MESA+ University of Twente
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MESA+ 2016

In this thesis the various ingredients to build a sensing platform for single molecule detection, have been studied. Several practical pitfalls of scaling down such sensors are discussed, and alternate solutions are provided.

‘To this end, we chose electrochemical sensors that are well-suited for miniaturization,’ says Sahana Sarkar. ‘We aimed to develop sensors that can be easily integrated with microelectronics, and which are suited for large-scale microfabrication techniques.’

The PhD work took place within the Mesa+ Nanoionics Group, in close collaboration with industrial partners (Intel and Pacific Biosciences), and the University of Columbia . It was funded by National Institutes of Health (NIH), USA.

‘The detection platform consists of nanofluidic channels,’ Sahana says. ‘It includes a nano-spaced twin electrode system (or: nanogaps), and the detection principle is based on redox cycling. A part of my thesis included the integration of fluid flows within the nanogaps. We completely fabricated the devices here.’

Worldwide, DNA sequencing is a topical research subject, in order to reduce time consuming procedures and to bring down error margins.

‘The aim of the project was to develop fast and low-cost DNA sequencers, for personalised healthcare, to be: reliable, fast, portable and affordable,’ Sahana says. ‘Our approach may be considered a third generation DNA sequencing platform. It can be utilized for a variety of applications, from personalised healthcare to environmental analyses.’

Unconventional electrochemistry

In this thesis, the various ingredients for realizing this kind of electrochemical platforms are discussed. For example several concepts, relevant to researchers while building miniaturized electrochemical platforms, are discussed. These are especially relevant as scaling down such sensors to micro/nano domains often gives rise to nonidealities that are complex and quite challenging to identify.

‘We address the most commonly encountered problems, and their possible alternate solutions,’ Sahana says. Detection within the nanogap sensors without the reference electrodes was explored, both experimentally and theoretically. The principles are seemingly simple, but not very obvious. For example, a novel potentiometric detection method was proposed, for sub nano molar concentrations.

Fluidics

Sahana: ‘We focused on the integration of fluidic control, not only on offering fast methods for exchanging sample solutions within the sensor, but also on minimizing the risks of contamination. Furthermore, we experimented with neurotransmitters - dopamine in particular - within these devices. Fabrication of these sensors also was discussed.’

Multidisciplinary

Sahana enjoyed the multidisciplinary nature of her PhD work, in which she collaborated with the Mesa+ group MNF (Molecular Nanofabrication). ‘The most memorable moment was when the physical, electrochemical and engineering aspects came together in a working fluidics-controlled nanogap integrated device, after two and a half years of work,’ she says.

future

After her PhD project Sahana finds herself confident in working with a variety of cleanroom fabrication techniques. ‘I was free to design and create my own fabrication steps,’ she says. ‘When complications arose, I ran to the technicians to ask for support and help. They were always willing to collaborate and help me out.’

Also experimenting with fluidic devices, Sahana added to her skills. ‘I prefer staying in academics after my PhD Defence,’ she says. ‘I love the freedom of research which I am passionate about. I would like to find a post-doc position. I am very interested in neurotransmitters and their detection methods.’