The present invention relates to hybrid solgel modified electrode for use in bio-medical analysis.

BACKGROUND ART

Bio-medical analysis involves the detection of metabolites level in bodily fluid to diagnose diseases such as diabetes, renal failure and cardiovascular problems. To detect levels of these analytes in blood and urine, enzyme electrodes have been widely employed.

Although the use of enzyme electrode has the advantages of high selectivity nature of enzymatic reaction, the use of enzyme electrode has several disadvantages. The enzymes are proteins and specificity of enzymatic transformation depends on complex three-dimensional interaction between amino acid units in the enzyme. These interactions give secondary and tertiary structures of the enzyme which changes outside living cells. Consequently, enzymatic reactions deteriorate over time while giving inaccurate biosensor data.

Also, enzymes contain numerous reactive sites that may be disrupted during immobilisation step. Furthermore, enzymes are usually stored under chilled conditions which have serious limitation in deployment of mass-produced biosensors. Enzyme denaturing also seriously limits the sensor lifetime.

Due to these reasons, innovation has been made on the bio-medical analysis electrodes. At present, a prior art listed a voltammetric system for assaying biological analytes. It uses conventional enzyme method with redox-couple mediator. Glucose dehydrogenase gives selectivity towards glucose substrate and the calibration and measurement is done by cyclic voltammetry.

Another prior art listed a voltammetric ion selective biosensor which includes a method to detect ionic species in fluids, whereby the selectivity is achieved using coated conductive solid such as tetrahiafulvalene and detection is done using voltammetric method.

The present invention is made in view of the need to address the disadvantages of using enzyme electrodes while the ion selective sensors only detect ionic species while retaining voltammetric analytical method.

SUMMARY OF INVENTION The present invention proposes a hybrid solgel modified electrode, non-enzymatic biosensors that target bio-molecules present in body fluids which includes glucose, cholesterol, uric acid, creatine, urea and lactate. The hybrid solgel modified electrode works based on voltammetry method. The electrode comprises a base substrate [20] in the form of a bowl; a screen printed conductor [22] layer in the substrate; characterized by, a hybrid solgel composite [24] layer to cover the conductor [22] and substrate layer, which is sensitive to body analytes by selective voltammetric oxidation of the bio- molecules. The hybrid solgel composite layer comprises tetraethylorthosilicate (TEOS), methyltriethoxysilane, phenyltriethoxysilane, carbon material, and ferrocene compounds [26, 28]. A method to fabricate the composite layer is also described.

BRIEF DESCRIPTION OF DRAWINGS

Fig. 1 is a sectional drawing of the hybrid solgel modified electrode.

Fig. 2 is a drawing showing the structure of ferrocene and ferrocene derivative.

DESCRIPTION OF EMBODIMENTS

Hereinafter, the present invention is described in detail. The invention involves a hybrid solgel modified electrode for detection of analytes in bodily fluid. The sectional drawing of the hybrid solgel modified electrode is shown in Fig. 1 . The hybrid solgel modified electrode comprises a substrate [20] layer, a conductor [24] layer and a hybrid solgel composite [26] layer. The substrate [20] layer, in the form of a bowl, is to provide mechanical strength to the electrode structure and also to give a good adhesion to the screen printed on the conductor layer. The conductor [22] layer is a screen printed conducting layer to provide electrical contact between the hybrid solgel modified electrode and the readout circuitry. The hybrid solgel composite [24] layer, to cover conductor and substrate, is to detect body analytes by selective voltammetric oxidation of the bio-molecules. In a preferred embodiment, the process of fabricating the electrode starts with the substrate [20] base of polymeric material such as FR4 with a typical thickness of 0.5mm, being screen printed on the top with a conductive [24] layer, made of silver paste to form a circular shaped electrode of typically 4mm and wire traces. This conductive paint is then cured in the oven at 120°C for 20 to 60 minutes. Insulating paste such as solder mask is then printed to cover the wire traces and to expose the electrode window.

As for the hybrid solgel composite [26], a preferred embodiment of the composite is prepared with an equal ratio of tetraethylorthosilicate (TEOS), methyltriethoxysilane and phenyltriethoxysilane, mixed with 0.1M of hydrochloric acid in deionized water. The mixture is stirred at room temperature for 4 hours. After that, a carbon material; graphite of 10 weight percent (10 wt%) and ferrocene [26] or ferrocene derivative [28] (1 wt%) are added to the mixture and the resulting composition sonicated for 1 minute. The sonicated composition is then aged for 20 hours or at least 1 hour in capped vial. Usually, the hybrid solgel composite layer comprises the following by-weight ratio: 20% to 40% tetraethylorthosilicate (TEOS);20% to 40% methyltriethoxysilane; 20% to 40% phenyltriethoxysilane; 10% to 35% carbon material; and 1 % to 10% of ferrocene compound.

The structure of ferrocene [26] and ferrocene derivative [28] is shown in Fig. 2. The derivative ferrocene must have at least one substitution at the cyclopentadienyl carbon atom. The carbon material that can be used as one or in combination includes graphite, glassy carbon, carbon nanotubes or diamond. The aged hybrid solgel precursor is then pipetted or dispensed onto the screen printed conductor [22] and substrate layer. The pipetted composition is cured in the oven at 80 °C to 100°C for at least 5 minutes or left at room temperature for at least 1 hour. By then, the hybrid solgel modified electrode is completed. This particular solgel electrode is suitable to be used as a glucose sensor.

Accordingly, the invention disclosed a hybrid solgel modified electrode comprising a substrate [20] layer, a conductor [24] layer and a hybrid solgel composite [26] layer. The hybrid solgel composite is a mixture of tetraethylorthosilicate (TEOS), methyltriethoxysilane and phenyltriethoxysilane, mixed with 0.1 M of hydrochloric acid in deionized water, which is then added with a carbon material and ferrocene [26] or ferrocene derivative. The hybrid solgel modified electrode, which is a non-enzymatic biosensors could then be used to detect analytes based on voltammetry method for biomedical analyses.