A Comparison of Various Chips Used for the Manufacture of Biosensors Applied in Non-Fluidic Array SPRi, Based on the Example of Determination of Cathepsin D

Abstract

Non-fluidic array SPR imaging (SPRi) with appropriate biosensors is a new tool for the determination of various biomarkers in body fluids. Numerous biomarkers can be determined without signal enhancement or preliminarily preconcentration. The introduction of a new material solution of the chip may increase the scope of the application of this technique. Solutions with adhesive separating foil and an Ag/Au chip were compared with the previously used two-paint separating polymer and pure gold chip. These solutions were tested using the example of a biosensor for cathepsin D (Cath D), which consisted of pepstatin A (a Cath D inhibitor) immobilized via a cysteamine linker using the NHS/EDC protocol. Four material versions of the Cath D biosensor proved adequate in terms of range of linearity, LOQ, precision and recovery. All four versions of the biosensor were used for the determination of Cath D in the blood serum patients with glioblastoma and control samples, producing very similar results and showing an elevated biomarker concentration in the case of cancer. Therefore, the problem of determining the correct level of Cath D in the serum of healthy individuals has been resolved, correcting literature data which ranged over three orders of magnitude.

Keywords: Ag/Au chip; adhesive separating foil; array SPRi; blood serum; cathepsin D; glioblastoma.

Figure 1

Photograph showing chip made from (a) pure gold; (b) Ag/Au covered with adhesive foil and nine measured samples.

Figure 2

Calibration graphs of Cath D biosensors based on: (a) pure gold chips; (b) Ag/Au chips, covered with adhesive foil (circles) or two photopaints (squares). Concentration of pepstatin A: 500 ng mL⁻¹, pH: 3.75.

Figure 3

Linear sections of calibration graphs for the determination of Cath D. Pure gold chips, squares; Ag/Au chips, circles; black points, two paints; open points, adhesive foil. Concentration of pepstatin A: 500 ng mL⁻¹, pH: 3.75.