Vladimir Kitaev

This work overviews recent (last 3–4 years) advances in sensing based on localized surface plasmon resonance (LSPR) of plasmonic metal nanoparticles (PMNPs). Starting with a brief background, recent reviews in the field and relevant related areas are summarized. Next, recent progress in PMNP synthesis and post-synthetic transformations is discussed in the context of PMNP sensing performance. Subsequently, preparation of sensing substrates based on PMNPs is examined. Recent developments in colorimetric and LSPR sensing constitute the core of the review material with the focus on implementation of PMNPs and their sensing modalities. Advances in other sensing methods with direct relevance to PMNP implementations are also highlighted in the context. Perspectives on directions of further advances in LSPR sensing with PMNPs and overcoming existing limitations conclude this review.

This work overviews recent (last 3-4 years) advances in sensing based on localized surface plasmon resonance (LSPR) of plasmonic metal nanoparticles (PMNPs). Starting with a brief background, recent reviews in the field and relevant related areas are summarized. Next, recent progress in PMNP synthesis and post-synthetic transformations is discussed in the context of PMNP sensing utility. Subsequently, preparation of sensing substrates based on PMNPs is examined. Recent developments in colorimetric and LSPR sensing constitute the core of the review material with the focus on implementation of PMNPs and their sensing modalities. Advances in other sensing methods with direct relevance to PMNP implementations are also highlighted in the context. Perspectives on directions of further advances in LSPR sensing with PMNPs and overcoming existing limitations conclude this review.

We present core-satellite assemblies comprising a solid gold nanoparticle as the core and hollow decahedral gold nanoshells as satellites for tuning the optical properties of the plasmonic structure for sensing. The core-satellite assemblies were fabricated on a substrate via the layer-by-layer assembly of nanoparticles linked by DNA. We used finite-difference time-domain simulations to help guide the geometrical design, and characterized the optical properties and morphology of the solid-shell nanoparticle assemblies using darkfield microscopy, single-nanostructure spectroscopy, and scanning electron microscopy. Plasmon coupling yielded resonant peaks at longer wavelengths in the red to near-infrared range for solid-shell assemblies compared with solid–solid nanoparticle assemblies. We examined sensing with the solid-shell assemblies using adenosine triphosphate (ATP) as a model target and ATP-aptamer as the linker. Binding of ATP induced disassembly and led to a decrease in the scattering intensity and a color change from red to green. The new morphology of the core-satellite assembly enabled plasmonic color-coding of multiplexed sensors. We demonstrate this potential by fabricating two types of assemblies using DNA linkers that target different molecules – ATP and a model nucleic acid. Our work expands the capability of chip-based plasmonic nanoparticle assemblies for the analysis of multiple, different types of biomolecules in small sample sizes including the microenvironment and single cells.

Background: Applied nanomaterials in targeted drug delivery have received increased attention due to tangible advantages, including enhanced cell adhesion and internalization, controlled targeted release, convenient detection in the body, enhanced biodegradation, etc. Furthermore, conjugation of the biologically active ingredients with the drug-containing nanocarriers (nanobioconjugates) has realized impressive opportunities in targeted therapy. Among diverse nanostructures, halloysite nanotubes (NHTs) with a rolled multilayer structure offer great possibilities for drug encapsulation and controlled release. The presence of a strong hydrogen bond network between the rolled HNT layers enables the controlled release of the encapsulated drug molecules through the modulation of hydrogen bonding either in acidic conditions or at higher temperatures. The latter can be conveniently achieved through the photothermal effect via the incorporation of plasmonic nanoparticles. Results: The developed nanotherapeutic integrated natural halloysite nanotubes (HNTs) as a carrier; gold nanoparticles (AuNPs) for selective release; docetaxel (DTX) as a cytotoxic anticancer agent; human IgG1 sortilin 2D8-E3 monoclonal antibody (SORT) for selective targeting; and 3-chloropropyltrimethoxysilane as a linker for antibody attachment that also enhances the hydrophobicity of DTX@HNT/Au-SORT and minimizes DTX leaching in body’s internal environment. HNTs efficiently store DTX at room temperature and release it at higher temperatures via disruption of interlayer hydrogen bonding. The role of the physical expansion and disruption of the interlayer hydrogen bonding in HNTs for the controlled DTX release has been studied by dynamic light scattering (DLS), electron microscopy (EM), and differential scanning calorimetry (DSC) at different pH conditions. HNT interlayer bond disruption has been confirmed to take place at a much lower temperature (44 °C) at low pH vs. 88 °C, at neutral pH thus enabling the effective drug release by DTX@HNT/Au-SORT through plasmonic photothermal therapy (PPTT) by light interaction with localized plasmon resonance (LSPR) of AuNPs incorporated into the HNT pores. Conclusions: Selective ovarian tumor targeting was accomplished, demonstrating practical efficiency of the designed nanocomposite therapeutic, DTX@HNT/Au-SORT. The antitumor activity of DTX@HNT/Au-SORT (apoptosis of 90 ± 0.3%) was confirmed by in vitro experiments using a caov-4 (ATCC HTB76) cell line (sortilin expression > 70%) that was successfully targeted by the sortilin 2D8-E3 mAb, tagged on the DTX@HNT/Au. Graphic

A versatile breast cancer‐targeting nanocomposite therapeutic combining docetaxel (DXL), polyvinyl alcohol (PVA) network for controlled release, and silica‐protected magnetic iron oxide nanoparticles (Fe₃O₄ NPs) for targeted delivery and gold nanoparticles (AuNPs) for plasmonic photothermal therapy (PPTT) is presented in this work. First, the designed nanocomposite is magnetically directed for cancer‐targeted therapy confirmed by computerized tomography (CT) scans. Second, 10% DXL by mass is loaded into PVA, a pH and temperature responsive gel, for controlled release. Third, PPTT is confirmed with Au/Fe₃O₄/PVA‐10%DXL using a prototype circulation system and then for tumor treatment in vivo; Au/Fe₃O₄/PVA‐10%DXL is conveniently directed and the entrapped DXL is selectively released (≈96%) via the interaction of green and near‐infrared (NIR) light with the localized surface plasmon resonance of AuNPs. A 75% cell death is reported from in vitro studies with DXL doses as low as 20 µg mL⁻¹ of Au/Fe₃O₄/PVA‐10%DXL, and a 70% tumor growth inhibition is demonstrated by in vivo experiments with the biosafety studies confirming minimal side effects to other organs. Overall, the developed Au/Fe₃O₄/PVA‐10%DXL has a strong potential to simultaneously enhance CT imaging contrast together with the targeted delivery of DXL.

Novel materials for sensing and metallodielectric arrays have been prepared by encapsulation of gold-protected shape-selected silver nanoparticles with a diverse range of shells including iron, manganese, and iridium oxides using a versatile deposition procedure. These shells of varying thickness, porosity, and smoothness encapsulating metal nanoparticles advantageously combine functionalities of plasmonic cores and oxide shells into resulting functional materials. In particular, the size-uniform metal oxide encapsulated metal nanoparticles (MO-MNPs) assemble into well-ordered metallodielectric arrays for plasmonic applications. The shape and the localized surface plasmon resonance (LSPR) of the metal cores are well preserved, while the chemical and colloidal stability is enhanced by the formation of oxide shells. Metal oxide shells impart the selectivity of detection in surface enhanced Raman spectroscopy (SERS) and surface plasmon resonance (SPR) sensing. Notably, selective sub-mM SPR detection of phosphate ions has been demonstrated.

Efficient and facile preparation of gold nanostructures (AuNSs) with tunable size and localized surface plasmon resonance, LSPR, is accomplished using the developed versatile water‐soluble gold thiolate precursor Au(I)glutathione (Au(I)GSH). Optimal AuNS tuning is achieved via photochemical pathway. The LSPR of AuNSs can be tuned from 518 to 750 nm by using different light‐emitting diode (LED) wavelengths and through size and shape (compact versus multipods) variation. Furthermore, suitability of the developed precursor is demonstrated in the thermal pathway and seed‐mediated regrowth to fine‐tune AuNSs. Overall, diverse tunable AuNSs can be conveniently prepared through several pathways by transformations of the developed thiolate precursor to suit diverse functional applications.

Stability and precise control over functional properties of metal nanoparticles remain a challenge for the realization of prospective applications. Our described process of shell formation and rebuilding can address both these challenges. Template silver nanoparticles (AgNPs) stabilized by poly(styrenesulfonate) are first transformed with gold deposition, after which the resulting shell rebuilds with the replaced silver. The shell formation and rebuilding are accompanied by large shifts in localized surface plasmon resonance (LSPR) peak position, which enables LSPR tuning in a range from 470 to 800 nm. Furthermore, chemical stability of Au–AgNPs is significantly improved compared to AgNPs due to gold stability. Silver templates of different shapes and sizes were demonstrated to transform to AuAg composite NPs to further extend the accessible LSPR range tuning. Stabilization of template AgNPs with poly(styrenesulfonate), in contrast to commonly used poly(vinylpyrrolidone), was found to be a key factor for shell rebuilding. The developed Au–AgNPs were shown to be advantageous for surface plasmon resonance (SPR) detection and surface-enhanced Raman spectroscopy (SERS) owing to their tunable LSPR and enhanced stability.