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Functionalization of the plastic chips for selective immobilization of biomolecules is one of the key challenges to be addressed in commercialization of the next-generation point-of-care (POC) diagnostics devices. Multistep liquid-phase deposition process requires a large quantity of solvent to be used in anhydrous conditions, providing quantity of industrial liquid waste. We, in this work, have demonstrated a solventless plasma-based process that integrates low-cost, high throughput, high reproducibility and ecofriendly process for the functionalization of POC device platforms. Amine functionalities have been deposited by plasma-enhanced chemical vapour deposition 2 (PECVD) using a new precursor. For a successful and efficient plasma functionalization process, an understanding of the influence of plasma process parameters on the surface characteristics is essential. The influence of the plasma RF power and the deposition time on the deposited amount of amino functionalities and on their capacity to immobilize nano-objects (i.e., nanoparticles) and biomolecules (i.e. DNA) was examined. Surfacial properties were related to the binding capacity of the films and to the amino content, as revealed by the Ònanoparticle approachÓ and DNA attachment experiments. The key process determinants were to have a sufficient power in the plasma to activate and partially fragment the monomer but not too much as to lose the reactive amine functionality, and sufficient deposition time to develop a reactive layer but not to consume or erode the amine reactivity. An immunoassay performed using human immunoglobulin (IgG) as a model analyte shows an improvement of the detection limit by two orders of magnitude beyond that obtained using devices activated by liquid-phase reaction.

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Even though electrochemical impedance spectroscopy (EIS) has already been used for the in situ electrochemical study of organothiol self-assembled monolayer (SAM) formation on gold, such studies are not available on oxidizable metals. A scrupulous study of SAM formation on oxidizable metals is a challenge, even by ex situ techniques, because of their highly oxidizable nature and their high interaction with the solvent which are irrelevant with the noble metals. In this report, the self-assembling of n-dodecanethiol, n-dodecaneselenol, didodecyl disulfide, and didodecyl diselenide on copper substrate is studied in real time by in situ electrochemical impedance spectroscopy. The interfacial capacitance variation with time was used to study the adsorption process as a function of time. The selfassembling of n-dodecanethiol and n-dodecaneselenol results in the formation of a layer with coverage of around 90% within 10 s. This fast step happens with an effective removal of the surface copper oxide layer. The second stage involves a long-term additional adsorption and consolidation of the SAM. Didodecyl disulfide is incapable for the effective removal of copper oxide layer, and its adsorption is slow and ineffective. Monolayer formation with didodecyl diselenide takes longer time due to slow copper oxide removal. The in situ EIS results were supported by the polarization modulation infrared reflection absorption spectroscopic (PM-IRRAS) studies.

The vibrational response of p-nitrothiophenol (p-NTP) self-assembled monolayers (SAMs), on Pt and on Au, has been investigated by combining theoretical methods with vibrational spectroscopies. Experimentally, the vibrational signatures have been measured using infrared spectroscopy (IR), polarization-modulation reflection absorption infrared spectroscopy (RAIRS), and with sum frequency generation spectroscopy (SFG). Theoretically, density functional theory calculations (DFT) have predicted the molecular vibrations and have estimated their IR vectors and Raman tensors, necessary to simulate the spectra and therefore to interpret the vibrational signatures as well as to retrieve the molecular orientation. So, a tilt angle (ϑ) of 60°for the molecular 1,4-axis of p-NTP has been directly estimated for both Pt and Au SAMs by the polarizationdependent SFG data. Then, combining these results with RAIRS measurements has allowed to determine rotation angles (ξ) of 56°and 66°for p-NTP SAMs on Pt and Au, respectively.

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