Electrochemical Biosensor for Fluorescein Detection

The experimental material consisted of a screen-printed carbon electrode (SPCE) as a sensing platform, which was purchased from Zensor R&D (Taichung, Taiwan). Figure 1 shows our previous developed biosensor with optimizations to enhance signal detection [17 (link)]. The following materials and reagents were purchased from Sigma-Aldrich (Sigma-Aldrich St. Louis, MO, USA): phosphate-buffered saline (PBS), carboxymethyl dextran sodium salt (CMD-Na), 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC), N-hydroxysulfosuccinimide (NHS), ethanolamine, potassium chloride (KCl), potassium ferricyanide (Fe(CN)₆³⁻), hydrogen peroxide (H₂O₂), 3, 3′, 5, 5′-tetramethylbenzidine (TMB), and diethyl pyrocarbonate (DEPC). NeutrAvidin protein was supplied by Thermo Fisher Scientific (Waltham, MA, USA). Antifluorescein horseradish peroxidase (HRP), a 40,000 dalton protein, was acquired from Abcam (Cambridge, UK). MES-free acid monohydrate, hydroxymethyl-aminomethane (Tris), and ethylenediaminetetraacetic acid (EDTA) were purchased from Amresco (Amresco Inc., Solon, OH, USA). Sodium chloride (NaCl) was obtained from Promega Corporation (Madison, WI, USA). We designed a biotinylated ssDNA probe (bioreceptor probe), fluorescein (FITC) ssDNA probe (detector probe), and artificial mimic targeting sequence using Genomics (Taipei, Taiwan).