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To address the challenge of accurate, low cost and robust biosensors for diabetes management and early detection of diabetes complications, we have developed novel, robust sensing chemistry (or receptors) for electrochemical POC biosensors. The biosensors have been developed for the bio-markers associated with diabetes management such as glycated haemoglobin (HbA1c), glycated albumin, glucose, biomarkers associated with diabetes complications such as microalbuminuria, urine creatinine and albumin-to-creatinine ratio (ACR) and biomarkers associated with anaemia and malnutrition conditions such as haemoglobin and serum albumin. For haemoglobin detection, a new POC bio sensing technique has been developed based on Aza-heterocyclic chemicals. The repeatability and accuracy of the biosensor have been tested on real pathology samples. The glycated form of haemoglobin, called glycated haemoglobin or HbA1c, is the gold standard test in diabetes management as it gives the 90-days average blood glucose value. We demonstrate a simple method for electrochemical detection of HbA1c by combining bosonic affinity principle along with aza-heterocyclic receptors. The technique has been verified on the real clinical patient samples. Albumin is the most abundant protein in the human blood. Human serum albumin (HSA) is either alone or an associative biomarker in several chronic diseases like necrosis, nephrosis, hepatitis, malnutrition, arthritis, immune disorders, cancer, diabetes and in some severe infections. In pathology laboratories, the serum albumin is usually tested on serum samples and not in whole blood samples. Since albumin is not a metalloproteinase, it is very difficult to develop electrochemical POC biosensor. We have developed a novel technique for the electrochemical detection of serum albumin in whole blood samples, by exploiting its binding property with redox active copper salts. The accuracy of technique has been verified on both real human blood plasma as well as whole blood samples. Glycated albumin, which is the glycated form of serum albumin, is emerging as a novel biomarker for diabetes management, as it gives the average blood glucose value of 15-20 days. It is also extremely useful in chronic kidney disease patients and patients with hemoglobinopathies where HbA1c can give the erroneous results. By combining the copper chemistry along with bosonic affinity principle, we present the first ever demonstration of glycated albumin sensing. Instant blood glucose monitoring is an integral part of diabetes management. Most of the glucometers available in the market are based on glucose oxidase enzyme. We have demonstrated a low cost non-enzymatic electrochemical technique for blood glucose detection using alkaline methylene blue chemistry. The accuracy of the technique has been verified on real human blood plasma samples. Glucometer is one of the most easily available POC biosensor and a useful tool for diabetes population. India has second largest diabetes population in the world. To analyse the accuracy of the POC glucometers which are available in Indian market, a comprehensive study was conducted. The results were compared with clinical accuracy guidelines using exhaustive statistical analysis techniques. The shortcomings of the commercial glucometers are elucidated, regarding different international standards. Diabetic nephropathy is one of the major diabetes complications and is the primary cause of chronic kidney disease (CKD). The presence of albumin in urine is a well-established biomarker for the early detection of diabetic nephropathy. We have developed a technique for electrochemical detection of microalbuminuria for point of care applications by exploring the binding property of human albumin with electrochemically active molecules like copper and hemin. Methylene blue mediated sensing technique has also been proposed. Urine Albumin-to creatinine ratio (ACR) is another variant of the microalbumuria test that can be done any time and does not suffer from the dilution factor of urine. Iron binding property of creatinine is exploited to develop creatinine biosensor, thus enabling POC ACR tests.

Electrochemical techniques have potential for use in conservation, both to evaluate the protectiveness of existing coatings on metal artefacts and to evaluate potential new conservation coatings. Three electrochemical methods have been examined in this study for their applicability to conservation problems. Corrosion Potential Measurement is simple but provides only minimal information on the corrosion processes occurring in an electrochemical system. Electrochemical Impedance Spectroscopy provides both mechanistic and predictive information on coating performance, but the data are complex to interpret and measurements require equipment that is at present too bulky for effective on-site use and beyond the budget of most conservation laboratories. Electrochemical Noise Measurement can be performed using cheap, portable instrumentation and theoretically requires relatively simple statistical processing and interpretation, making it attractive for conservation applications. This project looks at the development of a simple, low cost electrochemical noise measurement system for conservation needs, and uses it to compare Electrochemical Noise Measurement with the other two techniques.

Philosophiae Doctor - PhD / To meet a fast-growing market demand for next generation portable electronic devices with higher performance and increased device functionalities, efficient electrical energy devices with substantially higher energy, power densities and faster recharge times such as supercapacitors are needed. The overall aim of this thesis was to synthesize nanostructured sulphonated polyaniline and transition metal single, binary and ternary mixed oxide doped nanocomposites with electro-conductive properties. These nanocomposites were anchored on activated graphitic carbon and used in design of asymmetric supercapacitors. Tantalum(IV)oxide, tantalum(IV)oxide-nickel(II)oxide, tantalum(II)oxide-manganese(III)oxide, tantalum(II)oxide-nickel(II)oxide-manganese(II,III)oxide nanoparticles were synthesised using modified sol-gel methods. These were then dispersed, individually, in acidic media through sonication and incorporated in-situ into the polymeric matrix during the oxidative chemical polymerization of aniline doped with poly(4-styrene sulphonic acid). These novel polymeric nanocomposites were characterised with FTIR, UV-visible, TEM, SEM, EDS, XRD to ascertain successful polymerization, doping, morphology and entrapment of the metal oxide nanoparticles. SECM approach curves and interrogation of CV revealed that these nanocomposites are conductive and electro-active. The cells showed good supercapacitor characteristics with high specific capacitances of 170.5 Fg⁻¹ in TaO₂- PANi-PSSA, 166.1 Fg⁻¹ in TaO₂-NiO-PANi-PSSA, 248.4 Fg-1 in TaO-Mn₂O₃-PANi- PSSA and 119.6 Fg⁻¹ in TaO-NiO-Mn₃O₄-PANi-PSSA. Their corresponding energy densities were calculated as 245.5 Whg⁻¹, 179.4 Whg⁻¹, 357.7 Whg⁻¹ and 172.3 Whg⁻¹ respectively. They also gave respective power densities of 0.50 Whg⁻¹, 0.61 Whg⁻¹, 0.57 Whg⁻¹ and 0.65 Whg⁻¹ and showed good coulombic efficiencies ranging between 77.97% and 83.19%. These materials are found to have a long cycle life and therefore good electrode materials for constructing supercapacitor cells. / National Research Foundation (NRF)

An effective electrochemical sensor for myoglobin (Myb) detection was developed using a simple procedure of denaturing the protein with guanidine hydrochloride and detecting the released heme group by cyclic voltammetry. The concentration of denaturant was optimized to obtain maximum current response for the analyte (Myb). To improve the sensitivity of the sensor, the working electrode, glassy carbon electrode was modified with a layer of Titania nanotubes (TNT). The direct electrochemical behavior of the modified electrode (TNT-GCE) was studied using cyclic voltammetry (CV). The performance of the sensor was investigated and optimized and the system was evaluated by monitoring the Myb concentration. Despite the reduced current response for the modified electrode compared to bare GCE, the sensitivity of the system was improved significantly by overcoming the large background current due to denaturant. The developed TNT modified electrode improved the detection limit of Myb and showed good stability, sensitivity and reproducibility. Under optimal conditions, the catalytic currents are linearly proportional to the concentrations of Myb in the wide range from 50 nM to 6 M. This approach provides improved sensitivity in the given range, and may provide a novel and efficient platform for the fabrication of sensors for other heme proteins.

Self-assembled monolayers (SAMs) were investigated with regard to their application as templates to control processes down to the nanometre length scale. With applications of SAM for electrochemical nanotechnology in mind, the range of aspects studied comprises patterning on different length scales, behaviour of SAMs under the conditions of electrochemical metal deposition, and the influence of the head and tail groups on formation and structure of SAMs. On a micrometre scale, laser scanning lithography (LSL) was used to pattern SAM covered Au surfaces. With this technique, localized regions of a SAM are desorbed by scanning the focal spot of a laser beam. Thermal desorption occurs as a result of the high substrate temperature produced by the laser pulses. Patterns with line width as small as 0.9 µm were produced by LSL. It is demonstrated that SAM can not only be patterned by laser radiation but can also be rendered more passive as revealed by electrochemical metal deposition. Such blocking effect is explained by annealing of defects upon irradiation at the appropriate laser energy. This effect can block deposition of bulk copper particles, but does not prevent the underpotential deposition. Based on this passivation effect, large passivation areas can be created, which can be used as substrate for further nano/micro fabrication. The combination of SAM patterning and electrochemical metal deposition was also demonstrated to be an effective way to prepare superhydrophobic surfaces, exhibiting a contact angle of 165° (water droplet). Aiming for the generation of smaller structures, scanning tunneling microscopy (STM) is used as a tool to pattern SAMs. Several phenomena observed in STM based manipulation of SAMs are addressed. The first one is sweeping effect. Deposited metal particles on top of SAM and SAMs are swept by STM tip by choosing appropriate I/V parameters. The closer the tip (higher current, lower bias), the more effective it is. Molecularly resolved images confirm that after sweeping, the scanned area is still covered by SAM molecules. This is explained by diffusion. The sweeping process can be repeated, thus, resulting in a layer by layer etching. The second effect is field-induced desorption. Applying a positive voltage (2.5-5V), a SAM is damaged beneath the area of the tip. The damage depends not only on the bias applied, but also on the current setpoint right before applying the bias. The third effect is nanografting. Nanografting was observed that a SAM having a stronger assembling ability can replace the weaker one (matrix layer) in hexadecane solution by STM scanning under normal I/V parameters combination that are usually used for imaging. It is found that longer chain can replace the shorter chain thiol, alkanethiol can replace biphenyl thiol. This method can be applied to pattern SAM. Defects (punched holes) were created purposely on the SAMs covered Au surface and in situ STM was used to investigate the process of Under-Potential Deposition (UPD) and bulk metal deposition. Bulk metal deposition on punched holes depends on the size. Small scale patterning by punching is sufficient for applications based on UPD but not for bulk metal deposition. Several SAMs assembled on Au(111) surface (1-mercaptoundecanoic acid (MUA), Dodecyl Thiocyanate (C12SCN) and bis(pyrazol-1-yl)pyridine-substituted thiol (bpp-SH) and thiocyanate (bpp-SCN)) were investigated with the aim to expand the type of SAMs that can be used as template for further application, such as metal coordination. High quality thiolate monolayers formed by cleavage of the S-CN bond can be obtained on Au(111). Thus, organothiocyanates appear to be a promising alternative to thiols. Well-ordered MUA monolayers are formed in a few hours at the temperature range of 323-363 K by Physical Vapour Deposition (PVD). Self-assembled monolayers of bpp-SH and bpp-SCN on Au(111)/mica were studied with STM. Preparation conditions such as temperature, solvent, and contamination affect the formation of SAMs on Au(111) much more than other common thiols such as alkanethiols and biphenythiols.

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy