Liquid Interfacial Gating of Superhydrophobic Plasmonic Metal-Organic Frameworks for Three-in-One Separation, Enrichment, and Recognition in Bacterial Quorum Sensing.

Poor adsorption properties of nonadsorbing targets and competing adsorption of nontargets at a liquid interface always hamper the development of interface sensing techniques. There is a need to fabricate materials that are applicable to various interface assemblies and, meanwhile, could be employed as interfacial gating to improve the performance of interface sensing by separating, enriching, and recognizing targets at the liquid interface. Here, superhydrophobic zeolite imidazole frameworks-8@gold nanoparticles-1H,1H,2H,2H-perfluorodecanethiol (ZIF-8@GNPs-PFDT) with a static water contact angle (WCA) of 155° was constructed via electrostatic self-assembly and surface graft modification. The plasmonic metal-organic framework (PMOF) nanohybrid realized all-purpose self-assembly at air/liquid and liquid/liquid interfaces and also facilely assembled on the surface of liquid droplets, hydrogels, and foams. The self-assembled porous materials displayed the capability for separating, enriching, and recognizing analytes at various oil/water interfaces and thus could be used to adsorb nonadsorbing targets and block the competing adsorption of nontargets. The self-assembled ZIF-8@GNPs-PFDT structures were employed as a three-in-one interfacial gating to endow the excellent surface-enhanced Raman scattering (SERS) sensing capability and has become a promising tool for dye molecular analysis, oil/water separation, organic phase identification, and in situ cultivation and monitoring of bacterial quorum sensing (QS).

Acoustofluidic one-step production of plasmonic Ag nanoparticles for portable paper-based ultrasensitive SERS detection of bactericides.

SERS measurements for monitoring bactericides in dairy products are highly desired for food safety problems. However, the complicated preparation process of SERS substrates greatly impedes the promotion of SERS. Here, we propose acoustofluidic one-step synthesis of Ag nanoparticles on paper substrates for SERS detection. Our method is economical, fast, simple, and eco-friendly. We adopted laser cutting to cut out appropriate paper shapes, and aldehydes were simultaneously produced at the cutting edge in the pyrolysis of cellulose by laser which were leveraged as the reducing reagent. In the synthesis, only 5 µL of Ag precursor was added to complete the reaction, and no reducing agent was used. Our recently developed acoustofluidic device was employed to intensely mix Ag+ ions and aldehydes and spread the reduced Ag nanoparticles over the substrate. The SERS substrate was fabricated in 1 step and 3 min. The standard R6G solution measurement demonstrated the excellent signal and prominent uniformity of the fabricated SERS substrates. SERS detection of the safe concentration of three bactericides, including tetracycline hydrochloride, thiabendazole, and malachite green, from food samples can be achieved using fabricated substrates. We take the least cost, time, reagents, and steps to fabricate the SERS substrate with satisfying performance. Our work has an extraodinary meaning for the green preparation and large-scale application of SERS.

Flexible microfluidic co-recognition coupled with magnetic enrichment and silent SERS sensing for simultaneous analysis of bacteria in food.

Food safety represents a critical global public health issue, with safety challenges posed by foodborne pathogens garnering extensive attention. Therefore, we introduce a co-recognition, enrichment and sensing (CES) all-in-one strategy for analysis of bacteria with low background and high specificity. This method employs antimicrobial peptide (AMP) functionalized magnetic nanoparticles (MNPs) to enrich bacteria and uses aptamer@Au@PBA (KxMFe(CN)6 (M = Pb and Ni)) NPs as silent SERS tags. When both S. aureus and E. coli O157:H7 are present, the silent SERS probes could specifically label the target bacteria, forming a sandwich-like structure. This binding induces silent Raman shifts (2139 cm-1 and 2197 cm-1), enabling quantification of two bacteria. Coupling with the modular flexible microfluidics and magnetic control slider device, this platform facilitates rapid switching between magnetic loading and elution. The CES SERS method demonstrated linear relationships for both S. aureus and E. coli O157:H7 at 50-1600 cfu mL-1, with detection limits of 14 and 18 cfu mL-1, respectively. The method achieved recovery rates of 85.6-112% and relative standard deviations of 1.5-8.6%. Validation using the ELISA method revealed relative errors between -7.5 and 4.3%. The CES approach has potential applications in food safety, environmental monitoring, and biomedical diagnosis.

Macrocyclic Diacetylene / Sulfonate Fluorophore Hierarchical Multifunctional Nanotoroids.

Functional supramolecular materials exhibit important features including structural versatility and versatile applications. Here, this study reports the construction of unique hierarchically organized nanotoroids exhibiting fluorescence, photocatalytic, and sensing properties. The nanotoroids comprise of macrocyclic diacetylenes (MCDA) and 8-anilino-1-naphthalene sulfonate (ANS), a negatively charged aromatic fluorescent dye. This study shows that the hierarchical structure of the nanotoroids consist of MCDA nanofibers formed by stacked diacetylene monomers as the basic units, which are further bent and aligned into toroidal organization by electrostatic and hydrophobic interactions with the ANS molecules. The amine moieties on the nanotoroids surface are employed for deposition of gold nanostructures - Au nanoparticles or Au nanosheets - which constitute effective platforms for photocatalysis and surface enhanced Raman scattering (SERS)-based sensing.

Ag@AuNP-Functionalized Capillary-Based SERS Sensing Platform for Interference-Free Detection of Glucose in Urine Using SERS Tags with Built-In Nitrile Signal.

A Ag@AuNP-functionalized capillary-based surface-enhanced Raman scattering (SERS) sensing platform for the interference-free detection of glucose using SERS tags with a built-in nitrile signal has been proposed in this work. Capillary-based SERS capture substrates were prepared by connecting 4-mercaptophenylboronic acid (MBA) to the surface of the Ag@AuNP layer anchored on the inner wall of the capillaries. The SERS tags with a built-in interference-free signal could then be fixed onto the Ag@AuNP layer of the capillary-based capture substrate based on the distinguished feature of glucose, which can form a bidentate glucose-boronic complex. Thus, many "hot spots" were formed, which produced an improved SERS signal. The quantitative analysis of glucose levels was realized using the interference-free SERS intensity of nitrile at 2222 cm-1, with a detection limit of about 0.059 mM. Additionally, the capillary-based disposable SERS sensing platform was successfully employed to detect glucose in artificial urine, and the new strategy has great potential to be further applied in the diagnosis and control of diabetes.

A Direct Immunoassay Based on Surface-Enhanced Spectroscopy Using AuNP/PS-b-P2VP Nanocomposites.

A biosensor was developed for directly detecting human immunoglobulin G (IgG) and adenosine triphosphate (ATP) based on stable and reproducible gold nanoparticles/polystyrene-b-poly(2-vinylpyridine) (AuNP/PS-b-P2VP) nanocomposites. The substrates were functionalized with carboxylic acid groups for the covalent binding of anti-IgG and anti-ATP and the detection of IgG and ATP (1 to 150 µg/mL). SEM images of the nanocomposite show 17 ± 2 nm AuNP clusters adsorbed over a continuous porous PS-b-P2VP thin film. UV-VIS and SERS were used to characterize each step of the substrate functionalization and the specific interaction between anti-IgG and the targeted IgG analyte. The UV-VIS results show a redshift of the LSPR band as the AuNP surface was functionalized and SERS measurements showed consistent changes in the spectral features. Principal component analysis (PCA) was used to discriminate between samples before and after the affinity tests. Moreover, the designed biosensor proved to be sensitive to different concentrations of IgG with a limit-of-detection (LOD) down to 1 µg/mL. Moreover, the selectivity to IgG was confirmed using standard solutions of IgM as a control. Finally, ATP direct immunoassay (LOD = 1 µg/mL) has demonstrated that this nanocomposite platform can be used to detect different types of biomolecules after proper functionalization.

Peroxidase-like Nanozymes for Point-of-Care SERS Sensing and Wound Healing.

The emergence of nanozymes provides a potential method for combating multidrug-resistant bacteria resulted from the abuse of antibiotics. However, in nanozyme-catalyzed systems, few studies have addressed the actual hydrogen peroxide (H2O2) level involved in sterilization. Herein, we designed a high-efficiency peroxidase-mimicking nanozyme with surface-enhanced Raman scattering (SERS) property by assembling gold nanoparticles on single-layer Cu2+-C3N4 (AuNP-Cu2+-C3N4). The nanozyme effectively converts the low-active Raman reporter 3,3',5,5'-tetramethylbenzidine (TMB) into its oxidized form with H2O2, resulting in SERS signal changes, thereby achieving highly sensitive quantification of H2O2 with limit of detection as low as 0.60 µM. More importantly, the nanozyme can specifically catalyze H2O2 into antibacterial hydroxyl radicals. In vitro and in vivo evaluations demonstrate the remarkable antibacterial efficacy of the nanozyme/H2O2 combination against Staphylococcus aureus (up to 99.9%), which could promote wound healing in mice and allow point-of-care monitoring the amount of H2O2 participated in effective sterilization. This study not only displays great potential in combining multiple functionalities of nanomaterials for versatile bioassays but also provides a promising approach to design nanozymes for biomedical and catalytic applications.

Dual-source powered nanomotor with integrated functions for cancer photo-theranostics.

While the miniaturization and motility of artificial nanomotors made them popular tools for exploring novel and innovative biomedical cancer treatment strategies, the integration of multiple functions on the small motor bodies is key to achieve further progress but remains unresolved. Here, we propose a dual-source powered Janus nanomotor whose composition integrates multiple photo-theranostic functions such as surface-enhanced Raman scattering (SERS) sensing, fluorescence imaging/photoacoustic imaging (PAI), photodynamic therapy (PDT), and photothermal therapy (PTT). This nanomotor can be fabricated by sputtering a thin gold layer onto one side of mesoporous silica (mSiO2) combined with surface modification by photo-sensitizer, Raman reporter, and catalase. Upon illumination with 808 nm near-infrared light, the half-coated gold nanoshell serves as PAI/PTT agent, and by upconverting NIR to visible light, the pre-loaded photosensitizer can be excited by the upconverted light of UCNPs to convert the dissolved oxygen (O2) into reactive oxygen species for efficient PDT. Furthermore, ratiometric SERS signal can be captured to quantitatively detect the tumor marker, H2O2, in cellular microenvironments. The immobilized catalase as a nano-engine can catalyze endogenous H2O2 to O2. This function not only improves the hypoxic tumor microenvironment and therefore enhances PDT efficiency, but also provides a thrust force for deep penetration. As a proof of concept for the in vivo trial we performed cancer photo-theranostics where our nanomotors successfully treated a mouse breast tumor in a subcutaneous tumor model. The results are promising and encourage the use of an integrated nanomotor platform that could be further developed into a photo-theranostic agent for superficial cancer treatment.

Large-Area Nanosphere Self-Assembly Monolayers for Periodic Surface Nanostructures with Ultrasensitive and Spatially Uniform SERS Sensing.

Colloidal lithography provides a rapid and low-cost approach to construct 2D periodic surface nanostructures. However, an impressive demonstration to prepare large-area colloidal template is still missing. Here, a high-efficient and flexible technique is proposed to fabricate self-assembly monolayers consisting of orderly-packed polystyrene spheres at air/water interface via ultrasonic spray. This "non-contact" technique exhibits great advantages in terms of scalability and adaptability due to its renitent interface dynamic balance. More importantly, this technique is not only competent for self-assembly of single-sized polystyrene spheres, but also for binary polystyrene spheres, completely reversing the current hard situation of preparing large-area self-assembly monolayers. As a representative application, hexagonal-packed silver-coated silicon nanorods array (Si-NRs@Ag) is developed as an ultrasensitive surface-enhanced Raman scattering (SERS) substrate with very low limit-of-detection for selective detection of explosive 2,4,6-trinitrotoluene down to femtomolar (10-14 m) range. The periodicity and orderliness of the array allow hot spots to be designed and constructed in a homogeneous fashion, resulting in an incomparable uniformity and reproducibility of Raman signals. All these excellent properties come from the Si-NRs@Ag substrate based on the ordered structure, open surface, and wide-range electric field, providing a robust, consistent, and tunable platform for molecule trapping and SERS sensing for a wide range of organic molecules.

Preparation of Fe3O4-Ag Nanocomposites with Silver Petals for SERS Application.

The formation of silver nanopetal-Fe3O4 poly-nanocrystals assemblies and the use of the resulting hetero-nanostructures as active substrates for Surface Enhanced Raman Spectroscopy (SERS) application are here reported. In practice, about 180 nm sized polyol-made Fe3O4 spheres, constituted by 10 nm sized crystals, were functionalized by (3-aminopropyl)triethoxysilane (APTES) to become positively charged, which can then electrostatically interact with negatively charged silver seeds. Silver petals were formed by seed-mediated growth in presence of Ag+ cations and self-assembly, using L-ascorbic acid (L-AA) and polyvinyl pyrrolidone (PVP) as mid-reducing and stabilizing agents, respectively. The resulting plasmonic structure provides a rough surface with plenty of hot spots able to locally enhance significantly any applied electrical field. Additionally, they exhibited a high enough saturation magnetization with Ms = 9.7 emu g-1 to be reversibly collected by an external magnetic field, which shortened the detection time. The plasmonic property makes the engineered Fe3O4-Ag architectures particularly valuable for magnetically assisted ultra-sensitive SERS sensing. This was unambiguously established through the successful detection, in water, of traces, (down to 10-10 M) of Rhodamine 6G (R6G), at room temperature.

Mesoporous Nanostructures Encapsulated with Metallic Nanodots for Smart SERS Sensing.

In virtue of uniform mesopores and core-shell nanoarchitectures, metallic nanodot-encapsulated hollow mesoporous nanostructures have shown promising potential in various applications. However, their fabrication with versatile tunability of the encapsulated metallic content has been a challenge. Herein, we have prepared metallic nanodot-encapsulated hollow mesoporous silica nanoparticles (M-HMSNPs) with adjustable inner metallic components. The sacrificial template of polystyrene (PS) nanoparticles precoated with metals (Au/Ag/Pt) is fully wrapped with mesoporous silica (mSiO2). The metallic nanodots are formed during the template removal process by calcination. The type and content of the encapsulated nanodots can be readily and precisely controlled by the initially deposited metallic layers. We demonstrate the application of the gold (Au) nanodot-loaded HMSNPs (denoted Au-HMSNPs) as smart surface-enhanced Raman spectroscopy (SERS) probes, which can screen between big molecules and small analytes. With the aid of a Raman reporter, the SERS probe can successfully quantify H2O2, which is used to distinguish cancer cells in vitro. Further integrated with enzymes, the SERS chips of specificity are prepared and used to detect corresponding substrates of glucose and uric acid, responsively. Besides SERS sensing, the current strategy can inspire future development of many other M-HMSNPs for various applications such as catalysis, energy storage, theranostics, etc.

Integrating Plasmonic Supercrystals in Microfluidics for Ultrasensitive, Label-Free, and Selective Surface-Enhanced Raman Spectroscopy Detection.

Surface-enhanced Raman spectroscopy (SERS) microfluidic chips for label-free and ultrasensitive detection are fabricated by integrating a plasmonic supercrystal within microfluidic channels. This plasmonic platform allows the uniform infiltration of the analytes within the supercrystal, reaching the so-called hot spots. Moreover, state-of-the-art simulations performed using large-scale supercrystal models demonstrate that the excellent SERS response is due to the hierarchical nanoparticle organization, the interparticle separation (IPS), and the presence of supercrystal defects. Proof-of-concept experiments confirm the outstanding performance of the microfluidic chips for the ultradetection of (bio)molecules with no metal affinity. In fact, a limit of detection (LOD) as low as 10-19 M was reached for crystal violet. The SERS microfluidic chips show excellent sensitivity in the direct analysis of pyocyanin secreted by Pseudomonas aeruginosa grown in a liquid culture medium. Finally, the further integration of a silica-based column in the plasmonic microchip provides charge-selective SERS capabilities as demonstrated for a mixture of positively and negatively charged molecules.

Synthesis of silver nanoplates on electrospun fibers via tollens reaction for SERS sensing of pesticide residues.

Silver nanoplates were for the first time synthesized on electrospun chitosan/polyethylene oxide (CS/PEO) fibers via tollens reaction. Ag nanoplates/CS/PEO fibers were used as the SERS-active substrates for quantitative evaluation of 2-naphthylthiol, with an enhancement factor (1.41 ± 0.07) × 106. The SERS-active substrates are flexible, stable, and easy for transportion and preservation, and act as the SERS platform for sensitive detection of the target. Thiram and thiabendazole as the representatives of pesticide residues were identified and detected by the Ag nanoplates/CS/PEO fibers, exhibiting linear response ranges from 10-11 to 10-7 M with a detection limit of 10-11 M. The Ag nanoplates/CS/PEO fibers meet the requirement of thiram detection in practical samples, such as apple, pear, tomato, and cucumber juices. The strategy revealed the feasibility of fabrication of Ag nanoplates on electrospun fibers via tollens reaction and SERS sensing of pesticides in real samples. Ag nanoplates/CS/PEO fibers were fabricated by tollens reaction and electrospinning for SERS sensing of pesticide residues with high sensitivity.

Acoustofluidics-Assisted Engineering of Multifunctional Three-Dimensional Zinc Oxide Nanoarrays.

The integration of acoustics and microfluidics (termed acoustofluidics) presents a frontier in the engineering of functional micro-/nanomaterials. Acoustofluidic techniques enable active and precise spatiotemporal control of matter, providing great potential for the design of advanced nanosystems with tunable material properties. In this work, we introduce an acoustofluidic approach for engineering multifunctional three-dimensional nanostructure arrays and demonstrate their potential in enrichment and biosensing applications. In particular, our acoustofluidic device integrates an acoustic transducer with a sharp-edge-based acoustofluidic reactor that enables uniform patterning of zinc oxide (ZnO) nanoarrays with customizable lengths, densities, diameters, and other properties. The resulting ZnO nanoarray-coated glass capillaries can rapidly and efficiently capture and enrich biomolecules with sizes ranging from a few nanometers to several hundred nanometers. In order to enable the detection of these biomolecules, silver (Ag) nanoparticles are deposited onto the ZnO nanoarrays, and the integrated ZnO-Ag capillary device functions as a label-free plasmonic biosensing system for surface-enhanced Raman spectroscopy (SERS) based detection of exosomes, DNA oligonucleotides, and E. coli bacteria. The optical sensing enhancement of ZnO-Ag capillary is further validated through finite-difference time-domain (FDTD) simulations. These findings not only provide insights into the engineering of functional micro/nanomaterials using acoustofluidics but also shed light onto the development of portable microanalytical devices for point-of-care applications.

Ta@Ag Porous Array with High Stability and Biocompatibility for SERS Sensing of Bacteria.

The reliable sensing of bacteria by surface-enhanced Raman scattering (SERS) technology necessitates a rational design of a substrate with high sensitivity, stability, and minimal invasion. Hence, a bimetallic Ta@Ag film with a porous array is developed by the magnetron sputtering technique and the structure could be controlled by a Ta dopant. A porous array connected by ligaments with compact granular nanoprotrusions is a fascinating substrate for SERS sensing. It makes steady SERS signals even in harsh chemical environments due to its high structural and chemical stability. The configuration of binary Ta@Ag has higher surface free energy than that of pure Ag, and the strong bactericidal activity of Ag is suppressed efficiently. Using E. coli as a model pathogen, the Ta@Ag porous film could maintain the long-term survival rate of E. coli up to 95% and a limit of SERS detection of E. coli down to 102 CFU/mL, which is measured by the standard colony-counting method. In sum, this work provides a promising strategy to fabricate a corrosion-resistant and biocompatible bimetallic Ta@Ag film with a porous array for the SERS sensing of microbial cells.

Template-Confined Site-Specific Electrodeposition of Nanoparticle Cluster-in-Bowl Arrays as Surface Enhanced Raman Spectroscopy Substrates.

Nanoparticle clusters have important applications in plasmonics and optical sensing fields. Various methods have been used to construct nanoparticle clusters, represented by assembling preprepared nanoparticles using DNA. However, preparation of nanoparticle clusters using a one-step method is still challenging. Herein, by using prepatterned microscale bowls as individual reaction containers, clusters of Au nanoparticles with a homogeneous structure are electrodeposited at the bottom of each bowl. The structure of the nanoparticle clusters can be simply manipulated by varying electrodeposition parameters. After coating these Au nanoparticle cluster-in-bowl arrays with a thin layer of Ag film, they can be used as surface enhanced Raman spectroscopy (SERS) substrates with an SERS enhancement factor of ∼108. Importantly, the concave bowl structures can facilitate delivery of the analytes into the crevices between the bowls and the nanoparticle clusters where SERS "hot spots" (or sensitive sites) are located. The crevices with a gradually changed gap distance between the concave bowl structure and the nanoparticle clusters are excellent traps for catching and SERS sensing of biospecies with varied sizes (e.g., viruses and proteins). We demonstrated sensitive SERS detection of viruses and proteins using the nanoparticle-cluster-in-bowl SERS substrates. This technique has the ability to control the resulting structure at specific locations with electrodeposited materials, which enables new opportunities for assembling complex surface patterns with diverse applications in optical and plasmonic fields.

Pillar[5]arene-Based Supramolecular Plasmonic Thin Films for Label-Free, Quantitative and Multiplex SERS Detection.

Novel plasmonic thin films based on electrostatic layer-by-layer (LbL) deposition of citrate-stabilized Au nanoparticles (NPs) and ammonium pillar[5]arene (AP[5]A) have been developed. The supramolecular-induced LbL assembly of the plasmonic nanoparticles yields the formation of controlled hot spots with uniform interparticle distances. At the same time, this strategy allows modulating the density and dimensions of the Au aggregates, and therefore the optical response, on the thin film with the number of AuNP-AP[5]A deposition cycles. Characterization of the AuNP-AP[5]A hybrid platforms as a function of the deposition cycles was performed by means of visible-NIR absorption spectroscopy, and scanning electron and atomic force microscopies, showing larger aggregates with the number of cycles. Additionally, the surface enhanced Raman scattering efficiency of the resulting AuNP-AP[5]A thin films has been investigated for three different laser excitations (633, 785, and 830 nm) and using pyrene as Raman probe. The best performance was shown by the AuNP-AP[5]A film obtained with two deposition cycles ((AuNP-AP[5]A)2) when excited with a 785 laser line. The optical response and SERS efficiency of the thin films were also simulated using the M3 solver and employing computer aided design models built based on SEM images of the different films. The use of host molecules as building blocks to fabricate (AuNP-AP[5]A)2) films has enabled the ultradetection, in liquid and gas phase, of low molecular weight polyaromatic hydrocarbons, PAHs, with no affinity for gold but toward the hydrophobic AP[5]A cavity. Besides, these plasmonic platforms allowed achieving quantitative detection within certain concentration regimes. Finally, the multiplex sensing capabilities of the AuNP-AP[5]A)2 were evaluated for their ability to detect in liquid and gas phase three different PAHs.

Composite Sensor Particles for Tuned SERS Sensing: Microfluidic Synthesis, Properties and Applications.

Surface-enhanced Raman scattering (SERS) is a promising platform for particle-based sensor signaling, and droplet-based microfluidic systems are particularly advantageous for control of the size and composition of micro- and nanoparticles. For controlled sensing application, a high homogeneity of the sensor particles is a key requirement, and the particles with functional properties demand for the preparation in a minimum number of synthesis steps. Frequently used coflow and flow focusing arrangements, however, produce the microparticles of only larger size. To address such concern for downscaling of particle size, which is crucial for strong sensing outcome, we have used a peculiar micro cross-flow arrangement here for generating the polymer microparticles of broad size range between 30 and 600 µm along with in situ embedded silver nanoparticles. Embedded silver acts as nuclei for additional silver enforcement via silver-catalyzed silver deposition in order to realize the composite microparticles for SERS sensing. The homogeneous size and spatial distribution of silver nanoparticles inside the matrix and enforcement over the surface together with controlled pore size provides a high and homogeneous loading of polymer composite sensor. Moreover, different parameters such as analytes concentration and particles size have been studied here for SERS sensing application of biochemical molecules (amino acids and vitamins). Overall, the platform for size-tuned droplets generation, synthesis of composite microparticles, mechanism for synchronized photopolymerization-photoreduction, tuned silver enforcement, and the impacts of different analytes on differently composed microparticles are systematically investigated in this paper.