Joint research project

Luminescent silk nanofibers as platforms for sensing devices (NANOSILK)

Project leaders
Francesco Galeotti, Martin Danko
REPUBBLICA SLOVACCA - SAS - Slovak Academy of Sciences
CNR-SAS 2016-2017
Chemical sciences and materials technology
Thematic area
Chemical sciences and materials technology
Status of the project

Research proposal

Silk fibroin from Bombyx mori cocoon is a promising biomaterial for the development of novel ecosustainable technologies. Its main benefits include optical transparency, outstanding mechanical robustness and compatibility with living systems. For these reasons, potential application of silk in fields such as tissue engineering, drug release systems, implantable electronics, microfluidic devices, optics and photonic systems are currently being investigated by the international research community [H. Tao et al. Adv. Mater.2012, 24, 2824]. In this proposal, with the aim to explore new silk-based sensing and optoelectronic applications, we intend to develop a series of composite materials based on silk fibroin and luminescent perylene diimide (PDI) derivatives. The chemical insertion of aminoacid moieties in perylene structure would be beneficial to impart water-solubility, enabling their homogeneous mixing with silk fibroin in aqueous solution. In addition, the presence of the aminoacidic residues will promote h-bond interaction with fibroin, stabilizing the assembly. PDI-based materials are well-known for their unique spectroscopical and electrochemical properties and their extraordinary chemical, thermal and photostability which allowed their use as prominent chromophores in organic solar cells, field effect transistors, light harvesting arrays and light-emitting diodes. Therefore, their interaction with silk proteins is expected to give rise to novel highly fluorescent composite materials which combine the physical properties of silk with the fluorescence of PDIs. Because these kind of functionalized PDIs tend to aggregate with other molecules or with themselves via π-π stacking, resulting in fluorescence shifting or quenching, they are typically used as probes in aqueous solution, exploiting the optical response to the aggregation-disaggregation process (off-on fluorescence) under external stimuli (other molecules, pH, temperature, etc.). The interaction of PDIs with fibroin matrix could therefore give rise to interesting optical phenomena, exploitable in sensing systems. Different aminoacid-functionalized PDIs will be synthesized by means of a well-assessed and straightforward procedure [Kozma et al. 2015 Dyes Pigm., submitted], and used for the preparation of silk composites at different loading percentages. Then, the materials will be processed into solid silk objects. Films are probably the simplest and most versatile materials from which regenerated silk can be transformed; therefore, silk/PDI mixtures will be initially processed into thin films. The dye doped films will be studied by spectroscopy and x-ray analysis to elucidate the mutual arrangement of silk proteins and dyes. A second way for silk processing we intend to explore in NANOSILK is nanofibers. To this aim, silk solutions loaded with PDI will be electrospun to produce luminescent nanofibers. This is expected to add to the natural occurring self-assembling tendency of silk proteins a further arrangement due to the electrospinning process. Depending on the amount and kind of aminoacid-PDI derivative mixed with fibroin, and consequently on its interaction/arrangement within the silk proteins, differences in the optical behavior are expected. After optimization of the elctrospinning parameters, the dye loaded nanofibers will be tested as platforms for stimuli-responsive fluorescent sensors. Since it is known that silkworm silk show so-called humidity-induced cyclic contraction property, resulting in the expanding and contraction of silks at different humidity levels [I. Agnarsson et al. J. Exp. Biol.2009, 212, 1990], we expect that the exposure of the nanofibers to atmospheric humidity or solvent vapors will affect the nanofiber structure and the fibroin conformation. As a result, the arrangement of the nanoconfined dyes should change, with detectable variation of the fluorescence. The vision of NANOSILK is to investigate the assembly of differently aminoacid-functionalized PDIs inside the silk proteins scaffold, and to explore possibility of employing these composite nanofibers for sensing purposes. CNR-ISMAC/PI-SAS team is highly qualified in the field of the proposal. CNR-ISMAC scientists have extensive experience in perylene functionalization and optical characterization, in silk manipulation, and are gaining experience in the development of sensors and biosensors. PI-SAS scientists have experience in biopolymer manipulation/characterization (including silk fibroin) and in the electrospinning process. The scientists involved in this proposal have already cooperated to the manipulation and patterning of regenerated silk fibroin, to its chemical functionalization, as well as to chemical synthesis in general, which led to significant common scientific results published in international journals; their collaboration in NANOSILK project will help to strengthen their relations. Laboratories are available for chemical synthesis and silk regeneration (CNR-ISMAC and PI-SAS), nanofiber preparation and characterization by optical and electronic microscopy (PI-SAS), x-ray characterization, photophysical studies and optical measurements (CNR-ISMAC).

Research goals

The objectives of NANOSILK are:
o To impart water-solubility and silk protein affinity to perylene dye by chemical functionalization with different aminoacids (Arg, Asp, Met, Cys, Lys, Thr).
o To assess the proper dye concentration range in silk matrix that allows good processability in thin films and nanofibers
o To gain an insight in the arrangement of the dye molecules into the silk proteins scaffold
o To explore different external stimuli (humidity, solvent vapors, pH, temperature, presence of heavy metals in the aqueous solution) and select those which affect more significantly the optical response of the doped nanofibers.
o To propose at least one reliable sensing application for the doped silk nanofibers.

Last update: 27/11/2021