The paper ‘'Real-time imaging of microparticles and living cells with CMOS nanocapacitor arrays' has been selected for Advance Online Publication (AOP) on Nature Nanotechnology's website. Cecilia Laborde (NanoIonics group),one of the authors, gives an overview of the research in the article below.
We performed proof-of-concept experiments exploiting a new sensing platform with broad potential for biomedical applications. The platform is based on CMOS circuitry, the same technology employed in consumer electronics. Each chip carries an array of about 65,000 nanoelectrodes (gold islands 180 nm in diameter) and their readout electronics distributed in an area far smaller than 1 mm2. Each single electrode acts as an individual sensor by being modulated with an alternating voltage at high frequency and measuring the charge stored during each cycle; the presence of a target molecule in liquid next to an electrode is detected as a change in this charge.
Several electrical sensors already exist that work on related principles. Contrary to our case, however, they typically suffer from the problem that biologically relevant solutions contain a lot of charged ions. These ions move in electric fields, blocking the electric field from a sensing electrode from penetrating into solution. As a result, only particles that are located a few atoms or less from the sensor can be detected, severely decreasing sensitivity. Here we overcome this difficulty by operating the sensor at such high frequencies (50 MHz, i.e. 50.000.000 times per second) that the mobile ions do not have time to react to the applied electrical probe. This is only possible because the whole system (nanoelectrodes and readout electronics) is implanted on the same silicon chip.
We investigated the sensor’s performance by detecting different microspheres under experimental conditions usually unattainable with electrical platforms. We could not only detect the presence of these particles, but we also demonstrated sensitivity to their electrical properties. The experiments were complemented with numerical simulation demonstrating an extremely good agreement between theory and measurements. Finally, we studied the behaviour of several cancer cell lines by ‘filming’ their movement along the sensing area with submicron resolution using only electrical signals.
The research was the result of a collaboration between the MESA+, Wageningen University, the University of Udine and NXP Semiconductors, where the chip was developed. The work at Twente was financially supported by the European Research Council (ERC).
The work was also awarded the 1st poster prize at last Fall’s MESA+ Annual Meeting.
