Background: The photo thermal lens microscopy is a technique based on measurement of
the temperature rise which is generated in an illuminated matrix because of non-radiative relaxation of
absorbed energy from a laser. It is an ideal system for low detection volume measurements in a micro
channel. Hence, in this study, a combined microfluidic chip-photo thermal lens microscopy (MFCPTLM)
system was assembled for highly sensitive determination of captopril.
Captopril is an angiotensin-converting enzyme (ACE) inhibitor used to treat hypertension, congestive
heart failure and kidney problem caused by diabetes. Captopril had no absorption in visible range but
due to its thiol group, it could interact with Gold nanoparticles (GNPs). So, GNPs act as its labeling
agent and the semi-selective measurement of captopril was achieved.
Methods: A 3.35 nM GNPs and captopril solution by the same flow rate were introduced to the microchannels
by microsyringe pumps. The mixture was detected with an assembled PTLM system.
The applicability of optimized method for determination of captopril in human Serum and pharmaceutical
sample was investigated as well.
Results: The thiol group of captopril bonded to the surface of GNPs, created the core-shell form and
reduced the surface plasmon resonance of GNPs; as a consequence, the PTLM signal of GNPs decreased
following the increase in captopril concentration. The difference between the PTLM signals of
sample and blank was calculated as a ΔPTLM signal.
The detection volume of the PTLM was calculated to be 2.68 fL. At the optimum condition this optical
view comprised of 5.4 GNPs, surrounded by 65-1049 captopril molecules.
Conclusion: In this study, we proposed a sensitive method for the determination of captopril, based on
photo thermal lensing of GNPs in a glass microfluidic chip. The S-type form of microchannel and the
micro space scale of that enhanced the surface interaction of captopril molecules and GNPs and resulted
in more effective reaction.
In addition to the fast interaction time and low detection volume, the main features of this method are
simplicity, good analytical performance, and low reagent consumption in comparison with batch procedures.
The combination of this system with a highly sensitive method such as PTLM reduced the difficulty
of sampling which makes it more attractive.
The results show the capability of the method for sensitive measurement of captopril in human serum
sample and pharmaceutical tablets.