A novel biosensor based on Blu-ray disc coating film for determination of total amino acid content in tea leaves

Abstract

Biosensor substrate materials are a key research focus in the field of sensors. Blu-ray discs (BDs) as universal sensor substrates are advantageous in comparison with other substrates (conventional paper and polycarbonate) in terms of easier activity treatment and higher density of reactive groups on the film surface. In this study, a novel and simple microfluidic biosensor based on BD coating film was developed by treating with sodium hydroxide solution and a piece of filter paper at slightly elevated temperatures. There are no significant physical damages to the substrate morphology, and the aging effect is minimal. The unique wetting, optical, and self-cleaning properties of the modified surfaces can be demonstrated in the paper. We have tested this new type of biosensor substrates for assay applications (the determination of total amino acids in tea leaves), which showed excellent performance in terms of sensitivity and reproducibility. The novel biosensor substrate material based on a simple BD coating film displayed preferable merits with easy making, low cost, easy using, and extensive application prospect.

Fig. 1. Creation demonstration of assay region in the microfluidic sensor.

Fig. 2. Side-view images of water droplets on BD coating film: (A) untreated film, and (B) film treated with 1.0 M NaOH aqueous solution for 1 h at 55 °C. The dashed horizontal lines indicate the contact lines between the water droplet and the BD film surface; the portion above the line is the water droplet and the portion below the line is a reflection of the droplet. The contact angles, measured by an AST VCA system, are (A) 141 ± 3° and (B) 36 ± 2°.

Fig. 3. Schematic diagram of fabricating patterning by wet etching. (a) Native filter paper, (b) paper mask produced by cutting on the filter paper, (c) paper mask penetrated with NaOH solution, (d) NaOH paper mask on BD surface, (f) remove paper masker, and (g) patterning with hydrophilic–hydrophobic contrast.

Fig. 4. Dependence of water contact angle at the BD-R film surface on activation time during the treatment with 1.0 M NaOH at 55 °C (solid circles) and an untreated BD surface (open circles). The experimental uncertainties were determined from at least three sets of independent measurements.

Fig. 5. BD-R surface on storage time (aging) after initial activation by dependence of water contact angle at the BD-R film surface on storage time (aging) after initial activation by NaOH solution (1.0 M) for 45 min at 55 °C. The dashed and solid lines are to direct the eyes only. The experimental uncertainties were determined from three sets of independent measurement.

Fig. 6. Contact angles of buffer solutions on a BD-R film surface treated with 1.0 M NaOH for 45 min at 55 °C (solid circles) and an untreated BD surface (open circles). Each data point represents the average reading of at least three replicated data, and the error bars show the corresponding standard deviation.

Fig. 7. AFM images and corresponding cross sections of the BD-R surfaces (a) before and (b) after hydrolyzation with NaOH solution (1.0 M) for 45 min at 55 °C.

Fig. 8. (A) Images showing the results of amino acid assay on the simple microfluidic sensor based on BD coating film with varied concentrations. (B) Mean grayscale intensity value varies as a function of isoleucine concentration obtained from data of (A). The grayscale intensity values were provided by the Adobe Photoshop CS4 software after subtraction of the blank value.