Layer-by-Layer Technique as a New Approach to Produce Nanostructured Films Containing Phospholipids as Transducers in Sensing Applications

Abstract

Phospholipids are widely used as mimetic systems to exploit interactions involving biological membranes and pharmacological drugs. In this work, the layer-by-layer (LbL) technique was used as a new approach to produce multilayered thin films containing biological phospholipids applied as transducers onto Pt interdigitated electrodes forming sensing units of an electronic tongue system. Low concentrations (nM level) of a phenothiazine compound were detected through impedance spectroscopy. Both negative 1,2-dipalmitoyl-sn-3-glycero-[phosphor-rac-(1-glycerol)] (DPPG) and zwitterionic l-alpha-1,2-dipalmitoyl-sn-3-glycero-phosphatidylcholine (DPPC) phospholipids were used to produce the LbL films, whose molecular architecture was monitored combining spectroscopy and microscopy at micro and nanoscales. The sensor array was complemented by Langmuir-Blodgett (LB) monolayers of DPPG and DPPC deposited onto Pt interdigitated electrodes as well. It was found that the distinct molecular architecture presented by both LbL and LB films plays a key role on the sensitivity of the sensor array with the importance of the LbL films being demonstrated by principal component analysis (PCA).

On the distinct molecular architectures of dipping- and spray-LbL films containing lipid vesicles

“…Therefore, electrostatic interactions between CH 3 -N + (DODAB) and PO 4 − (DPPG) groups appear not to be the main driving force to grow DODAB/DPPG dippingand spray-LbL films. This is in contrast to the results for PAH/DPPG LbL films [38], where stronger interactions between DPPG and PAH leading to larger FTIR spectral changes were found for dipping-LbL films than for the spray-LbL films. For DODAB/DPPG, a shoulder at 1717 cm −1 was observed only for the spray-LbL film, and may be assigned to hydrogen bonds between COO ester groups and glycerol OH groups of adjacent DPPG molecules, according to Dicko et al [45] who reported a shoulder at 1720 cm −1 in the spectrum of a DPPG Langmuir monolayer using polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS).…”

“…200 nm and 100 nm for dipping-and spray-LbL films, respectively. We concluded that most vesicles were preserved based not only on these AFM images but also on previous evidence from the literature that the vesicles maintain their internal aqueous phase in LbL films [38,52]. Some of the vesicles may nevertheless have been either fused or destroyed by the spraying pressure, as less vesicles are found in the spray-LbL film.…”

“…The DODAB/DPPG dipping-LbL films were grown upon adapting the experimental procedure reported in [38]. The substrate was immersed into distinct solutions according to the following sequence: DODAB dispersion (3 min) → ultrapure water gently stirred to remove non-adsorbed DODAB (1 min) → DPPG dispersion (3 min) → ultrapure water to remove non-adsorbed DPPG (1 min).…”

“…In case of zwitterionic phospholipid, the growth of PAH/DPPC dipping-LbL film is limited to 13 bilayers. [38] Spray-LbL films containing multilayers of PAH(+)/DPPG(−), DODAB(+)/DPPG(−), PAH(+)/DPPC (zwiterionic) or PAH(+)/DODAB(+) were successfully grown, as displayed in Fig. S3a.…”

Vibrational spectroscopy for probing molecular-level interactions in organic films mimicking biointerfaces

“…Of particular relevance is the molecular-level interaction between components which may lead to completely distinctive properties of the final film in comparison to those of the individual components. For instance, Aoki et al [166] immobilized DPPG vesicles onto PAH layers using the LbL technique. FTIR spectroscopy revealed that the interactions between NH 3 + (PAH) and PO 4 − (DPPG) groups are the main driving forces for the PAH/DPPG LbL film growth.…”