Small molecule detection in normal ionic strength buffers

A method of analyzing a solution to assess the presence of an electrically charged molecule in a sample, the method comprising:

• providing the sample to a sensing region of a sample well that comprises two electrode regions, wherein the sample comprises a buffer having an ionic strength in a range between about 10 mM and about 1M;
• contacting the sample with a sensor comprising molecular receptors configured to interact with the electrically charged molecule, wherein the sensor is positioned in the sensing region, wherein the sensor comprises a filament that comprises an optical fiber, wherein an electrode is positioned in each electrode region and is configured to expose the sensor to a frequency-modulated electric field, wherein the sensing region defines a channel between the electrodes, wherein two pieces of electrophoresis gel are positioned in the sample well separately in front of each electrode that cover the electrodes, wherein the two pieces of electrophoresis gel are configured to prevent electrode reaction generated bubbles from entering the sensing region, to maintain solution conductivity, and to reduce a liquid surface area in the sample well, wherein a ratio of a current density at a center of the sensing region to a current density at one of the electrodes is at least 2, wherein a cross section of the sample well perpendicular to a longitudinal axis of the optical fiber has an “H” shape, wherein a center area of the sensing region of the “H” shape sample well comprises a tunnel filled with a solution that connects the two pieces of electrophoresis gel and the electrodes to one another, wherein the sensor is positioned in the center area of the sensing region of the “H” shape sample well, wherein the two pieces of electrophoresis gel are positioned on either side of the center area of the sensing region of the “H” shape sample well, wherein the center area of the sensing region of the “H” shape sample well has a higher current density than areas of the “H” shape sample well that comprise the two pieces of electrophoresis gel when the frequency-modulated electric field is applied perpendicular to the longitudinal axis of the optical fiber, and wherein each of the electrodes comprises a planar shape and each of the electrodes comprises width and height dimensions such that each of the electrodes completely covers a respective side of the “H” shape sample well with the sensing region of the “H” shape sample well disposed between the electrodes;
• applying an alternating electric field perpendicular to the longitudinal axis of the optical fiber;
• assessing an amplitude of the oscillation of the optical fiber using a detector that is configured to detect the amplitude of oscillation of the optical fiber at a frequency of the frequency-modulated electric field and in a direction of a displacement of the sensor;
• and
• based at least in part on the amplitude of the oscillation of the optical fiber, assessing the presence of the electrically charged molecule.