to draw blood, and since flow injection analysis is employed,
the measurement system is complicated and large. Tests can be
performed in a laboratory, but convenient testing at fish farms is
difficult. Development of a needle-type enzyme sensor system
is needed, so a biosensor can be directly inserted into fish to
quantify blood components
In the field of clinical medicine, many needle-type enzyme
sensors have been developed to measure blood glucose [10–15].
Wang and Zhang [14] developed a miniature needle-type
enzyme sensor suitable for the simultaneous amperometric monitoring
of glucose and insulin. The sensor was constructed from
dual modified carbon-paste working electrodes inserted into a
14-gauge needle. Wu et al. [12] reported an enzyme sensor for
whole blood lactate monitoring. The sensor consisted of a stainless
steel needle with surface modified by a polymer material for
enzyme immobilization. Studies of non-invasive glucose sensors
have also been undertaken for application in the field of diabetes
[16–18]. Caduff et al. [17] developed a glucose monitoring system
based on impedance spectroscopy. Changes in the glucose
concentrations can be monitored by varying the frequency in
the radio band over a range, optimized to measure the impact of
glucose on the impedance pattern. However, most sensor systems
are designed for humans or livestock, and such sensors
have rarely been used in fish. For application as fish, sensors
need to be fairly strong, as fish might resist blood collection.
In addition, since testing should be conducted at the fish farm
if possible, portability is an important issue. Moreover, with
many needle-type enzyme sensors, when a sensor is inserted
into a specimen, immobilized enzyme becomes detached when
coming into contact with the specimen surface. The method of
immobilizing enzyme in a narrow needle-type detector is thus
central to the design of a practical needle-type enzyme sensor
The application of fiber optics to the preparation of biosensor
systems has been studied. Several fiber optic biosensors using
fluorescence of ruthenium complexes for the determination of
glucose have been developed [19,20]. The principle of the sensors
is based on the monitoring of oxygen consumption due to
enzymatic reaction of glucose oxidase.
In the present study, to establish a rapid and convenient
method for measuring blood components in fish, a needle-type
enzyme sensor was developed in which an immobilized enzyme
membrane and optic fiber probe using fluorescence of ruthenium
complexes were inserted into a needle-type hollow container to
measure blood glucose levels.