Development of a Highly Enantioselective Capacitive Immunosensor for the Detection of α-Amino Acids

Abstract

This work describes a highly enantioselective and sensitive immunosensor for the detection of chiral amino acids based on capacitive measurement. The sensor was prepared by first binding mercaptoacetic acid to the surface of a gold electrode, followed by modification with tyramine utilizing carbodiimide activation. The hapten 4-amino-D-phenylalanine was then covalently immobilized onto the electrode by diazotization. Stereoselective binding of an anti-D-amino acid antibody to the hapten-modified sensor surface resulted in capacitance changes that were detected with high sensitivity by a potentiostatic step method. Using capacitance measurement, detection limits of 5 pg of antibody/mL were attained. The exquisite stereoselectivity of the antibody was also utilized in a competitive setup to quantitatively determine the concentration of the analyte d-phenylalanine in nonracemic samples containing both enantiomers of this amino acid. Trace impurities of d-phenylalanine as low as 0.001% could be detected.

Label‐Free Impedance Biosensors: Opportunities and Challenges

“…Jiang et al used faradaic EIS measurements to validated the simple RC model used for potentiostatic step readout and then used the latter to detect a protein using an antibody capture agent, claiming a detection limit of 10 ng/mL [192]. In an excellent recent paper, Zhang et al detected trace impurities of an enantiomeric drug by tethering the small molecule to be detected as the probe layer, taking advantage of the comparatively large size of the antibody recognition agent (one disadvantage is such a sensor cannot be prepared beforehand) [193]. They demonstrate good reproducibility and low nonspecific response, and report an absolute detection limit of 5 pg/mL as well as detecting a 10 ppm enantiomeric impurity.…”

Chiral Biosensors and Immunosensors

“…Stereoselective binding of an anti-D-amino acid antibody to the haptenmodified sensor surface resulted in capacitance changes that were detected with high sensitivity by a potentiostatic step method enabled to detect impurities of D-phenylalanine as low as 0.001%. The L-enantiomer was not bound by the antibody (Zhang S. et al 2006). Another example of electrochemical sensor is based on the stereoselective interaction of proline with carcinoembrionic antibody (anti-CEA).…”

Stereoselective Interaction between DNA and Stable Chiral Surfaces Modified with 1,2‐Diphenylethylenediamine Enantiomers

“…Firstly, the gold electrodes (1 = 3 mm) were polished successively with 1.0, 0.3 and 0.05 mm alumina, then washed ultrasonically in distilled water and ethanol, drying in the air. Following that, the cleaned electrodes were immediately immersed in 5 mmol L À1 MPA ethanol solution overnight at 4 8C to form a self-assembling monolayer with free carboxyl groups exposed on the gold surfaces [28]. Subsequently, the carboxyl group of the MPA was activated by immersing the electrodes in the EDC and NHS coupling regents for 1.5 h. At last, the electrodes were divided into two groups, one group was immersed in 5 mmol L À1 (1R,2R)-DPEN ethanol solution, another group was in (1S,2S)-DPEN ethanol solution with the same concentration, and were stayed at room temperature for 8 h (they were denoted (1R,2R)-surface or (1S,2S)-surface).…”