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Diverse efforts undertaken to mitigate the Debye screening effect of field-effect transistor (FET) biosensors have achieved higher sensitivity. However, the charge transfer or induction mechanism between the captured biomolecules and the sensing surface, resulting in shift of surface potential and, hence, the drain current magnitude, shows poor selectivity for real time detection of ultra-low biomolecule concentration in unamplified samples. Herein, enabling direct interaction of the target molecule with edge passivated thermally reduced graphene oxide, through the template of molecularly imprinted polymer (MIP), specific trap induced characteristic bulges in the noise spectrum has been observed only in the presence of target molecule. Such a phenomenon has not been observed either with antibodies or aptamers as receptors. Hence, the direct interface of MIP with a graphene FET (GFET) results in the generation of an additional electronic label in FET transduction. As a proof of concept, this principle has been validated for serotonin detection in serum in the presence of other neurotransmitters, resulting in detection limit of 0.05 fM in real time, which is more than two orders of magnitude lower than existing reports and, hence, is expected to pave the way for advancing GFET based sensors toward ultrasensitive point-of-care applications without requiring complex machine learning algorithms. [ABSTRACT FROM AUTHOR]

Oxidized porous silicon (PS) is a common topographical biocompatible substrate that potentially provides a distinct in vitro environment for better understanding of in vivo behavior. But in the reported studies on oxidized PS, cell-cell and cell-substrate interactions have been detected only by fluorescent labeling. This paper is the first attempt to investigate real-time sensing of these interactions on HaCaT cells by label-free impedance spectroscopy on oxidized PS of two pore diameters (50 and 500 nm). One of the major requirements for successful impedance spectroscopy measurement is to restrict the channeling of electric field lines through the pores. To satisfy this criterion, we have designed the pore depths after analyzing the penetration of the medium by using computational fluid dynamics simulation. A distributed electrical model was also developed for estimating the various cellular attributes by considering a pseudorandom distribution of pores. It is observed from the impedance measurements and from the model that the proliferation rate increases for 50 nm pores but decreases for 500 nm pores compared to that for planar substrates. The rate of decrease in cell substrate separation (h) in the initial stage is more than the rate of increase in cell-cell junction resistance (Rb) corresponding to the initial adhesion phase of cells. It is observed that Rb and h are higher for 50 nm pores than those for planar substrates, corresponding to the fact that substrates more conducive toward cell adhesion encourage cell-cell interactions than direct cell-substrate interactions. Thus, the impedance spectroscopy coupled with the proposed theoretical framework for PS substrates can sense and quantify the cellular interactions. [ABSTRACT FROM AUTHOR]

We report an electrochemically fabricated silicon oxide nanoporous structure for ultrasensitive detection of AfB1 in food by shift in peak frequency corresponding to maximum sensitivity. It has been observed that the impedance sensitivity changes from 19% to 40% (which is only twice) where as the peak frequency shifts from 500 Hz to 50 kHz, for a change in concentration from 1 fg/ml to 1 pg/ml. This has been attributed to the combined effect of the significant pore narrowing with increasing AfB1 concentration and the opposing nature of impedance change within the nanopores and the conducting substrate immediately below the nanoporous layer. [ABSTRACT FROM AUTHOR]