Conventionally, an electrical change of a biological sample associated with the activity thereof or the strength of fluorescence emitted by an indicator taken up by a biological sample is captured as a digital signal and measured by a measurement apparatus. For example, the ion channel activity of a cell is measured as follows. In the case of measurement at a single channel level, an electrophysiological measurement apparatus employing a micro-electrode probe (e.g., a patch clamp) and a specialized control apparatus is used to obtain a digital signal (the amount of electricity passing through a channel). From the digital signal, the measurement apparatus calculates the duration, timing, number of times, and the like of opening or closing of the ion channel to determine the activity of the channel (intracellular recording method). In the case of a whole cell, a fluorescence measurement technique is used to determine the amount of ions entering into the cell as a digital signal, and regarded as the ion channel activity of the whole cell.
However, when a captured signal is particularly a digital signal, it is difficult to distinguish a signal of interest from noise signals and therefore it is not possible to detect a change in the activity of a channel associated with the activity of a cell, and the like.
In the patch clamp technique, a micromanipulator requiring a high skill for manipulating is necessary, and it takes much time to measure one sample. Therefore, it is difficult to measure a large number of samples. In the fluorescence measurement technique, a subject to be detected is limited only to ions emitting fluorescence, or when a change in the ion channel activity of a cell is measured in the presence or absence of a chemical substance, such as a drug, or while varying the concentration of the chemical substance, it is necessary to additionally employ a fluorescent material. In this case, unfortunately, the fluorescent material probably has a side effect on a subject and the fluorescence sensitivity of a fluorescent material changes over time.