Monomer adsorption of indocyanine green to gold nanoparticles

Thiolated Cyanines Appended to Partially Pegylated Gold Nanoparticles for Fluorescence Quenching of Two-Channel Photothermal Inks

Following a new approach, we prepared a nanoink with two separate photothermally responsive absorption bands. One is the localized surface plasmon resonance (LSPR) absorption of gold nanoparticles (AuNP, d=17 nm), the second is the absorption band of two cyanine (Cy) dyes, Cy7-C6 or Cy7-C11, grafted to the AuNP surface through thiolated bridges of different lengths: the close proximity to the Au surface induces full quenching of the Cy fluorescence, resulting in thermal relaxation on irradiation. Attempts to full coat AuNP with the lipophilic Cy7-C6 and Cy7-C11 lead to precipitation from aqueous solutions. We thus prepared AuNP with partial pegylation (30, 50, or 70 %), using a long chain thiol-terminated PEG bearing a -COOH function. Addition until saturation of either Cy7-C6 or Cy7-C11 to the partially pegylated AuNP gave the AuNP@Cy/PEGX% hybrids (X=30, 50, 70) that are stable in water and in the water/alcohol mixtures used to prepare the nanoinks. Further overcoating of AuNP@Cy7-C6/PEG50 % with PAH (polyallylamine hydrochloride) avoids LSPR hybridization in the dry nanoink printouts, that present two separate bands. When irradiated with laser sources near their absorption maxima, the printouts of the AuNP@Cy7-C6/PEG50 %@PAH nanoink respond on two channels, giving different temperature increases depending on the irradiation wavelengths. This enhances the potentiality of use of these nanoinks for photothermal anticounterfait printouts, making more difficult to reproduce the correct ΔT vs λirradiation output.

Injectable Thermogelling Nanostructured Ink as Simultaneous Optical and Magnetic Resonance Imaging Contrast Agent for Image-Guided Surgery

The development of efficient and biocompatible contrast agents is particularly urgent for modern clinical surgery. Nanostructured materials raised great interest as contrast agents for different imaging techniques, for which essential features are high contrasts, and in the case of precise clinical surgery, minimization of the signal spatial dispersion when embedded in biological tissues. This study deals with the development of a multimodal contrast agent based on an injectable hydrogel nanocomposite containing a lanthanide-activated layered double hydroxide coupled to a biocompatible dye (indocyanine green), emitting in the first biological window. This novel nanostructured thermogelling hydrogel behaves as an efficient tissue marker for optical and magnetic resonance imaging because the particular formulation strongly limits its spatial diffusion in biological tissue by exploiting a simple injection. The synergistic combination of these properties permits to employ the hydrogel ink simultaneously for both optical and magnetic resonance imaging, easy monitoring of the biological target, and, at the same time, increasing the spatial resolution during a clinical surgery. The biocompatibility and excellent performance as contrast agents are very promising for possible use in image-guided surgery, which is currently one of the most challenging topics in clinical research.

A combined experimental and DFT study of metal core/indocyanine green shell hybrid nanoparticles

Indocyanine green (ICG) is the FDA-approved fluorescent dye used for in vivo medical imaging, diagnostics, and photothermal therapy. However, this dye is easily degradable in the human vascular system, and therefore its stabilization is preferable. In this work, ICG molecules were stabilized by their adsorption on the surface of the L-methionine-capped Ag and Au nanoparticles (Ag and Au @LM NPs) in aqueous colloidal dispersions. The result is the formation of hybrid metal core/ICG shell NPs in colloidal dispersions. Additionally, colloidal dispersions were stabilized, indicating a double effect of ICG adsorption. The obtained hybrid NPs were studied experimentally (UV-Vis spectrophotometry, HRTEM, DLS, FTIR) and theoretically (DFT calculations). HRTEM revealed that the interplanar spacing between adjacent planes of NPs decreases after the dye adsorption. The results obtained from the DFT study confirmed the formation of a covalent bond between the oxygen from ICG dye SO3- group and metal NPs. Considering the characteristics of both components of the NPs/ICG hybrid system, the authors assume that this hybrid system can exhibit the synergistic effect that could lead to more successful theranostic treatment of cancer in nanomedicine.

Universal Chiral-Plasmon-Induced Upward and Downward Transfer of Circular Dichroism to Achiral Molecules

Electromagnetic chirality transfer represents an effective means of the nanoscale manipulation of optical chirality. While most of the previous reports have exclusively focused on the circular dichroism (CD) transfer from UV-responsive chiral molecules toward visible-resonant achiral colloidal nanoparticles, here we demonstrate a reverse process in which plasmonic chirality can be transferred to achiral molecules, either upward from visible to UV or downward from visible to near infrared (NIR). By hybridizing achiral UV- or NIR-responsive dye molecules with chiral metal nanoparticles in solution, we observe a chiral-plasmon-induced CD (CPICD) signal at the intrinsically achiral molecular absorption bands. Full-wave electromagnetic modeling reveals that both near-field Coulomb interaction and far-field radiative coupling contribute to the observed CPICD, indicating that the mechanism considered here is universal for different material systems and types of optical resonances. Our study provides a set of design guidelines for broadband nanophotonic chiral sensing from the UV to NIR spectral regime.

Near-infrared light activatable niosomes loaded with indocyanine green and plasmonic gold nanorods for theranostic applications

Light-mediated theranostic platforms involve the use of agents (small molecules/nanomaterials), which can absorb light to produce either heat or reactive chemical species (RCS) and emit fluorescence. Such platforms are advantageous in the field of personalized medicine, as they provide enhanced diagnostic capabilities, improved therapeutic efficiencies, and can also simultaneously monitor the treatment outcomes using imaging modalities. Specifically, agents absorbing near-infrared (NIR) light can provide minimal scattering, low autofluorescence, superior spatio-temporal resolution, and deeper tissue penetration depths. Gold nanorods (GNR) and indocyanine green (ICG) are two agents known to absorb light in the NIR region. GNR can provide tunable plasmonic properties, while ICG is an FDA-approved NIR fluorophore. However, the use of ICG and GNR suffers from various limitations, such as photobleaching, non-specificity, toxicity, and aggregation in solution. To overcome these limitations, herein, we report on NIR light-activatable niosomes loaded with GNR and ICG for cancer theranostic applications. Both agents were encapsulated into non-ionic surfactant-based biocompatible niosomes to form ICG-GNR@Nio with superior loading efficiencies and enhanced properties. ICG-GNR@Nio offers excellent storage stability, photostability, elevated temperature rise and generation of reactive oxygen species (ROS) upon 1064 nm laser irradiation. Subsequently, the enhanced phototherapeutic capabilities mediated by ICG-GNR@Nio were validated in the in vitro cellular experiments. Overall, ICG-GNR@Nio-based theranostic platforms can provide a significant benchmark in the improved diagnosis and therapeutic capabilities for biomedical clinicians to tackle various diseases.

Near IR-plasmon enhanced guided fluorescence and thermal imaging of tissue subsurface target using ICG-labeled gold nanourchin and protein contrast agent: implication of stability

A dual-function nanocomposite agent (NCA) was prepared for deep tissue fluorescence and thermal imaging. The results showed that a combination of some agents such as gold nanourchins (GNU) and indocyanine green (ICG) can have spectral overlapping and hence some peak broadening. Despite 83% and 92% loss of NCA fluorescence after tissue layers L1 and L2, respectively, there was sufficient signal detected for imaging the target buried under the tissue. No fluorescence was detected after L3. A significant contribution was made by GNU for both the fluorescence signal due to the plasmon-enhanced fluorescence (PEF) effect and the thermal heating because of local surface plasmon resonance (LSPR) due to its sharp tips. In the first case, PEF occurred within the first 40 s then followed by a gradual quenching by 23% in 4 min and 72% in the following 6 min. During the second quenching time, the emission signal was blue shifted by 10 nm. Of the three samples, sample 2 (S2) indicated the highest temperature rise ≈ 60 °C in 50 s; sample 3 (S3) produced the lowest temperature of ≈ 33 °C in 250 s after the first layer, thus showing BSA acting as a heat sink. Both the heating and cooling time are determined by the thermal properties of the material such as conductivity and diffusivity. Finally, despite the advantages of PEF, the photostability and quenching rate of a dye molecule must be considered in a dynamic detection monitoring system to account and compensate for the effect of contrast agent quality variation.

Indocyanine Green and Methyl-β-Cyclodextrin Complex for Enhanced Photothermal Cancer Therapy

A feasible and biocompatible supramolecular complex self-assembled from indocyanine green (ICG) and methyl-β-cyclodextrin (Mβ-CD) was developed for targeted cancer imaging, which enhanced fluorescence-guided photothermal cancer therapy. This study confirmed that the formation of an inclusion complex of the heterocyclic ICG moiety and Mβ-CD inner cavity could result in improved tumor targetability compared with free ICG. The ICG-CD complex could be used as a bifunctional phototherapeutic agent for targeted cancer phototherapy due to the high tumor targetability of the Mβ-CD moiety and effective photothermal performance of the near-infrared (NIR) ICG moiety. Upon NIR laser irradiation, the photothermal effect exerted by the ICG-CD complex significantly enhanced the temperature at the tumor site by 56.2 °C within 5 min. Targeting HT-29 tumors using the ICG-CD complex resulted in an apparent reduction in tumor volumes over the 9 days after photothermal treatment. Moreover, no tumor recurrence or body weight loss were observed after administering a single dose of ICG-CD complex with NIR laser irradiation. Therefore, the administration of the biocompatible ICG-CD complex in combination with NIR laser treatment can be safely explored as a potential strategy for future clinical applications.

Study of chemical processes involved in silver staining of gold nanostructures by Raman scattering

Strong Raman enhancement contributed by "hot spots" in directly fused gold dimers offer a selective and sensitive tool for understanding the surface processes involved in the silver staining of gold nanostructures. These processes include the interactions of cations, effects of surface adsorbed Cl(-) ions, surface replacement of ligands, and reduction of silver ions on the surface of the gold nanocrystals. Results show that in the commonly applied silver staining scheme for gold nanostructures, i.e., the addition of the Raman probe after the deposition of the silver shell, the Raman signals of the probe (p-mercaptobenzoic acid) were weakened greatly, due to the pre-existence of the Cl(-)-Ag(+)-citrate bridges on the surface of the gold. A new scheme was developed for silver deposition after pre-adsorption of the probe, which achieved a Raman enhancement factor as high as ∼5 × 10(8).

Effect of metal-liquid interface composition on the adsorption of a cyanine dye onto gold nanoparticles

Synthesis of asymmetric nanoparticles, such as gold nanorods, with tunable optical properties providing metal structures with improved SERS performance is playing a critical role in expanding the use of SERS to imaging and sensing applications. However, the synthetic methods usually require surfactants or polymers as shape-directing agents. These chemicals normally remain firmly bound to the metal after the synthesis, preventing the direct adsorption of a large number of potential analytes and often hampering the chemical functionalization of the surface unless extended, and critical for the nanoparticle stability, postremoval steps were performed. For this reason, it is of great importance for the full exploitation of these nanostructures to gain a deeper insight into the dependence of the analyte-metal interaction to the metal-liquid interface composition. In this article, we investigated in detail the role played by each component of the gold nanorod (GNR) interface in the adsorption of indocyanine green (ICG) as a probe molecule. Citrate-reduced gold nanospheres were used as a model substrate since the negative citrate anions adsorbed onto the metal surface can be easily displaced by those chemicals usually involved in the GNR synthesis, allowing the GNR-like interface composition to be progressively rebuilt and modified at will on the citrate-capped nanoparticles. The obtained results provide a meticulous description of the role played by each individual component of the metal-liquid interface on the ICG interaction with the metal, illustrating how apparently minor experimental changes can dramatically modify the affinity and optical properties of the ICG probe adsorbed onto the nanoparticle.

Indocyanine-green-loaded microballoons for biliary imaging in cholecystectomy

We encapsulate indocyanine green (ICG) in poly[(D,L-lactide-co-glycolide)-co-PEG] diblock (PLGA-PEG) microballoons for real-time fluorescence and hyperspectral imaging of biliary anatomy. ICG-loaded microballoons show superior fluorescence characteristics and slower degradation in comparison with pure ICG. The use of ICG-loaded microballoons in biliary imaging is demonstrated in both biliary-simulating phantoms and an ex vivo tissue model. The biliary-simulating phantoms are prepared by embedding ICG-loaded microballoons in agar gel and imaged by a fluorescence imaging module in a Da Vinci surgical robot. The ex vivo model consists of liver, gallbladder, common bile duct, and part of the duodenum freshly dissected from a domestic swine. After ICG-loaded microballoons are injected into the gallbladder, the biliary structure is imaged by both hyperspectral and fluorescence imaging modalities. Advanced spectral analysis and image processing algorithms are developed to classify the tissue types and identify the biliary anatomy. While fluorescence imaging provides dynamic information of movement and flow in the surgical region of interest, data from hyperspectral imaging allow for rapid identification of the bile duct and safe exclusion of any contaminant fluorescence from tissue not part of the biliary anatomy. Our experiments demonstrate the technical feasibility of using ICG-loaded microballoons for biliary imaging in cholecystectomy.