The antigen-antibody reaction of human choriogenadotropin has been potentiometrically investigated by use of a cyanogen bromide-treated electrode coated with the corresponding anti-serum. The potential of the modified electrode shifts in the positive direction upon contact with a solution of choriogonadotropin. The rate of the reaction at the interface between the electrode and the solution is estimated from the potentiometric measurement to be of the order of 10(4) mol-1 s-1 in diethyl barbiturate buffer, depending to some extent on the rotation speed of the stirrer. The change in potential is almost proportional to choriogonadotropin concentration. It is also pH dependent, the maximum response being at pH 8.7. The technique, applied to samples of human urine, has shown a specific response to choriogonadotropin.

Titanium electrode surface was chemically modified with an aminosilane. The potential of the electrode was shifted to the negative direction by a reaction of fluorescein isothiocyanate in solution with the amine on the electrode surface. The absorption and emission spectra were measured for the fluorescein isothiocyanate, fixed by the reaction with the aminosilane which was chemically bound on the surfaces of tin oxide, titanium oxide and quartz, in solutions and in air. In an alkaline solution, the absorption and emission spectra showed the band ascribable to the dianion of the fluorescein. A peak, attributable to the monoanion, was observed in both absorption and emission spectra measured for the samples kept in air. The surface coverage of the dye was estimated from the absorbances to be about 10−6 mol m−2 for both tin oxide and quartz. The bound dye fluoresced under exposure to ultraviolet light, due probably to the energy transfer from tin oxide to the dye.

The potential of a titanium metal electrode modified with trypsin changes as a result of the complex formation reaction between trypsin and its inhibitor, aprotinin, dissolved in the solution. A similar potential change in the opposite direction occurs by the reaction between aprotinin-modified electrode and trypsin in the solution. The induced changes in both cases depend on the pH of the solution, showing the maximum change at pH = 9.5. The potentiometric response of the trypsin-modified electrode for the consecutive addition of aprotinin and proflavine proves that trypsin bound on the solid surfaces reacts with aprotinin much more strongly than with proflavine. This result is fully consistent with the spectroscopically observed behavior of a trypsin-modified quartz plate against these inhibitors. The surface coverage of trypsin on the quartz plate is also determined by a near-ultraviolet absorption measurement.