I have degree in chemical engineering (BSc; METU, Turkey), biotechnology (PhD; Cranfield University, UK) and 10 years professional experience in the area of biosensors. After completing a master’s degree in biochemistry (MSc; GYTE, Turkey), I worked at two Cambridge University spin-off companies (Affinity Sensors and Akubio Ltd.) at different positions. Some of the experiences I obtained during my professional work and PhD study include sensor chip fabrication, sensor surface chemistry development, biological assay development (for the detection of proteins, DNA, virus and bacteria), sensor signal enhancement via nanoparticles and product development from idea to market. Not only did I use different commercial biosensor instruments (optical, piezoelectric and electrochemical) but was also involved in the development of new biosensor devices and sensor chips from prototype to commercial products, and some of the products I developed or was involved in its development are in the market.
Biosensor technology is an exciting area that involves many disciplines. From physics to understand how the instruments work, to the knowledge of immunoassays, protein-protein interaction, DNA hybridisation, viral and bacterial detection, it involves many interesting areas. One of the most valuable contributions of biosensors is that they allow detection of clinically relevant molecules, so they are very important diagnostic tools of our day.
My research interests include:
Molecular recognition, sensing and diagnostics
Nanotechnology application in analytical and life sciences
Genetic and protein biomarker selection and detection
Biosensor assay development and signal enhancement
In most cases biomarker detection tests using label-free biosensors were performed only in buffered pure solutions rather than serum. To obtain clinically relevant results, it is essential to perform the biomarker test in human serum. The main difficulty of using serum as the assay media is high non-specific interaction between the sensor surface and serum proteins. A number of strategies have been employed to reduce the non-specific binding of clinical samples; such as:
use of mixed self-assembled monolayer coatings which contains ethylene glycol units
carboxy methyl dextran surface
addition of additives to assay buffer
use of blocking agents after antibody immobilisation such as milk or certain polymers
use of serum as running buffer to eliminate the mismatch between the running buffer and sample containing serum
diluting the serum till effects of non-specific binding is minimised
The above described methods can either be applied individually or together to reduce the non-specific binding of serum proteins achieving different success. Each one of them has different efficiency and may have some drawbacks. In our study we have designed a new buffer (we call it matrix elimination buffer, in short martix buffer) that eliminates 98% of serum protein non-specific binding and enables assays using high concentrations of human serum. You can find more information from our recent poster displayed at Biosensors 2010 conference in Glasgow:
Y. Uludag, I.E. Tothill, “Development of a Sensitive Detection method for Cancer Biomarkers in Human Serum (75%) using a Quartz Crystal Microbalance Sensor and Nanoparticles amplification system”, Talanta, Vol 82(1), 277-282. PDF
Nucleic acid based recognition of viral sequences can be used together with label-free biosensors to provide rapid, accurate confirmation of viral infection. To enhance detection sensitivity, gold nanoparticles can be employed with mass-sensitive acoustic biosensors (such as a quartz crystal microbalance) by either hybridising nanoparticle-oligonucleotide conjugates to complimentary surface-immobilised ssDNA probes on the sensor, or by using biotin-tagged target oligonucleotides bound to avidin-modified nanoparticles on the sensor. We have evaluated and refined these signal amplification assays for the detection from specific DNA sequences of Herpes Simplex Virus (HSV) type 1 and defined detection limits with a 16.5 MHz fundamental frequency thickness shear mode acoustic biosensor.
Results
In the study the performance of semi-homogeneous and homogeneous assay formats (suited to rapid, single step tests) were evaluated utilising different diameter gold nanoparticles at varying DNA concentrations. Mathematical models were built to understand the effects of mass transport in the flow cell, the binding kinetics of targets to nanoparticles in solution, the packing geometries of targets on the nanoparticle, the packing of nanoparticles on the sensor surface and the effect of surface shear stiffness on the response of the acoustic sensor. This lead to the selection of optimised 15 nm nanoparticles that could be used with a 6 minute total assay time to achieve a limit of detection sensitivity of 5.2 × 10-12 M. Larger diameter nanoparticles gave poorer limits of detection than smaller particles. The limit of detection was three orders of magnitude lower than that observed using a hybridisation assay without nanoparticle signal amplification.
Conclusions
An analytical model was developed to determine optimal nanoparticle diameter, concentration and probe density, which allowed efficient and rapid optimisation of assay parameters. Numerical analysis and subsequent associated experimental data suggests that the response of the mass sensitive biosensor system used in conjunction with captured particles was affected by i) the coupled mass of the particle, ii) the proximal contact area between the particle and the sensor surface and iii) the available capture area on the particle and binding dynamics to this capture area. The latter two effects had more impact on the detection limit of the system than any potential enhancement due to added mass from a larger nanoparticle.
Biosensors 2010 (the most important conference in its area) is organised and sponsored by Elsevier / Biosensors & Bioelectronics with the support of Cranfield University. With 1075 registrations and 66 countries represented, it was truly a world congress.
The topics of the conference included:
Theranostics
Nanobiosensors, nanomaterials & nanoanalytical systems
Lab-on-a-chip
DNA chips & nucleic acid sensors
Immunosensors
Enzyme-based biosensors
Organism- and whole cell-based biosensors
Biofuel and biological fuel cells
Bioelectronics & bionics
Electronic nose technology
Natural & synthetic receptors
Signal transduction technology
Microfluidics & systems integration
Proteomics and single-cell analysis
Commercial developments, manufacturing and markets
Biosensors are analytical devices that comprise a biological recognition element and a suitable transducer, which are usually coupled to an appropriate data processing system (Figure 1) (Lowe, 1985). The biological recognition element may be an enzyme, micro-organism, tissue or bioligand such as antibodies and nucleic acids (Tothill et al., 2001; Tothill and Turner, 2003; Turner, 2007). The transducer converts the physico-chemical change due to the interaction of molecules with the receptor into an output signal. Optical, electrochemical, calorimetric, magnetic, micromechanical and piezoelectric transducers can be employed in biosensors. Recognition elements can be immobilised on sensor support or sensor surface using different methods such as; entrapment, encapsulation, adsorption, capture and covalent attachment.
Figure 1. Schematic of a biosensor.
Biosensors were first described by Clark and Lyon in 1962, who described an amperometric enzyme electrode for glucose (Clark and Lyons, 1962). Shortly after this seminal paper, first glucose, then lactate and alcohol biosensors were commercialized in 1973-1975 by Yellow Springs Instrument (Newman and Turner, 2005). In 1987 a ‘pen style’ glucose sensor was launched by MediSense, which has subsequently become one of the most popular glucose biosensor (Malhotra and Chaubey, 2003). Several other glucose biosensors have been developed since and more than 40 different brands are available on the market now (Newman and Turner, 2005; Wang, 2001). While biosensors for clinical diagnostic measurements of glucose biosensor have been developed and commercialized; generic biosensors for the analysis of different molecular interactions have been developed principally only for research purposes. These types of biosensors employ sensor surface which is ready for the immobilisation of biomolecules of interest for further biomolecular interaction analysis. The main application areas include:
Quality assurance in agriculture, food and pharmaceutical industries
Research and development (proteomics, drug discovery)
Biosensors can be classified according to the recognition element as bioaffinity sensors, enzyme sensors, trans-membrane sensors and whole cell biosensors; or according to the transducer as electrochemical, optical, piezoelectric and calorimetric sensors. Bioaffinity sensors provide real time measurements to detect binding of biomolecules to each other. The antibody antigen (immunosensor) (Gizeli and Lowe, 1996), receptor ligand, DNA and RNA to nucleic acid / protein binding interactions can be detected by means of bioaffinity sensors (Tothill, 2003). While preferred method of detection for catalytic sensors are usually electrochemical, the main method of detection for bioaffinity sensors are generally optical or piezoelectric (Turner, 2000).
Yıldız Uludağ
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A brief introduction to the field of Biosensors including the main types of device, the market size and future perspectives are described by Prof. Anthony Turner, a leading figure in Biosensors area:
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References
Clark, L. C. J., and Lyons, C. (1962). Electrode systems for continuous monitoring in cardiovascular surgery. Ann. NY Acad. Sci. 102, 29-45.
Gizeli, E., and Lowe, C. R. (1996). Immunosensors. Current Opinion in Biotechnology 7, 66-71.
Lowe, C. R. (1985). An introduction to the concepts and technology of biosensors. Biosensors 1, 3-16.
Malhotra, B. D., and Chaubey, A. (2003). Biosensors for clinical diagnostics industry. Sensors and Actuators B: Chemical 91, 117-127.
Newman, J. D., and Turner, A. P. F. (2005). Home blood glucose biosensors: a commercial perspective. Biosensors and Bioelectronics 20, 2435-2453.
Tothill, I. E. (2003). On-line Immunochemical Assays for Food Quality Assurance: Woodhead Publishing Limited.
Tothill, I. E., Piletsky, S., Magan, N., and Turner, A. P. F. (2001). New Biosensors. In Instrumentation and sensors for the food industry, E. Kress-Rogers, and C. J. B. Brimelow (eds): Woodhead Publishing Limited and CRC Press LLC.
Tothill, I. E., and Turner, A. P. F. (2003). Biosensors In Encyclopedia of Food Sciences and Nutrition, B. Caballero, L. Trugo, and P. Finglas (eds): Academic Press.
Turner, A. P. F. (2000). Biosensors – Sense and sensitivity. Science 290, 1315-1317.
Turner, A. P. F. (2007). Biosensors, 5th Edition edition. New Jersey, USA: John Wiley.
Wang, J. (2001). Glucose biosensors: 40 Years of advances and challenges. Electroanalysis 13, 983-988.
