PDADMAC/Alginate-Coated Gold Nanorod For Eradication of Staphylococcus Aureus Biofilms

Introduction

Over 75% of clinical microbiological infections are caused by bacterial biofilms that grow on wounds or implantable medical devices. This work describes the development of a new poly(diallyldimethylammonium chloride) (PDADMAC)/alginate-coated gold nanorod (GNR/Alg/PDADMAC) that effectively disintegrates the biofilms of Staphylococcus aureus (S. aureus), a prominent pathogen responsible for hospital-acquired infections.

Methods

GNR was synthesised via seed-mediated growth method, and the resulting nanoparticles were coated first with Alg and then PDADMAC. FTIR, zeta potential, transmission electron microscopy, and UV-Vis spectrophotometry analysis were performed to characterise the nanoparticles. The efficacy and speed of the non-coated GNR and GNR/Alg/PDADMAC in disintegrating S. aureus-preformed biofilms, as well as their in vitro biocompatibility (L929 murine fibroblast) were then studied.

Results

The synthesised GNR/Alg/PDADMAC (mean length: 55.71 ± 1.15 nm, mean width: 23.70 ± 1.13 nm, aspect ratio: 2.35) was biocompatible and potent in eradicating preformed biofilms of methicillin-resistant (MRSA) and methicillin-susceptible S. aureus (MSSA) when compared to triclosan, an antiseptic used for disinfecting S. aureus colonisation on abiotic surfaces in the hospital. The minimum biofilm eradication concentrations of GNR/Alg/PDADMAC (MBEC50 for MRSA biofilm = 0.029 nM; MBEC50 for MSSA biofilm = 0.032 nM) were significantly lower than those of triclosan (MBEC50 for MRSA biofilm = 10,784 nM; MBEC50 for MRSA biofilm 5967 nM). Moreover, GNR/Alg/PDADMAC was effective in eradicating 50% of MRSA and MSSA biofilms within 17 min when used at a low concentration (0.15 nM), similar to triclosan at a much higher concentration (50 µM). Disintegration of MRSA and MSSA biofilms was confirmed by field emission scanning electron microscopy and confocal laser scanning microscopy.

Conclusion

These findings support the potential application of GNR/Alg/PDADMAC as an alternative agent to conventional antiseptics and antibiotics for the eradication of medically important MRSA and MSSA biofilms.

Conjugation with gold nanoparticles improves the stability of the KT2 peptide and maintains its anticancer properties

One of the major weaknesses of therapeutic peptides is their sensitivity to degradation by proteolytic enzymes in vivo. Gold nanoparticles (GNPs) are a good carrier for therapeutic peptides to improve their stability and cellular uptake in vitro and in vivo. We conjugated the anticancer KT2 peptide as an anticancer peptide model to PEGylated GNPs (GNPs-PEG) and investigated the peptide stability, cellular uptake and ability of the GNPs-KT2-PEG conjugates to induce MDA-MB-231 human breast cancer cell death. We found that 11 nm GNPs protected the conjugated KT2 peptide from trypsin proteolysis, keeping it stable up to 0.128% trypsin, which is higher than the serum trypsin concentration (range 0.0000285 ± 0.0000125%) reported by Lake-Bakaar, G. et al., 1979. GNPs significantly enhanced the cellular uptake of KT2 peptides after conjugation. Free KT2 peptides pretreated with trypsin were not able to kill MDA-MB-231 cells due to proteolysis, while GNPs-KT2-PEG was still able to exert effective cancer cell killing after trypsin treatment at levels comparable to GNPs-KT2-PEG without enzyme pretreatment. The outcome of this study highlights the utility of conjugated anticancer peptides on nanoparticles to improve peptide stability and retain anticancer ability.

One of the major weaknesses of therapeutic peptides is their sensitivity to degradation by proteolytic enzymes in vivo.

Stealthiness and Hematocompatibility of Gold Nanoparticles with Pre-Formed Protein Corona

Studies have established that a serum protein corona pre-formed around gold nanorods (NRs) could be exploited for loading photosensitizers and chemotherapeutics to result in efficient cell kill in vitro with an extremely low dose. In this study, we further demonstrated that pre-forming a serum protein corona (PC) around citrate-capped NRs (NR-Cit) to form NR-PC conferred them stealth property and high hematocompatibility similar to the common strategy of PEGylating NRs, which would otherwise not be able to evade the immune system. Specifically, the NR-PC caused minimal complement activation with significantly lower formation of the terminal complement complex SC5b-9 measured in human serum containing NR-PC, and this resulted in low uptake by phagocytic U937 monocytes of 5.9% of the initial gold dose compared to 55.8% of NR-Cit. In addition, NR-PC exhibited very low hemolytic activity of less than 0.2% hemolysis with no observable effect on RBC morphology as opposed to 0.6% for NR-Cit at the same concentration of 1 nM NRs. Furthermore, we showed that the high hematocompatibility and stealth property of NR-PC were maintained even after the loading of small molecules, photosensitizer Chlorine e6 (Ce6), into the protein corona, thus further establishing the potential clinical relevance of exploiting the inevitably formed serum protein corona on nanoparticles as an effective delivery vector for small molecular therapeutics.

Dynamics of Human Serum Albumin Corona Formation on Gold Nanorods with Different Surface Ligands In Silico

The interaction between human serum albumin (HSA) and nanoparticles (NPs) to form HSA corona has widely been studied since endogenous functions of albumin are highly attractive for drug delivery. However, a full understanding of the molecular dynamics and factors behind the formation of HSA corona, including interactions between HSA and different surface ligands and between neighboring HSA molecules, resulting in conformational change of HSA is presently lacking. Here, we assembled 14 HSA molecules around gold nanorods (AuNRs) with different surface chemistries (bare gold surface, cetyltrimethylammonium bromide (CTAB), polystyrene sulfonate (PSS), and polydiallyldimethylammonium chloride (PDADMAC)) in silico and examined the dynamics of HSA corona formation using coarse-grained molecular dynamics for 300 ns of simulation. We observed that PDADMAC, being more flexible than PSS, resulted in all HSA molecules moving toward AuNR-PDADMAC, while the instability of CTAB on AuNR resulted in fewer HSA molecules moving toward AuNR-CTAB compared to AuNR-PSS. HSA molecules around AuNR-PDADMAC also exhibited the largest conformational change in terms of their radius of gyration (R_g) and root mean square deviation (RMSD). In the absence of surface ligands, HSA molecules around the bare AuNR were susceptible to steric hindrance with conformational change observed in terms of their RMSD but not their R_g unlike that of HSA molecules around AuNR-PDADMAC. The insights gained from the inclusion of neighboring HSA molecules in the simulation of corona formation could be more representative than examining a single adsorbed HSA molecule on AuNRs with different surface passivations.

In situ measurements of intracellular thermal conductivity using heater-thermometer hybrid diamond nanosensors

Understanding heat dissipation processes at nanoscale during cellular thermogenesis is essential to clarify the relationships between the heat and biological processes in cells and organisms. A key parameter determining the heat flux inside a cell is the local thermal conductivity, a factor poorly investigated both experimentally and theoretically. Here, using a nanoheater/nanothermometer hybrid made of a polydopamine encapsulating a fluorescent nanodiamond, we measured the intracellular thermal conductivities of HeLa and MCF-7 cells with a spatial resolution of about 200 nm. The mean values determined in these two cell lines are both 0.11 ± 0.04 W m^-1 K^-1, which is significantly smaller than that of water. Bayesian analysis of the data suggests there is a variation of the thermal conductivity within a cell. These results make the biological impact of transient temperature spikes in a cell much more feasible, and suggest that cells may use heat flux for short-distance thermal signaling.

Conjugation of Peptides to Gold Nanoparticles

Peptides and proteins have played an important role in many biological processes, functioning as enzymes, hormones, ligands, receptors, cell mediators, and structural components of cells. Being intrinsic molecules in signaling pathways, peptides allow for therapeutic intervention that closely mimic natural signaling cascades. However, the short chain of amino acids in free peptides is susceptible to proteolysis in vivo. Conjugation of peptides onto nanoparticles has been used as a strategy to extend peptide half-life through conferring steric hindrance and a high packing density that prevents proteolytic enzymes to degrade them. Here, we describe a method to conjugate the anticancer p53 peptides as our model peptide onto 12 nm gold nanoparticles (AuNPs) to form the AuNP-p53 peptide conjugate. Conjugation of the p53 short-chain peptide of 25 amino acids occurs through a combination of electrostatic interactions and covalent bonds between cysteine residues at the N-terminal of the peptide and the surface of the AuNPs. The AuNPs and AuNP-p53 are characterized by UV-Vis spectroscopy for its optical absorbance and zetasizer for their hydrodynamic diameter and zeta potential. The semiquantitative analysis of the amount of conjugated peptides on the AuNPs and peptide stability under trypsin treatment is performed on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE).

Innate immune activation by conditioned medium of cancer cells following combined phototherapy with photosensitizer-loaded gold nanorods

Nanoparticle-based phototherapy has evolved to include immunotherapy as an effective treatment combination for cancers through inducing anti-cancer immune activation leading to downstream adaptive responses and immune protection. However, most cancer phototherapy studies that claimed anti-cancer immunogenic effects often included exogenous immunostimulants to potentiate immune responses and did not clearly establish their effects on immune cells. In this study, we showed that combined photodynamic (PDT) and photothermal therapy (PTT) using gold nanorods (NRs) loaded with the photosensitizer chlorin e6 (Ce6) on endogenously formed mouse serum (MS) protein coronas (i.e., NR-MS-Ce6) on EMT6 murine mammary carcinoma cells could potentiate the activation of both J774A.1 macrophages and DC2.4 dendritic cells. The activation of these innate immune cells by the conditioned media from cancer cells treated with combined PDT + PTT was cell-type and number dependent. While treated B16-OVA murine melanoma cells induced lower activation levels for both immune cell types compared to EMT6, they caused higher pro-inflammatory cytokine secretion levels. Our study suggests the importance of immunological investigations to complement any nanoparticle-based therapeutic interventions to better evaluate their efficacy. This could be achieved through a simple approach to screen for the first line of immune responses arising from these therapies prior to in vivo studies.

Light-independent M1 macrophage polarization by photosensitizer-loaded protein corona on gold nanorods

Aim: To establish a light-independent functionality of gold nanorods (AuNRs) with a human serum (HS) protein corona loaded with photosensitizer Chlorin e6 (AuNR-HS-Ce6) in M1 polarization of macrophages. Methods: RT-qPCR and ELISA were used to determine gene and protein expression, respectively. Uptake of AuNR-HS-Ce6 was determined via flow cytometry, inductively coupled plasma mass spectrometry and fluorescence microscopy. Cell viability was determined using PrestoBlue^® cell viability assay. Results: An increase in M1 gene and protein expression was observed in AuNR-HS-Ce6-treated macrophages. Delivery of high Ce6 payload via AuNR-HS-Ce6 was the primary contributor toward M1 polarization. Finally, DLD-1 cells treated with conditioned media from AuNR-HS-Ce6-treated macrophages showed significantly reduced proliferation. Conclusion: Our study suggests an immunomodulatory potential of Ce6 in inducing light-independent M1 polarization outside of its role as a photosensitizer.

Polyelectrolyte stiffness on gold nanorods mediates cell membrane damage

Charge and surface chemistry of gold nanorods (AuNRs) are often considered the predictive factors for cell membrane damage. Unfortunately, extensive research on AuNR passivated with polyelectrolyte (PE) ligand shell (AuNR-PE) has hitherto left a vital knowledge gap between the mechanical stability of the ligand shell and the cytotoxicity of AuNR-PEs. Here, the agreement between unbiased coarse-grained molecular dynamics (CGMD) simulation and empirical outcomes on hemolysis of red blood cells by AuNR-PEs demonstrates for the first time, a direct impact of the mechanical stability of the PE shell passivating the AuNRs on the lipid membrane rupture. Such mechanical stability is ultimately modulated by the rigidity of the PE components. The CGMD simulation results also reveal the mechanism where the PE chain adsorbs near the surface of the lipid bilayer without penetrating the hydrophobic core of the bilayer, which allows the hydrophobic AuNR core to be in direct contact with the hydrophobic interior of the lipid bilayer, thereby perforating the lipid membrane to induce membrane damage.

Rapid Detection of Carbapenemase-Producing Enterobacteriacae Based on Surface-Enhanced Raman Spectroscopy with Gold Nanostars

The emergence and rapid spread of antibiotic resistance poses a serious threat to healthcare systems across the globe. The existence of carbapenemase-producing Enterobacteriaceae (CPE) such as Klebsiella pneumoniae renders the use of carbapenems, the last-resort class of β-lactam antibiotics, ineffective against bacterial infections, often leading to CPE-associated mortalities. Current methods of detection such as the Carba NP test and modified Hodge's test require hours to days to detect, which delays the response to isolate patients for rapid intervention. Here, we developed a surface-enhanced Raman scattering (SERS)-based detection scheme which utilizes gold nanostars conjugated to a β-lactam antibiotic ceftriaxone (CRO) as a beacon for rapid detection of bacterial β-lactamase secreted by Delhi metalloproteinase (NDM)-producing Escherichia coli as our CPE model with carbapenemase activity. The cleavage of β-lactam ring in CRO by NDM (Class B β-lactamase) caused a detectable reduction in SERS intensities at 722, 1358, and 1495 cm^-1 within 25 min. Ratiometric analysis of the SERS peaks at 722, 1358, and 1495 cm^-1 normalized against the Raman peak of polystyrene cuvette at 620 cm^-1 showed the peak at 1358 cm^-1 having the most significant change in intensity upon CPE detection. This reduced detection time has not been reported to date for CPE detection, and our novel approach using SERS could be extended to detect the activity of other classes of β-lactamases to broaden its clinical utility.

Sequestration of Cetyltrimethylammonium Bromide on Gold Nanorods by Human Serum Albumin Causes Its Conformation Change

Serum albumin could potentially be exploited to form a protein corona on gold nanorods (AuNRs) for drug delivery because of its endogenous functionality as a small molecule carrier. However, the cetyltrimethylammonium bromide (CTAB) surfactant, which is a synthesis byproduct passivating AuNRs to confer colloidal stability, could also cause its conformational change upon interaction with serum albumin during the process of corona formation, thus altering its biological functions. Unfortunately, a clear understanding of how exactly human serum albumin (HSA) would change its conformation as it interacts with AuNR-CTAB is presently lacking. Here, we made use of coarse-grain molecular dynamics (CGMD) simulation to elucidate the interaction between HSA and AuNR-CTAB leading to its widely reported conformational change. We showed that HSA could sequester CTAB from the surface of AuNRs and form HSA-CTAB complexes, which could also interact with other adjacent complexes through "cross-linking" by the clusters of CTAB. Such a HSA-CTAB complex resulted in the observed conformational change of HSA, which we verified empirically with an esterase activity assay and by analyzing the root-mean-square-deviation of the HSA molecules from CGMD. The conformational change of HSA was not observed in AuNRs passivated with other negatively or positively charged surface ligands such as polystyrene sulfonate and polydiallyldimethylammonium chloride. Therefore, our study revealed that the conformational change experienced by HSA may not necessarily be attributed to protein unfolding on the surface of the AuNR due to charge interactions but rather to the instability of the surface ligands on the AuNRs which allows them to be sequestered by HSA to form HSA-CTAB complexes.

Innate immune activation by conditioned medium of cancer cells following combined phototherapy with photosensitizer-loaded gold nanorods

Nanoparticle-based phototherapy has evolved to include immunotherapy as an effective treatment combination for cancers through inducing anti-cancer immune activation leading to downstream adaptive responses and immune protection.

Polydopamine Coating Enhances Mucopenetration and Cell Uptake of Nanoparticles

Mucus is an endogenous viscoelastic biopolymer barrier that limits the entry of foreign pathogens and therapeutic carriers to the underlying mucosal cells. This could be overcome with a hydrophilic and nonpositively charged carrier surface that minimizes interactions with the mucin glycoprotein fibers. Although PEGylation remains an attractive surface strategy to enhance mucopenetration, cell uptake of PEGylated nanoparticles (NPs) often remains poor. Here, we demonstrated polydopamine (PDA) coating to enhance both mucopenetration and cell uptake of NPs. PDA was polymerized on carboxylated polystyrene (PS) NPs to form a PDA coating, and the resulting PS-PDA achieved a similar level of mucopenetration as our PEGylated PS (PS-PEG) positive control in three separate studies: NP-mucin interaction test, transwell assay, and multiple particle tracking. Compared to water, the diffusions of PS-PDA and PS-PEG in reconstituted mucus solution were only 3.5 and 2.4 times slower, respectively, whereas the diffusion of bare PS was slowed by up to 250 times. However, the uptake of PS-PDA (61.2 ± 6.1%) was almost three times higher than PS-PEG (24.6 ± 5.4%) in T24 cells, which were used as a model for underlying mucosal cells. Our results showed a novel unreported functionality of PDA coating in enhancing both mucopenetration and cell uptake of NPs for mucosal drug delivery applications, not possible with conventional PEGylation strategies.

Mannitol-induced gold nanoparticle aggregation for the ligand-free detection of viral particles

Addition of osmolytes causes viruses-coated AuNPs to aggregate and not protein-coated AuNPs. Ligand-free detection of virus was developed without the need for prior knowledge of the specific virus target.

Size-dependent neutralizing activity of gold nanoparticle-based subunit vaccine against dengue virus

Dengue results in substantial human morbidity and significant socio-economic impacts, but a specific dengue therapeutic is not available. The currently available dengue vaccine has low efficacy and high rate of adverse effects, necessitating different strategies for the development of a safer and more efficient vaccine against dengue virus. We describe here a hybrid combination of different-sized gold nanoparticles (AuNPs) and domain III of envelope glycoprotein derived from serotype 2 of dengue virus (EDIII) as dengue subunit vaccine. The efficacy of the EDIII-functionalized AuNPs (AuNP-E) to induce neutralizing antibody in BALB/c mice is evaluated. Obtained results show that AuNP-E induced a high level of antibody which mediates serotype-specific neutralization of dengue virus. More importantly, the level of antibody is dependent on both the size of AuNPs and the concentration of AuNP-E, implicating the possibility to modulate it through adjusting these parameters. These results represent an important step towards the development of tetravalent AuNP-based subunit dengue vaccine.

STATEMENT OF SIGNIFICANCE

This research presents a novel subunit vaccine against dengue virus using a hybrid comprising gold nanoparticles (AuNPs) and domain III of envelop protein (EDIII). We proved the neutralizing activity of anti-EDIII antibody induced in immunized mice on Dengue virus serotype 2 in an AuNP core size and concentration dependent manner. The hybrid concept behind this work could also be adopted for the development of a tetravalent vaccine against four serotypes of Dengue virus.

Influence of protein corona and caveolae-mediated endocytosis on nanoparticle uptake and transcytosis

Transcytosis of nanoparticles (NPs) is emerging as an attractive alternative to the paracellular route in cancer drug delivery with studies suggesting targeting caveolae-mediated endocytosis to maximize NP transcytosis. However, there are limited studies on transcytosis of NPs, especially for corona-coated NPs. Most studies focused on cellular uptake as an indirect measure of the NP's transcellular permeability (Pd). Here, we probed the effect of protein corona on the uptake and transcytosis of 20, 40, 100, and 200 nm polystyrene nanoparticles (pNP-PC) across HUVECs in a microfluidic channel that modelled the microvasculature. We observed increased cell uptake with size of pNP-PC although it was the smallest 20 nm pNP-PC that exhibited the highest transcellular Pd. In the absence of corona however, cell uptake decreased with size, and the largest 200 nm pNP-PEG exhibited the lowest transcellular Pd. By inhibiting caveolae-mediated endocytosis in HUVECs, smaller pNPs had a larger drop in cell uptake than larger pNPs, regardless of surface coating. However, only the smallest (20 nm) and largest (200 nm) pNP-PC had a decrease in Pd following inhibition with MβCD. Our findings showed that the protein corona affected the transcytosis of NPs, and their uptake by caveolae-mediated endocytosis did not necessarily lead to transcytosis.

Polydopamine Nanoparticles Enhance Drug Release for Combined Photodynamic and Photothermal Therapy

Our study shows a facile two-step method which does not require the use of core templates to load a hydrophobic photosensitizer drug chlorin e6 (Ce6) within polydopamine (PDA) nanoparticles (NPs) while maintaining the intrinsic surface properties of PDA NPs. This structure is significantly different from hollow nanocapsules which are less stiff as they do not possess a core. To our knowledge, there exist no similar studies in the literature on drug loading within the polymer matrix of PDA NPs. We characterized the drug loading and release behavior of the photosensitizer Ce6 and demonstrated the therapeutic efficacy of the combined photodynamic (PDT) and photothermal therapy (PTT) from Ce6 and PDA, respectively, under a single wavelength of 665 nm irradiation on bladder cancer cells. We obtained a saturated loading amount of 14.2 ± 0.85 μM Ce6 in 1 nM PDA NPs by incubating 1 mg/mL dopamine solution with 140 μM of Ce6 for 20 h. The PDA NPs maintained colloidal stability in biological media, whereas the pi-pi (π-π) interaction between PDA and Ce6 enabled a release profile of the photosensitizer until day 5. Interestingly, loading of Ce6 in the polymer matrix of PDA NPs significantly enhanced the cell uptake because of endocytosis. An increased cell kill was observed with the combined PDT + PTT from 1 nM PDA-Ce6 compared to that with PTT alone with 1 nM PDA and PDT alone with 15 μM equivalent concentration of free Ce6. PDA-Ce6 NPs could be a promising PDT/PTT therapeutic agent for cancer therapy.

Quantitative and Label-Free Detection of Protein Kinase A Activity Based on Surface-Enhanced Raman Spectroscopy with Gold Nanostars

The activity of extracellular protein kinase A (PKA) is known to be a biomarker for cancer. However, conventional PKA assays based on colorimetric, radioactive, and fluorometric techniques suffer from intensive labeling-related preparations, background interference, photobleaching, and safety concerns. While surface-enhanced Raman spectroscopy (SERS)-based assays have been developed for various enzymes to address these limitations, their use in probing PKA activity is limited due to subtle changes in the Raman spectrum with phosphorylation. Here, we developed a robust colloidal SERS-based scheme for label-free quantitative measurement of PKA activity using gold nanostars (AuNS) as a SERS substrate functionalized with bovine serum albumin (BSA)-kemptide (Kem) bioconjugate (AuNS-BSA-Kem), where BSA conferred colloidal stability and Kem is a high-affinity peptide substrate for PKA. By performing principle component analysis (PCA) on the SERS spectrum, we identified two Raman peaks at 725 and 1395 cm^-1, whose ratiometric intensity change provided a quantitative measure of Kem phosphorylation by PKA in vitro and allowed us to distinguish MDA-MB-231 and MCF-7 breast cancer cells known to overexpress extracellular PKA catalytic subunits from noncancerous human umbilical vein endothelial cells (HUVEC) based on their PKA activity in cell culture supernatant. The outcome demonstrated potential application of AuNS-BSA-Kem as a SERS probe for cancer screening based on PKA activity.

Quantifying Vascular Distribution and Adhesion of Nanoparticles with Protein Corona in Microflow

The protein corona has emerged as an important determinant of biological response in nanoparticle (NP) drug delivery. However, there is presently no reported study on how the protein corona affects the behavior of NPs in microflow and its subsequent interactions with the vascular endothelium, which could affect their delivery to the target tumor site regardless of its targeting mechanism. Furthermore, a consensus on the role of physical and surface characteristics of NPs in affecting the margination of NPs is lacking due to different methods of quantifying margination. In this study, we examine how the particle adhesion (PA) method and particle distribution (PD) method quantify the margination of 20, 40, 100, and 200 nm polystyrene NPs (pNPs) differently in fibronectin or pluronic F-127-coated microfluidic straight channels. We found that PA reduced with increasing pNP size, whereas the PD was similar across all pNP sizes regardless of channel coating. We then formed a protein corona on all pNPs (pNPs-PC) and found that the protein corona increased the adhesion of 40-200 nm pNPs in fibronectin-coated channels, with no size dependence between them except for 40 nm, which had significantly higher particle adhesion. The PA method was also dependent on channel coating, whereas the PD method was independent of channel coating. These results suggested that the PA method was more amenable to surface interactions between the pNPs and the channel wall while providing a measure of the amount of NPs that interacted with the channel walls, whereas the PD method provided a representation of their distribution across the channel due to margination. The two methods complement each other to elucidate a more holistic understanding of how different factors might affect a NP's margination in future studies.

Complement Activation by PEGylated Gold Nanoparticles

Gold nanoparticles (AuNPs) are widely used in biomedical applications, but much less is known about their immunological properties, particularly their interaction with the complement system, a key component of innate immunity serving as an indicator of their biocompatibility. Using a library of different-sized AuNPs (10, 20, 40, and 80 nm) passivated with polyethylene glycol (PEG) of different molecular weight ( M_w = 1, 2, 5, and 10 kDa), we demonstrated that citrate-capped AuNPs activated the whole complement system in a size-dependent manner, characterized by the formation of the end-point activation product, SC5b-9, in human serum. Although PEGylation of AuNPs mitigated, but did not abolish, the activation level, complement activation by PEGylated AuNPs was independent of both the core size of AuNPs and the molecular weight of PEG. The cellular uptake of both citrate-capped and PEGylated AuNPs by human U937 promonocytic cells which expresses complement receptors were highly correlated to the level of complement activation. Taken together, our results provided new insights on the innate complement activation by PEGylated AuNPs that are widely considered to be inert biocompatible nanomaterials.

Universal mRNA Translation Enhancement with Gold Nanoparticles Conjugated to Oligonucleotides with a Poly(T) Sequence

DNA-conjugated gold nanoparticles (AuNPs) have been shown to enhance the translation of mRNA. However, the specific sequence on the DNA dictates the specific mRNA to be enhanced. This study describes poly(thymine)-functionalized AuNPs (AuNP-p(T)DNA) capable of enhancing the translation of any mRNA template that is incorporated into pcDNA6 vector with bovine growth hormone (BGH) polyadenylation signal (P(A)). We demonstrated this by incorporating four genes: green fluorescence protein (GFP), general control nonderepressible 5 (GCN5), cAMP-responsive element binding protein 1 (CREB1), and X-box-binding protein 1-spliced (XBP-1S) separately into pcDNA6 vector with BGH P(A) before their expression in HeLa lysate. The addition of AuNP-p(T)DNA to HeLa lysate containing GFP, GCN5, CREB1, and XBP-1S mRNA increased protein synthesis 1.80, 1.99, 1.95, and 2.20 times, respectively. Similar translation enhancement was also observed in a multiplex reaction containing the mRNA of three genes together in the lysate. Complementary p(T)DNA hybridization to the poly(A) tail of the mRNA was critical as the removal of either p(T)DNA or BGH P(A) in XBP-1S mRNA or the replacement of p(T)DNA with p(A)DNA reduced the translation back to baseline level. Finally, an optimum length of 25 nucleotides for the DNA oligomer and a AuNP-p(T)DNA:mRNA ratio of 0.658 achieved a 3.08-fold translation enhancement. The AuNP-p(T)DNA nanoconstruct could be incorporated into commercial cell-free protein synthesis kits as a universal translation enhancer.

Protein corona in drug delivery for multimodal cancer therapy in vivo

The protein corona is inevitably formed on nanoparticles (NPs) when they are introduced in vivo and has been associated with a reduction in targeting yield, immune recognition and rapid blood clearance, leading to poor tumor accumulation. We have recently shown that it is possible to exploit the protein corona for drug delivery by exploiting it for loading and triggering the release of a photosensitizer Chlorin e6 (Ce6) for simultaneous photodynamic (PDT) and photothermal therapy (PTT) in vitro. Here, we extended our previous in vitro studies to evaluate its effectiveness in vivo. Specifically, we pre-formed the protein corona from mouse serum (MS) around gold nanorods (NRs) and loaded it with Ce6 to form NR-MS-Ce6. The intravenous delivery of NR-MS-Ce6 at a dose of 10 mg kg^-1 Au loaded with 9.63 μg kg^-1 Ce6 into tumor-bearing NCr nude mice resulted in their tumor accumulation reaching a peak concentration of 560.3 μg Au per kg tissue (0.0752% dose) within 6 h post-injection. Subsequent localized laser irradiation of the xenograft tumor resulted in a significant tumor temperature increase of 16.85 °C within 20 min. Combined with the simultaneous reactive oxygen species (ROS) production by Ce6 for PDT, complete tumor regression was achieved within 19 days with no tumor regrowth up to 31 days. Similar to other NPs, significant gold accumulation was observed in the major reticuloendothelial system (RES) organs, particularly the liver and spleen, although no acute toxicity was observed histologically 31 days post-treatment. Our results demonstrated for the first time an in vivo application of the protein corona around NPs in the loading and delivery of drugs in small animals. The ease of drug loading and the biocompatibility of the endogenous serum-based protein corona could make it useful for drug delivery and therapeutic applications instead of merely being considered as a biological artefact to be eliminated.

Correction: Complement activation by gold nanoparticles passivated with polyelectrolyte ligands

Correction for ‘Complement activation by gold nanoparticles passivated with polyelectrolyte ligands’ by Quang Huy Quach et al., RSC Adv., 2018, 8, 6616–6619.

Protein Corona around Gold Nanorods as a Drug Carrier for Multimodal Cancer Therapy

A single nanodevice based on gold nanorods (NRs) coloaded with a photosensitizer, Chlorin e6 (Ce6), and a chemotherapeutic, Doxorubicin (Dox), on its endogenously formed human serum (HS) protein corona, i.e., NR-HS-Ce6-Dox was developed with the aim of performing multimodal cancer therapy: photodynamic (PDT), photothermal (PTT) and chemotherapy (CTX) simultaneously upon irradiation with a single 665 nm laser. Here, the excitation of NRs and Ce6 resulted in photothermal ablation (PTT), and production of reactive oxygen species (ROS) to kill Cal 27 oral squamous cell carcinoma (OSCC) cells by oxidative stress (PDT) respectively, while the laser-triggered release of Dox intercalated into the DNA of cancer cells to result in DNA damage and cell death (CTX). High laser-triggered Dox release efficiency of 71.5% and strong plasmonic enhancement of ROS production by Ce6 (4.8-fold increase compared to free Ce6) was observed. Uptake of both Ce6 and Dox by Cal 27 cells was greatly enhanced, with 3.3 and 52 times higher intracellular Dox and Ce6 fluorescence observed, respectively, 6 h after dosing with NR-HS-Ce6-Dox compared to free drugs. The simultaneous trimodal therapy achieved a near complete eradication of cancer cells (98.7% cell death) with an extremely low dose of 15 pM NR-HS-Ce6-Dox loaded with just 1.26 nM Ce6 and 12.5 nM Dox due to strong synergistic enhancement in cancer cell kill compared to individual therapies performed separately. No dark toxicities were observed. These drug concentrations were far lower than any previously reported in vitro, thus eliminating any potential systemic toxicity of these agents.

Exploiting the Anti-Aggregation of Gold Nanostars for Rapid Detection of Hand, Foot, and Mouth Disease Causing Enterovirus 71 Using Surface-Enhanced Raman Spectroscopy

Enterovirus 71 (EV71) is a major public health threat that requires rapid point-of-care detection. Here, we developed a surface-enhanced Raman spectroscopy (SERS)-based scheme that utilized protein-induced aggregation of colloidal gold nanostars (AuNS) to rapidly detect EV71 without the need for fabricating a solid substrate, Raman labels or complicated sample handling. We used AuNS (hydrodynamic diameter, DH of 105.12 ± 1.13 nm) conjugated to recombinant scavenger receptor class B, member 2 (SCARB2) protein with known affinity to EV71. In the absence of EV71, AuNS-SCARB2 aggregated in biological media and produced four enhanced Raman peaks at 390, 510, 670, and 910 cm-1. In the presence of EV71, the three peaks at 510, 670, and 910 cm-1 disappeared, while the peak at 390 cm-1 diminished in intensity as the virus bound to AuNS-SCARB2 and prevented them from aggregation. These three peaks (510, 670, and 910 cm-1) were potential markers for specific detection of EV71 as their disappearance was not observable with a different dengue virus (DENV) as our control. Furthermore, the Raman measurements from colloidal SERS were more sensitive in probing the aggregation of AuNS-SCARB2 for detecting the presence of EV71 in protein-rich samples compared to UV-vis spectrum measurements. With this facile "anti-aggregation" approach, we were able to detect EV71 in protein-rich biological medium within 15 min with reasonable sensitivity of 107 pfu/mL and minimal sample preparation, making this translatable for point-of-care applications.

A Facile Method to Probe the Vascular Permeability of Nanoparticles in Nanomedicine Applications

The effectiveness of nanoparticles (NP) in nanomedicine depends on their ability to extravasate from vasculature towards the target tissue. This is determined by their permeability across the endothelial barrier. Unfortunately, a quantitative study of the diffusion permeability coefficients (P_d) of NPs is difficult with in vivo models. Here, we utilize a relevant model of vascular-tissue interface with tunable endothelial permeability in vitro based on microfluidics. Human umbilical vein endothelial cells (HUVECs) grown in microfluidic devices were treated with Angiopoietin 1 and cyclic adenosine monophosphate (cAMP) to vary the P_d of the HUVECs monolayer towards fluorescent polystyrene NPs (pNPs) of different sizes, which was determined from image analysis of their fluorescence intensity when diffusing across the monolayer. Using 70 kDa dextran as a probe, untreated HUVECs yielded a P_d that approximated tumor vasculature while HUVECs treated with 25 μg/mL cAMP had P_d that approximated healthy vasculature in vivo. As the size of pNPs increased, its P_d decreased in tumor vasculature, but remained largely unchanged in healthy vasculature, demonstrating a trend similar to tumor selectivity for smaller NPs. This microfluidic model of vascular-tissue interface can be used in any laboratory to perform quantitative assessment of the tumor selectivity of nanomedicine-based systems.

Exploiting the Protein Corona from Cell Lysate on DNA Functionalized Gold Nanoparticles for Enhanced mRNA Translation

This study describes the use of DNA functionalized gold nanoparticles (AuNPs) to enhance the synthesis of proteins in cell lysate and examines the mechanisms behind the enhanced mRNA translation. With an appropriate DNA oligomer sequence that hybridizes to the 3'-untranslated region of two mRNA of interest, insulin and green fluorescent protein (GFP), we found that these DNA conjugated AuNPs (AuNP-DNA) introduced into HeLa cell lysate enhanced the synthesis of insulin and GFP by up to 2.18 and 1.80-fold, respectively, over baseline production with just the mRNA present. The insulin synthesis was markedly reduced with non-DNA citrate-capped AuNP (1.25-fold) and AuNP-DNA with a nonspecific poly(T) sequence (1.25-fold). We showed that both nonspecific adsorption of ribosomes and translation factors to form a lysate protein corona on AuNP-DNA and weak hybridization between DNA oligomers and mRNA of interest were important factors that brought translation factors, ribosomes, and mRNA into close proximity of each other. This could reduce the recycling time of ribosomes during mRNA translation, thereby increasing the efficiency of protein synthesis. The outcome of this work shows that with rational DNA design, it could be possible to modulate intracellular biological processes with AuNP-DNA and increase their production of proteins for various biomedical applications.

Optimizing the SERS enhancement of a facile gold nanostar immobilized paper-based SERS substrate

Schematic of study to optimize the SERS enhancement factor of a low cost and facile gold nanostar (AuNS)-based paper-SERS substrate through optimizing the paper materials, immobilization strategies, and SERS acquisition conditions.

Exploiting the protein corona around gold nanorods for low-dose combined photothermal and photodynamic therapy

A nanodevice comprising human serum (HS) protein corona coated gold nanorods (NRs) has been developed to perform both photothermal therapy (PTT) and photodynamic therapy (PDT) simultaneously at a very low dose under irradiation by a single laser. Here, we exploit the protein corona to load a photosensitizer, chlorin e6 (Ce6), to form NR-HS-Ce6, whose excitation wavelength matches with the longitudinal surface plasmon resonance (LSPR) of NRs. When excited by a single laser, the NRs caused photothermal ablation of cancer cells while Ce6 simultaneously produced reactive oxygen species (ROS) to kill cancer cells through oxidative stress in PDT. We found that the protein corona did not affect the photothermal heating of NRs and observed more than 5-fold increase in ROS generation when Ce6 was loaded on NR-HS compared to free HS-Ce6 dissolved in HS. The uptake of Ce6 by Cal 27 oral squamous cell carcinoma (OSCC) cells also increased 57-fold when loaded on NR-HS compared to free HS-Ce6. While both PDT and PTT have established modest success in reducing cancer cell viability on their own, we have shown that the combined therapy can achieve near complete eradication (95.2% cell kill) of cancer cells even at an extremely low dose of 50 pM of NR-HS-Ce6 containing an equivalent of 7.67 μg mL^-1 Au and 4.83 nM Ce6. This near complete cell kill at such a low dose has not been reported previously. The advantages of this nanoscale delivery system showcase the application of protein corona in cancer treatment instead of considering it as an undesirable biological artefact.

Aggregation and protein corona formation on gold nanoparticles affect viability and liver functions of primary rat hepatocytes

AIM

We examined the impact of aggregation and protein corona formation of gold nanoparticles (AuNPs) on the cytotoxicity, uptake and metabolism, specifically urea and albumin synthesis, of primary rat hepatocytes.

MATERIALS & METHODS

The AuNPs were synthesized via citrate reduction and the human serum protein corona was preformed on the AuNPs. Primary hepatocytes were isolated from male Wistar rats via two-step in situ collagenase perfusion method, and were dosed with both citrate-capped (AuNP-Cit) and protein corona coated AuNPs (AuNP-Cor).

RESULTS

The AuNP-Cor showed higher cell uptake and reduced cell viability compared with aggregated AuNP-Cit. Urea and albumin secretions showed AuNP dose dependency. Both AuNP-Cit and AuNP-Cor exerted only an acute effect on the albumin synthesis of hepatocytes with no chronic impact.

Component-Specific Analysis of Plasma Protein Corona Formation on Gold Nanoparticles Using Multiplexed Surface Plasmon Resonance

At the nano-bio interface, human plasma differentially interacts with engineered nanomaterials through the creation of protein coronas, which in turn become primary determinants of both the pharmacokinetics and pharmacodynamics of circulating nanoparticles. Here, for the first time, the specific binding kinetics of the four major corona forming proteins (human serum albumin, fibrinogen, ApoA1, and polyclonal IgG) are determined for gold nanoparticles (AuNPs). Using a multiplexed surface plasmonic assay, highly reproducible measurements of on rate (k(on)), off rate (k(off)), and disassociation constant (K(D)), in addition to relative amounts of protein binding, are obtained. Dramatic differences in k(on) for individual components are shown as primary determinants of protein affinities, with k(on) ranging over nearly two orders of magnitude for the proteins studied, while k(off) remains within a factor of two for the set. The effect of polyethylene glycol (PEG) modification on plasma component binding is also studied and the effect of PEG length on human serum interaction is characterized through systematic screening of PEG molecular weight (2-30k). The effect of nanoparticle modification on particle targeting is also characterized through study of a hybrid AuNP system.

Nanoparticle drug delivery systems and their use in cardiac tissue therapy

Cardiovascular diseases make up one of the main causes of death today, with myocardial infarction and ischemic heart disease contributing a large share of the deaths reported. With mainstream clinical therapy focusing on palliative medicine following myocardial infarction, the structural changes that occur in the diseased heart will eventually lead to end-stage heart failure. Heart transplantation remains the only gold standard of cure but a shortage in donor organs pose a major problem that led to clinicians and researchers looking into alternative strategies for cardiac repair. This review will examine some alternative methods of treatment using chemokines and drugs carried by nanoparticles as drug delivering agents for the purposes of treating myocardial infarction through the promotion of revascularization. We will also provide an overview of existing studies involving such nanoparticulate drug delivery systems, their reported efficacy and the challenges facing their translation into ubiquitous clinical use.

An instantaneous colorimetric protein assay based on spontaneous formation of a protein corona on gold nanoparticles

Commercial protein assays used ubiquitously in laboratories typically require long incubation times due to the inherently slow protein-reagent reactions. In this study, we report a novel facile technique for the instantaneous measurement of total protein concentration by exploiting the rapid aggregation dynamics of gold nanoparticles (NPs). By adsorbing different amounts of proteins on their surface to form a protein corona, these NPs can be sterically stabilized to different degrees by aggregation, thus exhibiting a spectrum of color change which can be quantitatively characterized by UV-Vis absorption spectroscopy. We evaluated this technique on four model proteins with different structures: bovine serum albumin (BSA), normal mouse immunoglobulin G (IgG), fibrinogen (FBG) and apolipoprotein A-I (Apo-A1) using two approaches, sequential and simultaneous. We obtained an approach-dependent linear concentration range up to 80 μg mL(-1) and 400 μg mL(-1) for sequential and simultaneous approaches, respectively. This linear working range was wider than that of the commercial Bradford assay and comparable to the Micro BCA assay. The simultaneous approach was also able to produce a linear working range of 200 to 1000 μg mL(-1) (R(2) = 0.995) in human urine, while the sequential approach was non-functional in urine. Similar to Micro BCA, the NP-based protein assay was able to elicit a linear response (R(2) > 0.87) for all four proteins with different structures. However, unlike Micro BCA which requires up to 120 min of incubation, we were able to obtain the read-out almost instantaneously without the need for incubation. The NP-based technique using the simultaneous approach can thus be exploited as a novel assay for instantaneous protein quantification to increase the productivity of laboratory processes.

Understanding aggregation-based assays: nature of protein corona and number of epitopes on antigen matters

In this study, we systematically examine how the nature of the protein corona on NPs, formed from either antibody or antigen, and how the number of binding sites or epitopes on the antigen affect aggregation.

Protein coronas on gold nanorods passivated with amphiphilic ligands affect cytotoxicity and cellular response to penicillin/streptomycin

We probe how amphiphilic ligands (ALs) of four different types affect the formation of protein coronas on gold nanorods (NRs) and their impact on cellular response. NRs coated with cetyltrimethylammonium bromide were ligand exchanged with polyoxyethylene[10]cetyl ether, oligofectamine, and phosphatidylserine (PS). Protein coronas from equine serum (ES) were formed on these NR-ALs, and their colloidal stability, as well as cell uptake, proliferation, oxidative stress, and gene expression, were examined. We find that the protein corona that forms and its colloidal stability are affected by AL type and that the cellular response to these NR-AL-coronas (NR-AL-ES) is both ligand and corona dependent. We also find that the presence of common cell culture supplement penicillin/streptomycin can impact the colloidal stability and cellular response of NR-AL and NR-AL-ES, showing that the cell response is not necessarily inert to pen/strep when in the presence of nanoparticles. Although the protein corona is what the cells see, the underlying surface ligands evidently play an important role in shaping and defining the physical characteristics of the corona, which ultimately impacts the cellular response. Further, the results of this study suggest that the cellular behavior toward NR-AL is mediated by not only the type of AL and the protein corona it forms but also its resulting colloidal stability and interaction with cell culture supplements.

Optimizing the properties of the protein corona surrounding nanoparticles for tuning payload release

We manipulate the passive release rates of DNA payloads on protein coronas formed around nanoparticles (NPs) by varying the corona composition. The coronas are prepared using a mixture of hard and soft corona proteins. We form coronas around gold nanorods (NRs), nanobones (NBs), and carbon nanotubes (CNTs) from human serum (HS) and find that tuning the amount of human serum albumin (HSA) in the NR-coronas (NR-HS-DNA) changes the payload release profile. The effect of buffer strength, HS concentration, and concentration of the cetyltrimethylammonium bromide (CTAB) passivating the NP surfaces on passive release is explored. We find that corona properties play an important role in passive release, and concentrations of CTAB, HS, and phosphate buffer used in corona formation can tune payload release profiles. These advances in understanding protein corona properties bring us closer toward developing a set of basic design rules that enable their manipulation and optimization for particular biological applications.

Nanoparticle interface to biology: applications in probing and modulating biological processes

Nanomaterials can be considered as "pseudo" subcellular entities that are similar to endogenous biomolecules because of their size and ability to interact with other biomolecules. The interaction between nanoparticles and biomolecules gives rise to the nano-bio interface between a nanoparticle and its biological environment. This is often defined in terms of the biomolecules that are present on the surface of the nanoparticles. The nano-bio interface alters the surface characteristics and is what the biological system sees and interacts with. The nanoparticle can thus be viewed as a "scaffold" to which molecules are attached. Intelligent design of this nano-bio interface is therefore crucial to the functionality of nanoscale systems in biology. In this review, we discuss the most common nano-bio interfaces formed from molecules including DNA, polymers, proteins, and antibodies, and discuss their applications in probing and modulating biological processes. We focus our discussion on the nano-bio interface formed on gold nanoparticles as our nanoparticle "scaffold" of interest in part because of our research interest as well as their unique physicochemical properties. While not exhaustive, this review provides a good overview of the latest advances in the use of gold nanomaterial interface to probe and modulate biological processes.

Stability and aggregation assays of nanoparticles in biological media

Colloidal stability of nanoparticles in biological media is crucial to preserve their utility as aggregation often leads to undesirable biological response. A quantitative measurement of nanoparticles aggregation in solution would provide a valuable assessment of colloidal stability of bio-nano interfaces after surface functionalization. Here, we develop a quantitative technique based on optical absorption to assay the colloidal stability of plasmonic nanoparticles functionalized with different amphiphilic surface ligands in biologically relevant media.

Dark-field circular depolarization optical coherence microscopy

Optical coherence microscopy (OCM) is a widely used structural imaging modality. To extend its application in molecular imaging, gold nanorods are widely used as contrast agents for OCM. However, they very often offer limited sensitivity as a result of poor signal to background ratio. Here we experimentally demonstrate that a novel OCM implementation based on dark-field circular depolarization detection can efficiently detect circularly depolarized signal from gold nanorods and at the same time efficiently suppress the background signals. This results into a significant improvement in signal to background ratio.

Stability of gold nanorods passivated with amphiphilic ligands

The stability of gold nanorods (NRs) coated with amphiphilic ligands (ALs) was investigated. NRs coated with cetyltrimethylammonium bromide (CTAB) were ligand exchanged with polyoxyethylene [10] cetyl ether (Brij56), Oligofectamine (OF), and phosphatidylserine (PS). An aggregation index based on the longitudinal surface plasmon resonance peak broadening was used to measure stability of the NR-ALs under different conditions including the number of washes, pH, ionic concentration, and temperature. The aggregation index was also used to measure the stability of the NR-ALs under ultrafast laser irradiation and in the presence of proteins commonly used in cell culture. Differences in NR-AL stability were found, which were due to differences in the physical and chemical properties of the ALs. Apart from the charge on the AL headgroup, we suggest the Gibbs free energy of passivation (ΔG(p)) and enthalpy of passivation (ΔH(p)) of the AL could potentially aid in the selection of amphiphiles that can effectively passivate NRs for stability and optimize their properties and desired biological impact.

Critical parameters in the pegylation of gold nanoshells for biomedical applications: an in vitro macrophage study

Pegylation of gold nanoshells provides an effective means to reduce their reticuloendothelial system (RES) clearance in body. In this study, we perform a parametric investigation on the factors that would affect the macrophage uptake of gold nanoshells with the aim to optimize their pegylation and minimize their macrophage uptake. We synthesized and pegylated the gold nanoshells using methoxy-poly(ethylene glycol)-thiol and employed an in vitro macrophage assay to examine the effect of surface density of poly(ethylene glycol) (PEG), chain length of the PEG, and size of the gold nanoshells on their macrophage uptake. We have shown that a saturated surface density would minimize macrophage uptake, which could be obtained by experimental titration-based Ellman's reagent. Our results suggest that the chain length of PEG and size of gold nanoshells influence the surface density of PEG. We have also shown that PEG with molecular weight of around 2000Da and a size range larger than 186nm would be appropriate for facilitating a high surface density. Our in vitro macrophage system thus provides a good model to accurately predict the RES response to different pegylation parameters.

Control of optical contrast using gold nanoshells for optical coherence tomography imaging of mouse xenograft tumor model in vivo

The control of image contrast is essential toward optimizing a contrast enhancement procedure in optical coherence tomography (OCT). In this study, the in vivo control of optical contrast in a mouse tumor model with gold nanoshells as a contrast agent is examined. Gold nanoshells are administered into mice, with the injected dosage and particle surface parameters varied and its concentration in the tumor under each condition is determined using a noninvasive theoretical OCT modeling technique. The results show that too high a concentration of gold nanoshells in the tumor only enhances the OCT signal near the tissue surface, while significantly attenuating the signal deeper into the tissue. With an appropriate dosage, IV delivery of gold nanoshells allows a moderate concentration of 6.2 x 10(9) particles/ml in tumor to achieve a good OCT signal enhancement with minimal signal attenuation with depth. An increase in the IV dosage of gold nanoshells reveals a corresponding nonlinear increase in their tumor concentration, as well as a nonlinear reduction in the fractional concentration of injected gold nanoshells. Furthermore, this fractional concentration is improved with the use of antiepodermal growth factor receptor (EGFR) surface functionalization, which also reduces the time required for tumor delivery from 6 to 2 h.

Concentration dependence of gold nanoshells on the enhancement of optical coherence tomography images: a quantitative study

The effective use of gold nanoshells as a contrast agent for optical coherence tomography (OCT) may be hampered by the delivery of a wrong dose to tissue that results in unwanted signal attenuation. In this study we examine how changes in mu(s) due to concentration variations affect the OCT image and then define a dosing range that would result in appropriate scattering coefficient, mu(s), to maintain an acceptable signal attenuation level. Our results show that an increase in sample mu(s) not only enhances the OCT signal near the surface but also attenuates the signal deeper into the sample. We synthesized gold nanoshells with an 81 nm radius silica core and 23 nm shell thickness and found that a concentration range of 5.6 x 10(9)<c<2.3 x 10(10) particles/ml provided adequate signal enhancement near the surface without severely compromising the imaging depth due to signal attenuation. We also demonstrate the extraction of mu(s) from the OCT signal to estimate the gold nanoshells' concentration in vivo and verified that the estimated concentration of 6.2 x 10(9) particles/ml in a mouse tumor after intravenous delivery lies within this concentration range to effectively enhance the tumor image.