained tip to 45 times with an RSD lower than 3.4%. Good agreement was obtained when CEA concentrations of human serum samples determined by the flow injection capacitive immunosensor system were compared to those obtained using an enzyme linked fluorescent assay (ELFA) method (P < 0.05). (c) 2006 Elsevier B.V. All rights reserved

Microbial biosensor for the analysis of 2,4-dichlorophenol

A flow injection cell-based biosensor was constructed for 2,4-dichlorophenol (DCP) analysis by using a Clark-type oxygen electrode as a transducer. A mixed bacterial culture capable to biodegrade DCP was immobilized between a Teflon membrane and a dialysis membrane and attached to the oxygen electrode. Optimization of the flow rate, the injection volume, the carrier buffer concentration, and pH was carried out. Under optimum conditions (100 mM phosphate buffer, pH 7.50; flow rate 0.10 mL min(-1); sample volume 100 mL), the sensor response was linear between 0.01 and 0.30 mM DCP. The detection limit was 0.02 mM DCP, and the sensor was quite stable during 5 days of operation

Potentiometric detection of DNA hybridization

The use of potentiometric microsensors is demonstrated here for the first time to detect DNA hybridization. Cadmium sulfide nanocrystal labels bound on a secondary oligonucleolide are dissolved and detected with cadmium-selective microelectrodes exhibiting DNA detection limits of ca. 2 fmol in a 200 mu sample

Ion sensing pencil: Draw your own sensor

We demonstrate for the first time the concept of ion sensing pencil (ISP). The pencil’s lead carries chemical sensing functionality and is constructed by compression of graphite and zeolite, while the clutch is prepared by 3D printing. The ISP can be used to draw a chemical sensor by simple abrasion onto a hydrophobic surface. The ISP can be stored at home, used immediately off-the-shelf without any handling prior to measurements. It’s simple preparation, handling, and measuring protocols offer the possibility of integration into large scale sensor networks or to be offered to the general public for use at home using readout devices already present at many homes. We demonstrate the chemical functionality of ISP by producing 14 ISPs prepared by compression of graphite and one of 14 different zeolites individually in 60:40 wt%. These ISPs are then used to draw electrodes which were characterized in analogy to ion-selective electrodes. The ISP-drawn electrodes were utilized as a multi-sensor array for the determination of water quality in a model sample, which is a first reported case of using zeolite-based electrodes in multisystem arrays, followed by the demonstration of their potential to be used by non-trained personnel. The implementation ISPs in potentiometric detection holds promise for further development of inexpensive and accessible tools for obtaining chemical information in areas where utilization of chemical sensors is currently limited

Aptamer-Based Potentiometric Measurements of Proteins Using Ion-Selective Microelectrodes

We here report on the first example of an aptamer-based potentiometric sandwich assay of proteins. The measurements are based on CdS quantum dot labels of the secondary aptamer, which were determined with a novel solid-contact Cd2+-selective polymer membrane electrode after dissolution with hydrogen peroxide. The electrode exhibited cadmium ion detection limits of 100 pM in 100 mL samples and of 1 nM in 200 microwells, using a calcium-selective electrode as a pseudoreference electrode. As a prototype example, thrombin was measured in 200 samples with a lower detection limit of 0.14 nM corresponding to 28 fmol of analyte. The results show great promise for the potentiometric determination of proteins at very low concentrations in microliter samples

Striped Alloy Nanowire Optical Reflectance Barcodes Prepared from a Single Plating Solution

The preparation of multisegment alloy nanowire barcodes with optical-reflectance striping patterns and large coding capacity using a template-assisted electro-deposition from a single gold-silver plating solution, was presented. A template-assisted electro-deposition method can be applied in a predetermined order for different duration for producing alloy segment of controlled length. The nanowire was prepared from an 85/15 (v/v) Au/Ag plating solution by applying different potentials. Barcodes were prepared by varying the deposition conditions, while using the same plating solution. The multipotential templated deposition from plating solution resulted in distinct stepwise variation of the alloy composition along the length of the nanowires. The reflectance intensity of barcodes was determined using the highest intensity value corresponding to a prevalently silver segment deposited at -0.50 V

Printable Heterostructured Bioelectronic Interfaces with Enhanced Electrode Reaction Kinetics by Intermicroparticle Network

Printable organic bioelectronics provide a fast and cost-effective approach for the fabrication of novel biodevices, while the general challenge is to achieve optimized reaction kinetics at multiphase boundaries between biomolecules and electrodes. Here, we present an entirely new concept based on a modular approach for the construction of heterostructured bioelectronic interfaces by using tailored functional “biological microparticles” combined with “transducer microparticles” as modular building blocks. This approach offers high versatility for the design and fabrication of bioelectrodes with a variety of forms of interparticle spatial organization, from layered-structures to more advance bulk heterostructured architectures. The heterostructured biocatalytic electrodes delivered twice the reaction rate and a six-fold increase in the effective diffusion kinetics in response to a catalytic model using glucose as the substrate, together with the advantage of shortened diffusion paths for reactants between multiple interparticle junctions and large active particle surface. The consequent benefits of this improved performance combined with the simple means of mass production are of major significance for the emerging printed electronics industry