Visual detection of the prostate specific antigen via a sandwich immunoassay and by using a superwettable chip coated with pH-responsive silica nanoparticles


A pH-responsive superwettable chip is described whose surface can switch between superhydrophobic and superhydrophilic. It can be used for the visual detection of the prostate specific antigen (PSA) based on contact angle readout. Magnetic beads were modified with primary antibody against PSA. After immunobinding, gold nanoparticles loaded with secondary antibody labeled with glucose oxidase is added. On addition of glucose, gluconic acid is formed which causes a drop in the local pH value. This results in a wettability switch of the pH-responsive superwettable chip from hydrophobic to hydrophilic. Under the optimized conditions, PSA can be quantified with a 3.2 pg mL−1 limit of detection by analyzing the contact angle and the related color that changes from blue via orange to red. The method is applicable to PSA detection in serum samples and for visual classification by cancer patients and healthy persons. It is also suitable for color-blind and color-weak individuals. Conceivably, this kind of assay can be transferred to the determination of various kinds of other bioanalytes including nucleotide, proteins, and even of ions and small organic molecules, and thus is has a wide scope.

Schematic presentation of a pH-responsive superwettable chip coated with silica nanoparticles for the visual detection of prostate specific antigen (PSA) by reading the contact angle. The superwettable chip achieves reliable clinical detection of serum PSA from prostate cancer patients.

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This work was supported by the National Natural Science Foundation of China (31800829, 21703210), the Natural Science Foundation of Shandong Province (ZR2018BB054), and PhD Research Foundation of Linyi University (LYDX2018BS005).

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Correspondence to Ei Ei Sann or Zhong Feng Gao.

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Gao, J.B., Sann, E.E., Wang, X.Y. et al. Visual detection of the prostate specific antigen via a sandwich immunoassay and by using a superwettable chip coated with pH-responsive silica nanoparticles. Microchim Acta 186, 550 (2019).

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  • Contact angle
  • Hydrophilicity and hydrophobicity
  • Cancer patient
  • Magnetic beads
  • Gold nanoparticles