| dc.description.abstract | Creatinine is an important biomarker for evaluating the renal function and its
concentration in serum can be utilized for early detection of kidney disease,
thyroid disorders, and muscular dystrophy. Accurate, reliable, and decentralized
testing of creatinine has become vital owing to the rising trajectory of Chronic
Kidney Disease and its associated risk factors – diabetes and hypertension. The
conventional analytical techniques to estimate serum creatinine are limited by its
non-specificity, prevalent in the optical Jaffe assay, and the high costs, involved
in the enzymatic assays. This has led to intensive research efforts in developing
an accurate, robust, and sensitive sensor for estimating the concentration of
creatinine in serum with cost-effective solutions. This underlies the focus of the
thesis as it primarily discusses various approaches and challenges faced in
developing the intended sensor.
The primary challenge in estimation of serum creatinine is posed by its
reduced concentration in the complex matrix of blood, which is constituted by
varied proteins, whole cells, immunoglobulins, ions, and other metabolites. The
electro-inactivity of creatinine further complicates the measurement by an
electrochemical route. This necessitates selection of a redox probe that has an
inherently high selectivity for creatinine to address both issues. In this thesis, we
have explored non-enzymatic and enzymatic approaches for its detection.
One of the non-enzymatic approaches, involves utilization of a transition
metal – iron that has an affinity for creatinine. The other non-enzymatic approach
involves electrochemical estimation of creatinine by picric acid that is already
utilized in the optical Jaffe reaction. Both the approaches provide reliable
estimation of creatinine in saline and prove the feasibility of estimation of the
reduced concentrations of serum creatinine by non-enzymatic techniques. The
enzymatic approach involves one-step hydrolysis of creatinine by creatinine
deiminase. The resulting N-methylhydantoin is quantified by a highly selective
transition metal-based redox probe – cobalt. This is a novel route for creatinine
estimation that has provided reliable quantification in serum and even, whole
blood. The enzymatic approach assures a higher sensitivity and specificity of
detection in real samples.
Another major issue that limits the clinical use of electrochemical biosensors
for the analytes present in lower concentrations, is electrode fouling caused by the non-electroactive components of the blood. We have investigated different
strategies to minimize this fouling by serum proteins – albumin. The strategies
differ based on the interaction of the redox probe with albumin and are classified
into albumin-reactive and albumin-non-reactive systems. Dilution with
appropriate electrode surface modification has proven effective for albuminreactive
systems. A unique size and charge filter composite has been devised for
albumin-non-reactive systems. This filter composite can be tuned and further
optimized with any disposable electrode platform, based on the required extent
and nature of filtration. It also serves as a viable pre-treatment or activation layer
for the lower cost ultramicroelectrodes.
Decentralized testing necessitates minimal user involvement and no technical
pre-requisites for the measurement. Hence, we have proposed a sequential drop
technique of the sensing chemistry constituting cobalt ions on disposable screenprinted
electrodes as a decentralized testing solution with minimal user
involvement. We have also explored electrodeposition of cobalt ions as an
alternate platform that further minimizes the user involvement by confinement of
the sensing chemistry on the electrode surface.
Thus, this thesis provides a comprehensive exploration of non-enzymatic and
enzymatic techniques for quantification of serum creatinine. The device based on
enzymatic technique has demonstrated success in estimation of creatinine from
whole blood samples of patients with no sample pre-processing, a reduced
turnaround time and high accuracy over a wide dynamic range and has laid the
foundation for the intended point-of-care device. | en_US |
