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Topics in Current Chemistry (2020) 378:8
carrier [16, 17], contrast agents in X-ray imaging and computed tomography for cancer diagnosis [18, 19], to name only a few. AgNPs display an inherent antimicrobial
capacity against bacteria, viruses, and other eukaryotic microorganisms [20, 21].
Indeed, silver compounds have been used historically to prevent microbial growth in
many fields, such as in wound care and in products such as odor-reducing clothing,
acne creams, and face masks [22, 23].
Topical administration of compounds presents several advantages compared with
other routes such as oral, nasal, and intravenous administration. Transdermal delivery overcomes first-pass hepatic metabolism and can reduce harmful side-effects
[24–26]. However, skin is a complex multilayer structure (composed mainly of epidermis, dermis, and hypodermis) and is a highly impermeable barrier to most molecules on the basis of particle size, water-solubility and surface charge [24]. In addition, hair follicles have also been explored as a more permeable transport channel
for transdermal drug delivery [27–29]. An excellent review of the influence of size
on the penetration of both metal and non-metal NPs through skin was published by
Larese Filon et al. [30].
Naked NPs do not overcome skin barriers efficiently, as reported by NúñezLozano et al. [31] In other words, non-functionalized NPs constitute poor transdermal drug delivery systems [32, 33]. Therefore, many efforts have been made to
enhance the skin penetration of NPs through purposely designed chemical functionalization with biomolecules and bioinspired polymers to form biomimetic NPs
providing additional abilities in skin penetration. Herein, the latest advances in the
development of different approaches to fabricate bioconjugated plasmonic NPs for
enhanced skin penetration are presented. This review is organized as follows: first,
the influence on the skin penetration of key parameters of non-bioconjugated plasmonic NPs is discussed, and, second, some of the more recently reported bioconjugated plasmonic NPs for enhanced skin penetration are presented.
2 Influence of Key‑Parameters on the Skin Penetration
of Non‑bioconjugated Plasmonic NPs
The ability of plasmonic NPs to penetrate skin can be tuned by controlling their
core-composition, particle-size and -shape, surface charge, water solubility and
functionalization strategy, including both capping-ligands and delivered cargoes,
i.e., drugs, genes, and proteins. Relevant examples of the most prominent studies in
each of these parameters are mentioned below.
2.1 Core Composition (Noble Metal Type)
The literature indicates a significant difference in terms of skin penetration behavior between organic and inorganics NPs. There are also significant differences in
skin internalization depending on the chemical composition (i.e. TiO 2 , SiO 2 , ZnO,
FeO, CdSe, Pd, etc.) within the latter group, as previously reported by Larese Filon
et al. [30]. In the case of plasmonic NPs, in vitro penetration of AgNPs through
221
Reprinted from the journal
Topics in Current Chemistry (2020) 378:8
carrier [16, 17], contrast agents in X-ray imaging and computed tomography for cancer diagnosis [18, 19], to name only a few. AgNPs display an inherent antimicrobial
capacity against bacteria, viruses, and other eukaryotic microorganisms [20, 21].
Indeed, silver compounds have been used historically to prevent microbial growth in
many fields, such as in wound care and in products such as odor-reducing clothing,
acne creams, and face masks [22, 23].
Topical administration of compounds presents several advantages compared with
other routes such as oral, nasal, and intravenous administration. Transdermal delivery overcomes first-pass hepatic metabolism and can reduce harmful side-effects
[24–26]. However, skin is a complex multilayer structure (composed mainly of epidermis, dermis, and hypodermis) and is a highly impermeable barrier to most molecules on the basis of particle size, water-solubility and surface charge [24]. In addition, hair follicles have also been explored as a more permeable transport channel
for transdermal drug delivery [27–29]. An excellent review of the influence of size
on the penetration of both metal and non-metal NPs through skin was published by
Larese Filon et al. [30].
Naked NPs do not overcome skin barriers efficiently, as reported by NúñezLozano et al. [31] In other words, non-functionalized NPs constitute poor transdermal drug delivery systems [32, 33]. Therefore, many efforts have been made to
enhance the skin penetration of NPs through purposely designed chemical functionalization with biomolecules and bioinspired polymers to form biomimetic NPs
providing additional abilities in skin penetration. Herein, the latest advances in the
development of different approaches to fabricate bioconjugated plasmonic NPs for
enhanced skin penetration are presented. This review is organized as follows: first,
the influence on the skin penetration of key parameters of non-bioconjugated plasmonic NPs is discussed, and, second, some of the more recently reported bioconjugated plasmonic NPs for enhanced skin penetration are presented.
2 Influence of Key‑Parameters on the Skin Penetration
of Non‑bioconjugated Plasmonic NPs
The ability of plasmonic NPs to penetrate skin can be tuned by controlling their
core-composition, particle-size and -shape, surface charge, water solubility and
functionalization strategy, including both capping-ligands and delivered cargoes,
i.e., drugs, genes, and proteins. Relevant examples of the most prominent studies in
each of these parameters are mentioned below.
2.1 Core Composition (Noble Metal Type)
The literature indicates a significant difference in terms of skin penetration behavior between organic and inorganics NPs. There are also significant differences in
skin internalization depending on the chemical composition (i.e. TiO 2 , SiO 2 , ZnO,
FeO, CdSe, Pd, etc.) within the latter group, as previously reported by Larese Filon
et al. [30]. In the case of plasmonic NPs, in vitro penetration of AgNPs through
221
Reprinted from the journal