Thin film cells early developments

At the early stage of the development of the heart-on-a-chip, a PDMS microfluidic network was combined with planar electrode array to measure the extracellular potential from individual adult cardiomyocytes [54]. Another microfluidic device with an array of electrodes was developed to electrically measure the metabolic profile of cardiomyocytes and optically measure cell contractility [55]. Grosberg et al. first introduced a tissue level heart-on-a-chip to measure the contractility of neonatal cardiac muscle tissue [52]. In the design, eight muscular thin films (MTF) were fabricated on a chip. A layer of poly(N-isopropylacrylamide) (PIPAAm) dissolved at below 35 °C is spin-coated on top of a glass slide (Fig. 5A). Subsequently, a PDMS layer was coated on top of the PIPAAM layer. The PDMS layer was used to seed neonatal rat ventricular cardiomyocytes. The substrate seeded with cells is placed in the bath and the film layers were manually cut to fabricate an array of two opposite rows of four rectangular film layers of MTFs. The MTFs are peeled off after PIPAAm is dissolved as a solution when kept below 35 °C. Finally, electrodes are placed on the top and the bottom of MTFs. 

Cells exploit bilayer structures to create anatomical boimdaries, eg in the case of cell membranes which are composed of lipids, proteins, and carbohydrates. During the early 1960s researchers demonstrated that certain classes of lipids, especially phospholipids, could be used to form protein- and carbohydrate-free model membranes. Methods were developed for the preparation of supported bilayer lipid membranes (1), and it was discovered that dried thin films of phospholipids spontaneously hydrate to yield lipid vesicles (2). Vesicles have since then been used as model systems for fluid interfaces and biomembranes (3). Practical applications involving vesicles are in the area of cosmetics and pharmaceutics. 

A polymer film (nominally of micrometer thickness) on the electrode surface can be considered to be a solid-state electrochemical analog of the thin-layer cell. Thus, electrochemical processes within the polymer film can be modeled similarly to their thin-layer solution counterparts (with some important distinctions as discussed in Section I earlier and in what follows). Indeed, many of the theoretical developments in the electrochemistry of polymer-modified electrode surfaces were inspired by the earlier developments (in the 1960s and early 1970s) in thin-layer electrochemistry. 

Early bolometers used, as thermometers, thermopiles, based on the thermoelectric effect (see Section 9.4) or Golay cells in which the heat absorbed in a thin metal film is transferred to a small volume of gas the resulting pressure increase moves a mirror in an optical amplifier. A historical review of the development of radiation detectors until 1994 can be found in ref. [59,60], The modern history of infrared bolometers starts with the introduction of the carbon resistor, as both bolometer sensor and absorber, by Boyle and Rogers [12], The device had a number of advantages over the Golay cell such as low cost, simplicity and relatively low heat capacity at low temperatures. 

An early example of an MIP-QCM sensor was a glucose monitoring system by Malitesta et al. (1999). A glucose imprinted poly(o-phenylenediamine) polymer was electrosynthesized on the sensor surface. This QCM sensor showed selectivity for glucose over other compounds such as ascorbic acid, paracetamol, cysteine, and fructose at physiologically relevant millimolar concentrations. A unique QCM sensor for detection of yeast was reported by Dickert and coworkers (Dickert et al. 2001 Dickert and Hayden 2002). Yeast cells were imprinted in a sol-gel matrix on the surface of the transducer. The MIP-coated sensor was able to measure yeast cell concentrations in situ and in complex media. A QCM sensor coated with a thin permeable MIP film was developed for the determination of L-menthol in the liquid phase (Percival et al. 2001). The MIP-QCM sensor displayed good selectivity and good sensitivity with a detection limit of 200 ppb (Fig. 15.7). The sensor also displayed excellent enantioselectivity and was able to easily differentiate the l- and D-enantiomers of menthol. 

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