Boon Chong Cheah

An Integrated Circuit for Chip-Based Analysis of Enzyme Kinetics and Metabolite Quantification

We have created a novel chip-based diagnostic tools based upon quantification of metabolites using enzymes specific for their chemical conversion. Using this device we show for the first time that a solid-state circuit can be used to measure enzyme kinetics and calculate the Michaelis-Menten constant. Substrate concentration dependency of enzyme reaction rates is central to this aim. Ion-sensitive field effect transistors (ISFET) are excellent transducers for biosensing applications that are reliant upon enzyme assays, especially since they can be fabricated using mainstream microelectronics technology to ensure low unit cost, mass-manufacture, scaling to make many sensors and straightforward miniaturisation for use in point-of-care devices. Here, we describe an integrated ISFET array comprising 216 sensors. The device was fabricated with a complementary metal oxide semiconductor (CMOS) process. Unlike traditional CMOS ISFET sensors that use the Si3N4 passivation of the foundry for ion detection, the device reported here was processed with a layer of Ta2O5 that increased the detection sensitivity to 45 mV/pH unit at the sensor readout. The drift was reduced to 0.8 mV/hour with a linear pH response between pH 2-12. A high-speed instrumentation system capable of acquiring nearly 500 fps was developed to stream out the data. The device was then used to measure glucose concentration through the activity of hexokinase in the range of 0.05 mM-231 mM, encompassing glucoses physiological range in blood. Localised and temporal enzyme kinetics of hexokinase was studied in detail. These results present a roadmap towards a viable personal metabolome machine.

A

There is a requirement for an electrochemical sensor technology capable of making multivariate measurements in environmental, healthcare, and manufacturing applications. Here, we present a new device that is highly parallelized with an excellent bandwidth. For the first time, electrochemical cross-talk for a chip-based sensor is defined and characterized. The new CMOS electrochemical sensor chip is capable of simultaneously taking multiple, independent electroanalytical measurements. The chip is structured as an electrochemical cell microarray, comprised of a microelectrode array connected to embedded self-contained potentiostats. Speed and sensitivity are essential in dynamic variable electrochemical systems. Owing to the parallel function of the system, rapid data collection is possible while maintaining an appropriately low-scan rate. By performing multiple, simultaneous cyclic voltammetry scans in each of the electrochemical cells on the chip surface, we are able to show (with a cell-to-cell pitch of 456

16\times16

\mu \text{m}

CMOS Amperometric Microelectrode Array for Simultaneous Electrochemical Measurements

) that the signal cross-talk is only 12% between nearest neighbors in a ferrocene rich solution. The system opens up the possibility to use multiple independently controlled electrochemical sensors on a single chip for applications in DNA sensing, medical diagnostics, environmental sensing, the food industry, neuronal sensing, and drug discovery.

Hybrid Dual Mode Sensor for Simultaneous Detection of Two Serum Metabolites

Metabolites are the ultimate readout of disease phenotype that plays a significant role in the study of human disease. Multiple metabolites sometimes serve as biomarkers for a single metabolic disease. Therefore, simultaneous detection and analysis of those metabolites facilitate early diagnostics of the disease. Conventional approaches to detect and quantify metabolites include mass spectrometry and nuclear magnetic resonance that require bulky and expensive equipment. Here, we present a disposable sensing platform that is based on complementary metal–oxide–semiconductor process. It contains two sensors: an ion sensitive field-effect transistor and photodiode that can work independently for detection of pH and color change produced during the metabolite-enzyme reaction. Serum glucose and cholesterol have been detected and quantified simultaneously with the new platform, which shows good sensitivity within the physiological range. Low cost and easy manipulation make our device a prime candidate for personal metabolome sensing diagnostics.

Wide-range optical CMOS-based diagnostics

Colorimetric, chemiluminescence and refractive index based diagnostics are some of the most important sensing techniques in biomedical science and clinical medicine. Conventionally laboratories and medical clinics rely on bulky and dedicated equipment for each diagnostic technique independently. In this paper, we present CMOS sensor based solutions, comprising a single photon avalanche detector array and photodiode array. The CMOS platform offers low cost integration and wide range of light-based diagnostic techniques, leading to development of point-of-care devices.

Metabolomics on CMOS for personalised medicine

The emergence of personalised and precision healthcare requires detailed knowledge of human molecular pathology. Genomics has been transformed by sequencing technologies that can unravel the human genome in 1 day for less than a thousand dollars. Recently, metabolomics, the quantitative measurement of small molecules, has emerged as a field to study an individual’s molecular profile. This is very important because a genome can only give a prediction of an individual’s propensity to a disease – genotyping, while a metabolome can provide immediate diagnosis of biochemical activity in human body – phenotyping. However, the present approach of measuring metabolites depends on large and expensive equipment such as NMR spectroscopy and mass spectroscopy. More importantly, this equipment does not provide a single analytical platform to measure the entire metabolome. CMOS technology has made a major impact in personal mobile computing, digital imaging and communications as part of everyday life. CMOS provides a single integrated platform for sensing technologies, low-cost manufacturing and miniaturisation of microelectronic systems. CMOS has been used successfully to create an all-electronic sequencing technology. We anticipate that CMOS has the potential to allow multiple biomarkers to be monitored in parallel, thus paving the way for metabolome profiling. This review will provide a background to personalised medicine, in terms of genomics and metabolomics, to show the importance for future healthcare delivery. A theoretical background of enzymes for metabolite quantification will also be discussed. A description of DNA microarray technologies will be provided. A background of CMOS chemical sensor systems will be presented for DNA sequencing and metabolite quantification. Finally, a discussion of future CMOS sensor systems, microelectronics and integration technologies that could lead to new “omics” technologies, will be given.

An integrated portable system for single chip simultaneous measurement of multiple disease associated metabolites

Metabolites, the small molecules that underpin life, can act as indicators of the physiological state of the body when their abundance varies, offering routes to diagnosis of many diseases. The ability to assay for multiple metabolites simultaneously will underpin a new generation of precision diagnostic tools. Here, we report the development of a handheld device based on complementary metal oxide semiconductor (CMOS) technology with multiple isolated micro-well reaction zones and integrated optical sensing allowing simultaneous enzyme-based assays of multiple metabolites (choline, xanthine, sarcosine and cholesterol) associated with multiple diseases. These metabolites were measured in clinically relevant concentration range with minimum concentrations measured: 25 μM for choline, 100 μM for xanthine, 1.25 μM for sarcosine and 50 μM for cholesterol. Linking the device to an Android-based user interface allows for quantification of metabolites in serum and urine within 2 min of applying samples to the device. The quantitative performance of the device was validated by comparison to accredited tests for cholesterol and glucose.

Immunoassay Multiplexing on a Complementary Metal Oxide Semiconductor Photodiode Array

Scalable immunoassay multiplexing offers a route to creating rapid point-of-care (POC) diagnostics. We present a method for multiplexing immunoassays on the surface of a complementary metal oxide semiconductor (CMOS) sensor array integrated circuit (IC) without the use of physical separators such as wells or channels. Major advantages of using a CMOS sensor array include low mass-manufacturing costs, the possibility to multiplex multiple assays on a single IC, and improved signal when averaging multiple sensors, along with providing a platform where wash steps can be incorporated to maximize selectivity and sensitivity compared to paper based lateral flow immunoassay. The device was able to differentiate between samples containing either, neither, or both rabbit anti-mouse (RAM) antibodies and/or anti-HIV gp120 antibodies in serum using a gold-nanoparticle promoted silver enhancement immunoassay. HIV antibody concentrations down to 100 μg/mL were readily detected, which is three times lower than those typically found in infected humans (300–500 μg/mL), and the limit of detection was 10 μg/mL.

Hybrid amperometric and potentiometrie sensing based on a CMOS ISFET array

Potentiometry and amperometry are some of the most important techniques for electroanalytical applications. Integrating these two techniques on a single chip using CMOS technology paves the way for more analysis and measurement of chemical solutions. In this paper, we describe the integration of electrode transducers (amperometry) on an ion imager based on an ISFET array (potentiometry). In particular, this integration enables the spatial representation of the potential distribution of active electrodes in a chemical solution under investigation.