Phospholipid Encapsulated AuNR@Ag/Au Nanosphere SERS Tags with Environmental Stimulus Responsive Signal Property

Ultrasensitive detection of thiram based on surface-enhanced Raman scattering via Au@Ag@Ag core/shell/shell bimetallic nanorods

We developed a highly sensitive and stable SERS-active substrate of Au@Ag@Ag core/shell/shell nanorods, formed by encapsulating Au nanorods (Au NRs) into a bilayer silver shell with Raman reporter molecules (4-mercaptobenzoic acid (4-MBA) and thiram) in the shell-shell gap. The core/shell/shell nanostructures demonstrated a high SERS enhancement and easy assembly. The important role of the bilayer silver shell in boosting the SERS intensity and detection sensitivity was revealed by comparing the performances of the Au@Ag@4-MBA@Ag NRs, Au@Ag@4-MBA NRs, and Au@4-MBA NRs. The obtained Au@Ag@4-MBA@Ag NRs exhibited a significantly promoted SERS intensity, which could reach around 2.6 times and 240 times that of the Au@Ag@4-MBA NRs and Au@4-MBA NRs, where the enhancement factor was found to be strongly correlated with the shell thickness. The controllable plasma properties and SERS effect of the Au@Ag@4-MBA@Ag NRs could be optimized by adjusting the dose of silver nitrate. The SERS substrate comprising core/shell/shell nanorods was highly reproducible and stable (retaining 83% SERS intensity after one month). Moreover, the highly sensitive detection of the pesticide thiram with a detection limit as low as 1.74 × 10-9 M was achieved by taking advantage of the great SERS response of the core/shell/shell nanostructures, which was 1-2 orders of magnitude lower than for other SERS substrates. The developed SERS substrate could be readily extended to embed other target analytes into the core/shell/shell nanostructure for novel and sensitive detection. This study could enable fresh approaches toward next-generation ultrasensitive analyte detection.

Stimuli-responsive SERS biosensor for ultrasensitive tetracycline sensing using EDTA-driven PEI@CaCO3 microcapsule and CS@FeMMs

In this work, a stimuli-responsive SERS biosensor was fabricated for tetracycline (TTC) by "signal-on" strategy using (EDTA)-driven polyethyleneimine grafted calcium carbonate (PEI@CaCO₃) microcapsule and chitosan-Fe magnetic microbeads (CS@FeMMs). Initially, aptamer conjugated magnetic-bead CS@FeMMs@Apt with superparamagnetism and excellent biocompatibility was employed as capture probe, which facilitated the rapid and easy magnetic separation. Subsequently, the PEI cross-linked layer and aptamer network layer were constructed onto the outer layer of CaCO₃@4-ATP microcapsule to form sensing probes (PEI@CaCO₃@4-ATP@Apt) via the layer-by-layer assembly method. In the presence of TTC, a sandwich SERS-assay was exploited by aptamer recognition induced target-bridged strategy. When the solution of EDTA was added, the core layer of CaCO₃ would be dissolved quickly, destroying the microcapsule to release 4-ATP. The released 4-ATP could be quantitatively monitored by dripping the supernatant onto the AuNTs@PDMS SERS platform, resulting in a strong Raman "signal-on". Under the optimal conditions, a good linear relationship was established with a correlation coefficient (R²) of 0.9938 and a LOD of 0.03 ng/mL. Additionally, the application capacity of the biosensor to detect TTC was also affirmed in food matrixes, and the results were consistent with the standard ELISA method (P > 0.05). Hence, this SERS biosensor affords extensive application prospects for TTC detection with multiple merits such as high sensitivity, environment friendliness, and high stability.

Microfluidic SERS devices: brightening the future of bioanalysis

A new avenue has opened up for applications of surface-enhanced Raman spectroscopy (SERS) in the biomedical field, mainly due to the striking advantages offered by SERS tags. SERS tags provide indirect identification of analytes with rich and highly specific spectral fingerprint information, high sensitivity, and outstanding multiplexing potential, making them very useful in in vitro and in vivo assays. The recent and innovative advances in nanomaterial science, novel Raman reporters, and emerging bioconjugation protocols have helped develop ultra-bright SERS tags as powerful tools for multiplex SERS-based detection and diagnosis applications. Nevertheless, to translate SERS platforms to real-world problems, some challenges, especially for clinical applications, must be addressed. This review presents the current understanding of the factors influencing the quality of SERS tags and the strategies commonly employed to improve not only spectral quality but the specificity and reproducibility of the interaction of the analyte with the target ligand. It further explores some of the most common approaches which have emerged for coupling SERS with microfluidic technologies, for biomedical applications. The importance of understanding microfluidic production and characterisation to yield excellent device quality while ensuring high throughput production are emphasised and explored, after which, the challenges and approaches developed to fulfil the potential that SERS-based microfluidics have to offer are described.

The SARS-CoV-2 envelope protein disrupts barrier function in an in vitro human blood-brain barrier model

Patients with coronavirus disease 2019 (COVID-19) have been frequently reported to exhibit neurological manifestations and disruption of the blood-brain barrier (BBB). Among the risk factors for BBB breakdown, the loss of endothelial cells and pericytes has caused widespread concern. Recent studies have revealed that severe acute respiratory syndrome coronavirus 2 envelope (S2E) protein caused cell death. We tested the hypothesis that the S2E protein alone could induce BBB dysfunction. The S2E protein bound to human BBB-related cells and inhibited cell viability in a dose- and time-dependent manner. Importantly, the S2E protein disrupted barrier function in an in vitro BBB model composed of HCMEC/D3 (brain endothelial cell line), HBVP (brain vascular pericyte), and U87MG (astrocyte cell line) cells and suppressed the expression of major genes involved in maintaining endothelial permeability and function. In addition, the S2E protein crossed the HCMEC/D3 monolayer. The S2E protein triggered inflammatory responses in HCMEC/D3 and U87MG cells. Taken together, these results show for the first time that the S2E protein has a negative impact on the BBB. Therapies targeting the S2E protein could protect against and treat central nervous system manifestations in COVID-19 patients.

Design and synthesis of gold nanostars-based SERS nanotags for bioimaging applications

Surface-enhanced Raman spectroscopy (SERS) nanotags hold a unique place among bioimaging contrast agents due to their fingerprint-like spectra, which provide one of the highest degrees of detection specificity. However, in order to achieve a sufficiently high signal intensity, targeting capabilities, and biocompatibility, all components of nanotags must be rationally designed and tailored to a specific application. Design parameters include fine-tuning the properties of the plasmonic core as well as optimizing the choice of Raman reporter molecule, surface coating, and targeting moieties for the intended application. This review introduces readers to the principles of SERS nanotag design and discusses both established and emerging protocols of their synthesis, with a specific focus on the construction of SERS nanotags in the context of bioimaging and theranostics.

Plasmonic Metasurfaces Based on Pyramidal Nanoholes for High-Efficiency SERS Biosensing

An inverted pyramidal metasurface was designed, fabricated, and studied at the nanoscale level for the development of a label-free pathogen detection on a chip platform that merges nanotechnology and surface-enhanced Raman scattering (SERS). Based on the integration and synergy of these ingredients, a virus immunoassay was proposed as a relevant proof of concept for very sensitive detection of hepatitis A virus, for the first time to our best knowledge, in a very small volume (2 μL), without complex signal amplification, allowing to detect a minimal virus concentration of 13 pg/mL. The proposed work aims to develop a high-flux and high-accuracy surface-enhanced Raman spectroscopy (SERS) nanobiosensor for the detection of pathogens to provide an effective method for early and easy water monitoring, which can be fast and convenient.

Facile synthesis of silver/gold alloy nanoparticles for ultra-sensitive rhodamine B detection

The synthesis of Ag/Au nanoparticles (NPs) in a controlled manner has been a challenge for a long time. The aim of this report is to present a systematic study on the fabrication, characterization of Ag/Au alloy NP-based surface-enhanced Raman spectroscopy (SERS) substrates. Silver (Ag) and gold (Au) colloidal NPs were prepared by chemical reduction route of the corresponding metal salts by trisodium citrate (TSC). Ag/Au alloy nanoparticles with varying molar fractions are prepared in aqueous solution by the simultaneous reduction of AgNO3 and HAuCl4 by TSC. The composition of Ag and Au in the alloy samples was controlled by tuning the molar ratio of Ag+/Au3+ in the mixture solution. The morphologies of the different products were characterized by TEM, and the size of obtained samples was in the range of 40 to 60 nm. The resulting samples were denoted as AgNPs, AuNPs, Ag3Au, AgAu, and AgAu3 NPs. In order to compare the optical property of the Ag/Au alloy and Ag/Au mixture, we mixed the pure Ag and Au NPs with different ratios to obtain the aggregated nanoparticles. Ag/Au alloy NPs were demonstrated as an ultrasensitive SERS substrate for the detection of rhodamine B (RhB) molecules. The concentration of RhB ranged from 10-11 to 10-5 M. The effect of the Au content on the optical and SERS properties of the Ag/Au alloys was studied. The obtained results show that the Au content in the Ag/Au alloys play an important role in the physical properties of Ag/Au alloy NPs. The SERS spectra of RhB from the as-prepared Ag/Au alloy NP substrates indicated the superior enhancement with high reproducibility and sensitivity compared to those of Ag or Au samples. Interestingly, the highest SERS activity was achieved for the Ag3Au sample with an enhancement factor larger than 1010 for 10-11 M RhB and a limit of detection (LOD) at 10-11 M, as well as good long-term stability after storage for 1 year. As far as we know, this is the highest sensitivity record of RhB by SERS detection. Furthermore, the composition-dependent SERS activity was explained in detail. These advantages demonstrated the potential for growing Ag/Au alloy NP-based SERS substrates in food safety and bioanalysis.

Tunable LSPR of silver/gold bimetallic nanoframes and their SERS activity for methyl red detection

Ag/Au bimetallic nanostructures have received much attention in surface-enhanced Raman scattering (SERS). However, the synthesis of this nanostructure type still remains a challenge. In the present research, Ag/Au nanoframes were synthesized via a simple room temperature solution phase chemical reduction method using pre-synthesized triangular Ag nanoplates as templates in the presence of appropriate amounts of HAuCl4. Controlling experimental parameters was applied for understanding of the growth mechanism. The galvanic exchange reaction resulted in a uniform deposition of the Au shell on the Ag nanoplates and the Ag core was removed which generated triangular hollow nanoframes. It is found that the amount of HAuCl4 added to the growth solution played a key role in controlling the Ag/Au nanoframes. The resultant silver/gold nanoframes with average size of 50 nm were applied in detecting methyl red (MR) in the solution-phase using an excitation wavelength laser of 532 nm. The SERS signal was greatly enhanced owing to the tunable plasmonic peaks in the visible region (400-650 nm). The limit of detection (LOD) of MR in diluted solution was 10-6 M. The enhancement factor (EF) was about 8 × 104 toward 10-5 M of MR. Interestingly, the linear dependence between the logarithm of the SERS signal intensity (log I) and the logarithm of the MR concentration (log C) occurred in the range from 10-6 to 10-4 M. Our work promises the application of Ag/Au nanoframes as a chemical sensor in detecting MR molecules at low concentration with high performance.

Effects of Conformational Variation on Structural Insights from Solution-Phase Surface-Enhanced Raman Spectroscopy

Surface-enhanced Raman scattering (SERS) spectra contain information on the chemical structure on nanoparticle surfaces through the position and alignment of molecules with the electromagnetic near field. Time-dependent density functional theory (TDDFT) can provide the Raman tensors needed for a detailed interpretation of SERS spectra. Here, the impact of molecular conformations on SERS spectra is considered. TDDFT calculations of the surfactant cetyltrimethylammonium bromide with five conformers produced more accurate unenhanced Raman spectra than a simple all-trans structure. The calculations and measurements also demonstrated a loss of structural information in the CH2/CH3 scissor vibration band at 1450 cm-1 in the SERS spectra. To study lipid bilayers, TDDFT calculations on conformers of methyl phosphorylcholine and cis-5-decene served as models for the symmetric choline stretch in the lipid headgroup and the C═C stretch in the acyl chains of 1,2-oleoyl-glycero-3-phosphocholine. Conformer considerations enabled a measurement of the distribution of double-bond orientations with an order parameter of SC═C = 0.53.

SERS-based immunoassay and degradation of CA19-9 mediated by gold nanowires anchored magnetic-semiconductor nanocomposites

Here, straight upward Au nanowires (NWs) were successfully grown onto Fe₃O₄@TiO₂ matrix through a seed-mediated strategy to intensively improve its photocatalysis and SERS performances, facilitating a peculiar recyclable surface-enhanced Raman spectroscopy (SERS)-based immunoassay of CA19-9 in liquid form based on visible light irradiation. Such immunoassay was also supported by a smart heterobifunctional cross-linking agent-mediated probe of anti-CA19-9/4-MBA without metal nanoparticles. A low limit of detection of 5.65 × 10^-4 IUmL^-1 and a wide linear range from 1000 to 0.001 IUmL^-1 were demonstrated through repeated constructing the sandwich immunostructure with only one batch of nanocomposites. Moreover, the actual levels of CA19-9 for colorectal cancer patients were readily measured by the recyclable immunoassay, the results of which are principally consistent with the conventional CLIA detection. Thus, such a green strategy of visible light-induced recyclable immunoassay could be expected to have a potential practicability in the clinical diagnoses of cancer.

An Expanded Surface-Enhanced Raman Scattering Tags Library by Combinatorial Encapsulation of Reporter Molecules in Metal Nanoshells

Raman-encoded gold nanoparticles (NPs) have been widely employed as photostable multifunctional probes for sensing, bioimaging, multiplex diagnostics, and surface-enhanced Raman scattering (SERS)-guided tumor therapy. We report a strategy toward obtaining a particularly large library of Au nanocapsules encoded with Raman codes defined by the combination of different thiol-free Raman reporters, encapsulated at defined molar ratios. The fabrication of SERS tags with tailored size and predefined codes is based on the in situ incorporation of Raman reporter molecules inside Au nanocapsules during their formation via galvanic replacement coupled to seeded growth on Ag NPs. The hole-free closed-shell structure of the nanocapsules is confirmed by electron tomography. The unusually wide encoding possibilities of the obtained SERS tags are investigated by means of either wavenumber-based encoding or Raman frequency combined with signal intensity, leading to an outstanding performance as exemplified by 26 and 54 different codes, respectively. We additionally demonstrate that encoded nanocapsules can be readily bioconjugated with antibodies for applications such as SERS-based targeted cell imaging and phenotyping.

Silica-Coated, Waxberry-like Surface-Enhanced Raman Resonant Scattering Tag-Pair with Near-Infrared Raman Dye Encoding: Toward In Vivo Duplexing Detection

Surface-enhanced Raman resonant scattering (SERRS) tags encoded with near-infrared (NIR) Raman reporters showed great potential for in vivo detection owing to their ultrasensitivity. However, in vivo signal stability of such tags is a remaining problem due to the lack of suitable silica coating method because the weakly adsorbed NIR reporters tend to detach from traditional gold nanosubstrates in the ethanol-rich and high pH conditions, which are commonly used for silica coating. Herein, we propose a silica coating method for NIR SERRS tags by using waxberry-like gold nanoparticles (NPs) as substrates. The lipid bilayer of the NPs played a crucial role in the coating, which can encapsulate the NIR Raman reporter via hydrophobic interactions and prevent the interference from a harsh medium. Thus, the silica-coated tags well preserved ultrasensitivity of bare tags and simultaneously gained satisfactory signal stability in vivo. Moreover, the coating method is compatible for the encapsulation of a variety of thiol group-free NIR reporters (as exemplified by DTTC, Cy7, IR792, and DIR), relying on which a tag-pair with distinguishable peaks can be screened (labeling with DTTC and Cy7, respectively). In vivo duplexing detection revealed that the tag-pair-labeled liposome was cleared faster in the liver than polydopamine NPs within one mouse. The developed method paves an easy way for gaining high-quality SERRS tags and will promote their in vivo multiplex analysis and diagnostics applications.

Smart materials for point-of-care testing: From sample extraction to analyte sensing and readout signal generator

The last decade has seen a surge of technical developments in the field on point-of-care testing (POCT). While these developments are extremely diverse, the common aim is to implement improved methods for quick, reliable and inexpensive diagnosis of patients within the clinical setting. While examples of successful introduction and use of POCT techniques are growing, further developments are still necessary to create POCT devices with better portability, usability and performance. Advances in smart materials emerge as potentially valuable know-hows to provide a competitive edge to the development of next generation POCT devices. This review describes the key advantages of adopting smart material-based technologies at different analytical stages of a POCT platform. Under these analytical stages which involves sample pre-treatment, analyte sensing and readout signal generator, several concepts and approaches from contemporary research work in using smart material-based technologies will be the major focus in this review. Lastly, challenges and potential outlook in implementing materials technologies from the application point of view for POCT will be discussed.

Liposomal Delivery of Mycophenolic Acid With Quercetin for Improved Breast Cancer Therapy in SD Rats

The present study explores the influence of mycophenolic acid (MPA) in combination therapy with quercetin (QC) (impeding MPA metabolic rate) delivered using the liposomal nanoparticles (LNPs). Mycophenolic acid liposome nanoparticles (MPA-LNPs) and quercetin liposome nanoparticles (QC-LNPs) were individually prepared and comprehensively characterized. The size of prepared MPA-LNPs and QC-LNPs were found to be 183 ± 13 and 157 ± 09.8, respectively. The in vitro studies revealed the higher cellular uptake and cytotoxicity of combined therapy (MPA-LNPs + QC-LNPs) compared to individual ones. Moreover pharmacokinetics studies in female SD-rat shown higher T 1 / 2 value (1.94 fold) of combined therapy compared to MPA. Furthermore, in vivo anticancer activity in combination of MPA-LNPs and QC-LNPs was also significantly higher related to other treatments groups. The combination therapy of liposomes revealed the new therapeutic approach for the treatment of breast cancer.

Effects of lipid membrane composition on the distribution of biocidal guanidine oligomer with solid supported lipid membranes

Polyhexamethylene guanidine (PHMG) is a cationic antimicrobial oligomer that has been used prevalently over the past few decades. However, due to the lack of inhalation toxicity assessment of PHMG, it has caused severe health damage, including fatal lung fibrosis, after being used as one of the major active ingredients of humidifier disinfectants in Korea. Because the first step of the entry of PHMG into airway is its association with cell membranes, the distribution of PHMG between lipid membranes and water is very important to know the depositional flux in the respiratory systems and related toxic mechanisms. We developed a quantitative method to determine the distribution constant (K_lipw) of PHMG between solid supported lipid membranes and water and evaluated the effects of lipid membrane compositions on the K_lipw of PHMG. PHMG accumulated into anionic lipid membranes rapidly compared to into cationic or zwitterionic lipid membranes, suggesting fast adsorption of PHMG onto anionic lipid head groups. K_lipw values with anionic/zwitterionic lipid mixtures were higher than K_lipw values with anionic lipids only, potentially due to the later phase separation after preferential interaction between PHMG and anionic lipids in lipid mixtures. In addition, K_lipw values increased with increasing single acyl chain lipid content in unsaturated lipids and decreasing cholesterol content. These results imply that changes in lipid spontaneous curvature and lipid bilayer packing density also affect the membrane distribution of PHMG.

This study experimentally determined the K_lipw of PHMG and assessed the effects of lipid membrane composition on K_lipw values.

Synthesis of Monolayer Gold Nanorings Sandwich Film and Its Higher Surface-Enhanced Raman Scattering Intensity

Most previous studies relating to surface-enhanced Raman spectroscopy (SERS) signal enhancement were focused on the interaction between the light and the substrate in the x-y axis. 3D SERS substrates reported in the most of previous papers could contribute partial SERS enhancement via z axis, but the increases of the surface area were the main target for those reports. However, the z axis is also useful in achieving improved SERS intensity. In this work, hot spots along the z axis were specifically created in a sandwich nanofilm. Sandwich nanofilms were prepared with self-assembly and Langmuir-Blodgett techniques, and comprised of monolayer Au nanorings sandwiched between bottom Ag mirror and top Ag cover films. Monolayer Au nanorings were formed by self-assembly at the interface of water and hexane, followed by Langmuir-Blodgett transfer to a substrate with sputtered Ag mirror film. Their hollow property allows the light transmitted through a cover film. The use of a Ag cover layer of tens nanometers in thickness was critical, which allowed light access to the middle Au nanorings and the bottom Ag mirror, resulting in more plasmonic resonance and coupling along perpendicular interfaces (z-axis). The as-designed sandwich nanofilms could achieve an overall ~8 times SERS signals amplification compared to only the Au nanorings layer, which was principally attributed to enhanced electromagnetic fields along the created z-axis. Theoretical simulations based on finite-difference time-domain (FDTD) method showed consistent results with the experimental ones. This study points out a new direction to enhance the SERS intensity by involving more hot spots in z-axis in a designer nanostructure for high-performance molecular recognition and detection.

Gold Nanorod Array-Bridged Internal-Standard SERS Tags: From Ultrasensitivity to Multifunctionality

Bimetallic gold core-silver shell (Au@Ag) surface-enhanced Raman scattering (SERS) tags draw broad interest in the fields of biological and environmental analysis. In reported tags, silver coating tended to smooth the surface and merge the original hotspot of Au cores, which was disadvantageous to signal enhancement from the aspect of surface topography. Herein, we developed gold nanorod (AuNR)-bridged Au@Ag SERS tags with uniform three-dimensional (3D) topography for the first time. This unique structure was achieved by selecting waxberry-like Au nanoparticles (NPs) as cores, which were capped by vertically oriented AuNR arrays. Upon selective surface blocking with thiol-ligands, Ag NPs were controlled to anisotropically grow on the tips of the AuNRs, producing high-density homo- (Ag-Ag) and hetero- (Au-Ag) hotspots in a single NP. The 3D hotspots rendered this NP extraordinary SERS enhancement ability (an analytical enhancement factor of 3.4 × 10⁶) 30 times higher than the counterpart with a smooth surface, realizing signal detection from a single NP. More importantly, multiplexing signals ("blank" or multiplex "internal standard") can be achieved by simply changing thiol-ligands, as exemplified in the synthesis of NPs with 8 signatures. Furthermore, the multifunctionality has been demonstrated in living cell/in vivo imaging, photothermal therapy, and SERS substrates for ratiometric quantitative analysis, relying on the inherent internal standard signal. The prepared Au@Ag NPs have great potential as standard tools in many SERS-related fields.

Ultrasensitive SERS detection of specific oligonucleotides based on Au@AgAg bimetallic nanorods

We synthesized a novel and sensitive Au/Ag bimetallic SERS-active nanotag, Au-Ag-Ag core-shell-shell nanorod (Au@AgAgNR). The Au@AgAgNR nanotag exhibited a strong SERS signal and was easily assembled from bilayer silver shells on an Au nanorod (AuNR) core with embedded Raman reporter molecules in the core-shell-shell gaps. The SERS activity of the nanotags was investigated with 2-mercaptopyridine (2-Mpy) as a Raman reporter, which could form pyridine/Ag⁺ coordination complexes to mediate the formation of silver shells. Specific enhancement of Raman signals was observed in the following order: AuNR < Au@AgNR < Au@AgAgNR. Then, Au@AgAgNR nanotags were coupled with magnetic beads (MBs) via specific DNA hybridization as a SERS sensor with a detection limit of 1 fM for a segment of the gene HPV-16. Factors affecting sensitivity and selectivity were investigated, including Raman dye concentration, silver nitrate dosage and the response to similar oligonucleotides. The proposed SERS sensor is expected to be a facile and sensitive method for specific gene detection.

Phase transfer-driven rapid and complete ligand exchange for molecular assembly of phospholipid bilayers on aqueous gold nanocrystals

A phase transfer-mediated ligand exchange method is developed for highly selective and rapid synthesis of colloidal phospholipid bilayer-coated gold nanocrystals. The complete replacement of strongly bound surface ligands such as cetyltrimethylammonium bromide (CTAB) and citrate by phospholipid bilayer can be quickly achieved by water-chloroform phase transfer.

Ultra-small bimetallic iron–palladium (FePd) nanoparticle loaded macrophages for targeted tumor photothermal therapy in NIR-II biowindows and magnetic resonance imaging

Nanoparticles working in the NIR-II biowindows possess larger maximum permissible exposure (MPE) and desirable penetration depth to the laser. However, most NIR-II responsive nanomaterials lack tumor targeting and Magnetic Resonance Imaging (MRI) ability. This greatly limits their applications. This study reported ultra-small bimetallic iron–palladium (FePd) nanoparticle loaded macrophages for targeted tumor photothermal therapy in NIR-II biowindows and magnetic resonance imaging. The crystal phase, morphology, absorption spectrum and photothermal performance of the synthesized samples were systematically characterized. The effects of photothermal therapy and nuclear magnetic imaging (MRI) were studied both in vitro and in vivo. Since FePd nanoparticles have both iron and palladium elements, it had a good MRI imaging capability and high photothermal conversion efficiency (36.7%). After binding to macrophages, FePd nanoparticles@macrophages (FePd@M) showed a good tumor targeting ability and were used for targeting NIR-II photothermal therapy and MRI imaging of tumors. The results of photothermal treatment showed that the tumor volume decreased by 90% compared to the control group, and no significant organ toxicity was observed. The results of MRI imaging showed that the FePd@M has the best imaging effect. The nanoparticles with the excellent NIR-II PTT ability and MRI effect have overcome the problem of tumor targeting and avoid the rapid removal of ultra-small nanoparticles. The FePd@M delivery system provides new ideas for material construction in the NIR-II region and has great clinical application potential.

Nanoparticles working in the NIR-II biowindows possess larger maximum permissible exposure (MPE) and desirable penetration depth to the laser.

Nanomaterial-based SERS sensing technology for biomedical application

Over the past few years, nanomaterial-based surface-enhanced Raman scattering (SERS) detection has emerged as a new exciting field in which theoretical and experimental studies of the structure and function of nanomaterials have become a focus.

Lipid Bilayer-Enabled Synthesis of Waxberry-like Core-Fluidic Satellite Nanoparticles: Toward Ultrasensitive Surface-Enhanced Raman Scattering Tags for Bioimaging

Herein, we presented waxberry-like core-satellite (C-S) nanoparticles (NPs) prepared by an in situ growth of satellite gold NPs on spherical phospholipid bilayer-coated gold cores. The fluidic lipid bilayer cross-linker was reported for the first time, which imparted several novel morphological and optical properties to the C-S NPs. First, it regulated the anisotropic growth of the satellite NPs into vertically oriented nanorods on the core NP surface. Thus, an interesting waxberry-like nanostructure could be obtained, which was different from the conventional raspberry-like C-S structures decorated with spherical satellite NPs. Second, the satellite NPs were "soft-landed" on the lipid bilayer and could move on the core NP surface under certain conditions. The movement induced tunable plasmonic features in the C-S NPs. Furthermore, the fluidic lipid bilayer was capable of not only holding an abundance of reporter molecules but also delivering them to the hotspots at the junctions between the core and satellite NPs, which made the C-S NPs an excellent candidate for preparing ultrasensitive surface-enhanced Raman scattering (SERS) tags. The bioimaging capabilities of the C-S NP-based SERS tags were successfully demonstrated in living cells and mice. The developed SERS tags hold great potential for bioanalysis and medical diagnostics.

Gd2O3-doped silica @ Au nanoparticles for in vitro imaging cancer biomarkers using surface-enhanced Raman scattering

There has been an interest in developing multimodal approaches to combine the advantages of individual imaging modalities, as well as to compensate for respective weaknesses. We previously reported a composite nano-system composed of gadolinium-doped mesoporous silica nanoparticle and gold nanoparticle (Gd-Au NPs) as an efficient MRI contrast agent for in vivo cancer imaging. However, MRI lacks sensitivity and is unsuitable for in vitro cancer detection. Thus, here we performed a study to use the Gd-Au NPs for detection and imaging of a widely recognized human cancer biomarker, epidermal growth factor receptor (EGFR), in individual human cancer cells with surface-enhanced Raman scattering (SERS). The Gd-Au NPs were sequentially conjugated with a monoclonal antibody recognizing EGFR and a Raman reporter molecule, 4-meraptobenzoic acid (MBA), to generate a characteristic SERS signal at 1075cm^-1. By spatially mapping the SERS intensity at 1075cm^-1, cellular distribution of EGFR and its relocalization on the plasma membrane were measured in situ. In addition, the EGFR expression levels in three human cancer cell lines (S18, A431 and A549) were measured using this SERS probe, which were consistent with the comparable measurements using immunoblotting and immunofluorescence. Our SERS results show that functionalized Gd-Au NPs successfully targeted EGFR molecules in three human cancer cell lines and monitored changes in single cell EGFR distribution in situ, demonstrating its potential to study cell activity under physiological conditions. This SERS study, combined with our previous MRI study, suggests the Gd-Au nanocomposite is a promising candidate contrast agent for multimodal cancer imaging.

Electrospun Nanofibers Made of Silver Nanoparticles, Cellulose Nanocrystals, and Polyacrylonitrile as Substrates for Surface-Enhanced Raman Scattering

Nanofibers with excellent activities in surface-enhanced Raman scattering (SERS) were developed through electrospinning precursor suspensions consisting of polyacrylonitrile (PAN), silver nanoparticles (AgNPs), silicon nanoparticles (SiNPs), and cellulose nanocrystals (CNCs). Rheology of the precursor suspensions, and morphology, thermal properties, chemical structures, and SERS sensitivity of the nanofibers were investigated. The electrospun nanofibers showed uniform diameters with a smooth surface. Hydrofluoric (HF) acid treatment of the PAN/CNC/Ag composite nanofibers (defined as p-PAN/CNC/Ag) led to rougher fiber surfaces with certain pores and increased mean fiber diameters. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) results confirmed the existence of AgNPs that were formed during heat and HF acid treatment processes. In addition, thermal stability of the electrospun nanofibers increased due to the incorporation of CNCs and AgNPs. The p-PAN/CNC/Ag nanofibers were used as a SERS substrate to detect p-aminothiophenol (p-ATP) probe molecule. The results show that this substrate exhibited high sensitivity for the p-ATP probe detection.