J. Ballesta-Claver

A Portable Luminometer with a Disposable Electrochemiluminescent Biosensor for Lactate Determination

A hand-held luminometer for measuring electrochemiluminescence (ECL) for lactate determination and based on one-shot biosensors fabricated using screen-printed electrodes is described. The lactate recognition system is based on lactate oxidase and the transduction system consists of electro-oxidation of luminol, with all the reagents immobilized in a Methocel membrane. The membrane composition and reaction conditions have been optimized to obtain adequate sensitivity. The luminometer is based on a large silicon photodiode as detector and includes a programmable potentiostat to initialize the chemical reaction and signal processing circuitry, designed to acquire a low level photocurrent with offset cancelation, low pass filtering for noise attenuation and adjustable gain up to 1012 V/A. The one-shot biosensor responds to lactate rapidly, with an acquisition time of 2.5 min, obtaining a linear dependence from 8 × 10−6 to 2 × 10−4 M, a detection limit of 2.4 × 10−6 M and a sensor-to-sensor reproducibility (relative standard deviation, RSD) of around 7–10 % at the medium level of the range.

Disposable biosensor based on cathodic electrochemiluminescence of tris(2,2-bipyridine)ruthenium(II) for uric acid determination.

A new method for uric acid (UA) determination based on the quenching of the cathodic ECL of the tris(2,2-bipyridine)ruthenium(II)-uricase system is described. The biosensor is based on a double-layer design containing first tris(2,2-bipyridine)ruthenium(II) (Ru(bpy)3(2+)) electrochemically immobilized on graphite screen-printed cells and uricase in chitosan as a second layer. The uric acid biosensing is based on the ECL quenching produced by uric acid over the cathodic ECL caused by immobilized Ru(bpy)3(2+) in the presence of uricase. The use of a -1.1 V pulse for 1s with a dwelling time of 10s makes it possible to estimate the initial enzymatic rate, which is used as the analytical signal. The Stern-Volmer type calibration function shows a dynamic range from 1.0×10(-5) to 1.0×10(-3)M with a limit of detection of 3.1×10(-6)M and an accuracy of 13.6% (1.0×10(-4)M, n=5) as relative standard deviation. Satisfactory results were obtained for urine samples, creating an affordable alternative for uric acid determination.

One-shot lactate chemiluminescent biosensor

A new chemiluminescence-based one-shot biosensor for lactate is described. The lactate recognition system is based on lactate oxidase (LOx) and the transduction system consists of luminol, peroxidase from Arthromyces ramosus (ARP) and metallic aluminum, all immobilized in a polyion complex membrane. The measurement of the chemiluminescence in a luminometer when 1 mL of sample is injected into a conventional cell containing the disposable sensing membrane makes it possible to determine lactate. The compositions of the membrane and reaction conditions have been optimized to obtain adequate sensitivity. The one-shot biosensor responds to lactate rapidly, with the typical CL acquisition time being 2 min, with a linearized logarithmic dependence whose dynamic range was from 5 x 10(-5) to 4 x 10(-3) with a detection limit of 9.2 x 10(-6)M and a sensor-to-sensor reproducibility (relative standard deviation, R.S.D.) of 5.5% at the medium level of the range. The performance of the chemiluminescent one-shot biosensor was tested for the analysis of lactate in yoghurt, validating the results against an enzymatic reference procedure. The proposed method is quick, inexpensive and sensitive and uses conventional CL instrumentation.