Aggregation Of Silver Nanoparticles Research Articles

Correlated Polarization Dependences between Surface-Enhanced Resonant Raman Scattering and Plasmon Resonance Elastic Scattering Showing Spectral Uncorrelation to Each Other

We investigated the origin of the identical polarization angle dependence between surface-enhanced resonant Raman scattering (SERRS) and plasmon resonance elastic scattering (PRES) for two types of single silver nanoparticle aggregates. The first type (Type I), in which the SERRS spectral envelopes are similar to the PRES spectra, shows the identical polarization dependence between the SERRS and PRES. The second type (Type II), in which the SERRS envelopes largely deviate from the PRES spectra, also exhibits identical polarization dependence. Scanning electron microscopy observations indicated that the aggregates were dimers. This unintuitive result was examined by calculating the electromagnetic enhancement by changing the morphology of the dimers. The calculations revealed that the Type I dimer generates SERRS directly by superradiant plasmons. The Type II dimer generates SERRS indirectly via subradiant plasmons, which receive light energy from superradiant plasmons. This indirect SERRS process clarifies that the interaction between the superradiant and subradiant plasmons results in an identical polarization dependence between SERRS and PRES for Type II dimers.

Preparation and Characterization of Silver Nanoparticles Using Rosemary and Olive Leaf Aqueous Extracts

Nano technology is single of the current technologies that are used in several playing field as well as agriculture, Nano-particles are produced in various ways, one of which is the biological method, which is one of the easy, fast, inexpensive and environmentally safe methods. This reference study deals with the latest studies on the manufacture of microorganisms and plant extracts, Biosynthesis of metallic nanoparticles using plant extracts. This study aims to use extracts of olive leaves and rosemary leaves as a biological agent to reduce silver nitrate to silver nanoparticles and capping solutions at pH 6.5 the color of the extracts changed from brown to dark green after adding silver nitrate solution indicating the formation of silver nanoparticles. These nano compounds were characterized using X-ray Diffraction, Atomic Force Microscopy and UV-Visible spectrophotometer. Silver nanoparticles were characterized using UV-visible radiation Spectral analysis which showed the highest peaks for olive leaf and rosemary extracts, respectively, at 450nm and 590nm, When examining the extracts of silver nanoparticles for olive leaves and rosemary leaves characterized using X-ray Diffraction a peak at 2θ= 40 appeared indicating the presence of silver nanoparticles, Finally, when diagnosing silver nanoparticles using atomic force electron technology The given microscopy (AFM) showed limited bandwidth high molecular assemblies of silver nanoparticles of olive leaf and rosemary leaf extract respectively (0-8.4) and (0-31) nm.

Large Optical Asymmetry in Silver Nanoparticle Assemblies Enabled by CH-π Interaction-Mediated Chirality Transfer.

Transfer of asymmetry from the molecular system to the other distinct system requires appropriate chemical interactions. Here, we show how the CH-π interaction, one of the weakest hydrogen bonds, can be applied to transfer the asymmetry from π-conjugated chiral molecules to the assemblies of plasmonic Ag nanoparticles, where the aliphatic chains of chiral molecules and the polystyrene chains grafted on Ag nanoparticles are served as the hydrogen donor and acceptor, respectively. The optical asymmetry g-factor of the chiral assemblies of plasmonic nanoparticles is strongly dependent on the molecular weight of the polystyrene ligand, the core structure of the molecule, and the aliphatic chain length of the chiral molecule. Importantly, we explore a molecular mixing strategy to enhance the asymmetry g-factor of chiral molecular assemblies, which consequently promotes the g-factor of chiral plasmonics efficiently, reaching a high value of ∼0.05 under optimal conditions. Overall, we rationalize the chirality transfer from chiral molecules to inorganic nanoparticles, providing the guidance for structural design of chiral nanocomposites with a high g-factor.

Detection of Cell-Derived Exosomes Via Surface-Enhanced Raman Scattering Using Aggregated Silver Nanoparticles.

Exosomes are small extracellular vesicles that contain RNA, lipids, and proteins and can act as cellular messengers, carrying information to cells and tissues in the body. Thus, sensitive, label-free, and multiplexed analysis of exosomes may help in early diagnosis of important diseases. Here, we describe the process of pretreatment of cell-derived exosomes, preparation of surface-enhanced Raman scattering (SERS) substrates, and label-free SERS detection of exosomes using sodium borohydride aggregators. This method can enable the observation of SERS signals of exosomes that are clear and stable and have a good signal-to-noise ratio.

Spectroscopic analyses of particle and energy aggregations at the interface of silver nanoparticles and fluorescent carbon nanodots.

We study the change in the surface electromagnetic field provided by photoexcited silver nanoparticles as the field is disturbed by fluorescent carbon nanodots. Fluorescent carbon nanodots with an appropriate quantity and quality of surface functional groups are used to mediate the aggregation of silver nanoparticles of matching size and shape to form available nano-size conical structures. Carbon nanodots in the composite absorb and transfer additional photoenergy to the silver surface, resulting in energy aggregation within the cone structure and enhancement of the electromagnetic field in proximity to the silver surface. This elevated energy state is manifested in the strengthening of the SERS signal of the analytical probe 4-aminophenyl disulfide and the mechanism involved is elucidated by additional molecular spectroscopy studies.

Ag-Doped Metal-Organic Frameworks' Heterostructure for Sonodynamic Therapy of Deep-Seated Cancer and Bacterial Infection.

Metal-organic frameworks (MOF) have attracted great potential in sonodynamic therapy (SDT) owing to large sonosensitizers' loading and fast reactive oxygen species' (ROS) diffusion; however, the low ligand-to-metal charge transfer efficiency sharply impairs the SDT effect. Herein, we report the design of MIL@Ag heterostructures with high electron-hole pairs separation efficiency and enhanced diverse ROS generation ability for deep-seated cancer treatment and bacterial infection. The MIL@Ag heterostructure is composed of Ti-based MOFs (named MIL), on which are in situ assembled silver nanoparticles (Ag NPs). The electrochemical experiments and density functional theory calculations verify that the introduction of Ag NPs can significantly improve the electron transfer efficiency and O2 adsorption capacity of MIL. Under ultrasound irradiation, the doped Ag NPs can trap the activated electrons from MIL to reduce surrounding O2 and produce superoxide radicals (•O2-), while the activated holes enable oxidizing H2O to produce hydroxyl radicals (•OH). Thus, they efficiently improve the therapeutic efficiency of SDT. MIL@Ag-PEG-mediated SDT implements A549 cancer cells' killing under a tissue barrier of 2 cm and eradicates the bacterial infection of Staphylococcus aureus, thus promoting wound healing. Therefore, MIL@Ag-PEG provides a promising strategy for augmenting SDT performance by rational heterostructure design of sonosensitizers.

Phosphoric Acid Induced Controllable Nanoparticle Aggregation for Ultrasensitive SERS Detection of Malondialdehyde in a Microfluidic Chip

Malondialdehyde (MDA), one of the most important products of lipid peroxidation, has been widely accepted as a biomarker to indicate food rancidity as well as the progress of some human diseases. However, ready detection of MDA with ultra-high sensitivity remains a challenge. In this work, a microfluidic surface-enhanced Raman scattering (SERS) sensing chip based on phosphoric acid induced nanoparticles aggregation was proposed for ultrasensitive MDA detection. The sensing chip was composed of an ultrafast microfluidic mixer, which efficiently transferred analytes to hot spots via the mixer assisted hot spots occupying (MAHSO) SERS strategy. Phosphoric acid, a reagent used in MDA detection, played the role of aggregator to induce aggregation of silver nanoparticles (Ag NPs); meanwhile, as fast as a few milliseconds mixing time effectively prevented over-aggregation of Ag NPs. Therefore, this process generated a uniform and dense SERS substrate with analyte molecules located in hot spots. As a result, the MDA SERS sensing chip possessed a limit of detection (LOD) lower than 3.3 × 10−11 M, high spot-to-spot uniformity with a relative standard deviation (RSD) of 9.0% and an excellent batch-to-batch reproducibility with a RSD of 3.9%. This method also demonstrated excellent specificity and reliability in real sample detection with recoveries of 90.4–109.8% in spiked tests.

Silver nanoparticles-glycine-functionalized graphene platform for ultra-sensitive determination of bergenin

Herein, an efficient method for in-situ assembly of silver (Ag) nanoparticles on glycine functionalized graphene (Gly-Gr) has been proposed, which only requires a simple one-step hydrothermal reaction. The microstructure of the material (Ag-Gly-Gr) was characterized by a series of methods, such as FT-IR, XRD, and TEM. For comparison, glycine functionalized graphene (Gly-Gr) was prepared by the same way without adding silver nitrate. The electrochemical sensor (Ag-Gly-Gr/GCE or Gly-Gr/GCE) was prepared by coating the glassy carbon electrode (GCE) surface with dispersive droplets of the related material. The outcomes of the electrochemical impedance test showed that the charge transfer resistance of Ag-Gly-Gr/GCE was less than that of Gly-Gr/GCE and GCE. Compared with the other two sensors, Ag-Gly-Gr/GCE showed a more sensitive response for bergenin. By studying the influence of the pH and sweep rate on the peak potential, the dynamics parameters were discussed to understand the electrochemical reaction mechanism of bergenin. The strategy for quantitative analysis of bergenin was further established at the working potential of 0.8 V (vs SCE). The peak current of bergenin displayed a linear dependence for concentration in 0.01–1 μM with a detection limit of 3.0 nM. Additionally, the analytical availability of Ag-Gly-Gr/GCE was demonstrated by determining bergenin in real-life samples.

Lamellar and Hexagonal Assemblies of PEG-Grafted Silver Nanoparticles: Implications for Plasmonics and Photonics

Lamellar and Hexagonal Assemblies of PEG-Grafted Silver Nanoparticles: Implications for Plasmonics and Photonics

Contribution to optimization and standardization of antibacterial assays with silver nanoparticles: the culture medium and their aggregation

The antimicrobial activity of silver nanoparticles is determined by their size and specific properties, as well as by the chemical composition of the exposure medium in which the nanoparticles are suspended. When the antibacterial tests are carried out in a culture medium, aggregation of the nanoparticles is produced, decreasing their effectiveness. This study proposes the addition of surfactants to the culture medium to prevent the aggregation of silver nanoparticles and optimizes the concentrations of these surfactants. The aggregation of silver nanoparticles was studied by dynamic light scattering (DLS) after dispersion in three liquid culture media (Mueller-Hinton (MH), Luria-Bertani (LB) and Brain Heart Infusion) in which four different surfactants (SDS, Triton X100, Tween 80 and CTAB) were added at concentrations of 0, 0.1, 0.5, 1, 1.5 and 2%. Results showed that, the optimal culture media to prevent aggregation of silver nanoparticles were MH and LB with higher concentrations of Tween 80 and Triton X100 surfactants; being MH + 2% of Tween 80 and MH + 1% Triton X100 the best combinations obtained because the results obtained were closest to the sizes of nanoparticles in ultrapure water. In addition, it has been verified that the optimal medium + surfactant combinations chosen did not affect the viability of Escherichia coli bacteria. Nanoparticle aggregation was not observed by single particle inductively coupled plasma mass spectrometry (SP-ICP-MS) when nanoparticles were incubated for long incubations periods (24 h) in the optimal medium chosen.

Silica-Gel Incorporated Biosynthesized-Silver Nanoparticles for Sustainable Antimicrobial Treatment of Brackish Water Aquaculture

Treatment of brackish water from pathogenic microbes is crucial for sustainable aquaculture production and preventing the spread of infectious diseases. However, the treatment of brackish water is still challenging due to the high salinity and the high antimicrobial resistance. Here, we exploit a facile and effective approach to synthesize silica gel embedded with silver nanoparticles (7–48 nm) for broad-spectrum antimicrobial activity. The incorporation of silver nanoparticles into silica gel (AgNPs@SG) is confirmed by flame atomic absorption spectrometry, X-ray diffraction, N2 physisorption, and transmission electron microscopy. The AgNPs@SG material exhibits wide-spectrum antimicrobial activity against the studied microorganisms (Pseudomonas aeruginosa, Escherichia coli, and Candida albicans) due to preventing the aggregation of silver nanoparticles and their effective contact with the microorganisms. Most importantly, the applicability of the synthesized AgNPs@SG for the microbial treatment of brackish water is investigated on different water samples collected from Manzala Lake. Remarkably, the amount of viable bacteria in the brackish water decreases by about 93% using AgNPs@SG material that not only combats antibiotic-resistant strains but also works under harsh conditions such as multiple-source contamination, high eutrophic state, and salinity.

Surface-enhanced Raman detection of deoxynivalenol allenol in agricultural products

Fungal toxins are secondary metabolites of fungi. Food is highly susceptible to contamination by various fungal species that produce fungal toxins during production and storage. Fungal toxins can cause either acute or chronic poisoning from long-term, low-dose ingestion. Therefore, fungal toxins have become a topic of international interest as a food safety issue. Deoxynivalenol (DON) is a single-terminal sporam toxin produced predominantly by Fusarium graminae and Fusarium pinkosa. DON is globally one of the most common fungal toxins contaminating grain, food, and feed. Various methods have been applied for screening and detecting DON; however, these methods utilize expensive instruments and entail complex operations, poor repeatability, and low sensitivity. Therefore, the development of a simpler, more rapid, and sensitive sensing technology for DON detection is important for applications within the agriculture and food industry. Recently, surface-enhanced Raman scattering (SERS) has become a rapidly developing spectral analysis technology with unique advantages, including high sensitivity, high throughput, and rapid response rates. Therefore, attempts have been made to apply the SERS technique to detecting DON. However, due to the limitations concerning SERS substrates, the currently established SERS method exhibits serious problems, including low sensitivity and weak anti-interference ability, and cannot meet the requirements of sample detection. Recently, our group has prepared aggregated silver nanoparticles (a-AgNPs/CDs) with high SERS activity by using single-layer carbon-based dots (CDs) as a capping agent. Moreover, the obtained materials (a-AgNPs/CDs) were combined with hydrogel technology to prepare novel hydrogel SERS chips. The obtained SERS chips exhibited several advantages over traditional SERS substrates, such as high sensitivity, long-term stability, improved uniformity, and strong anti-interference capabilities. Herein, a novel SERS method for rapid screening and detection of DON in grains was established using a portable Raman spectrometer based on the developed hydrogel SERS chips. The main experimental conditions were optimized before the SERS detection of DON; this included the optimization of the hydrogel SERS chip soaking temperature and time in the DON solution. It was found that the optimal soaking temperature and time were 40 ℃ and 5 min, respectively. Under the optimal SERS detection conditions, the linear response range of DON was 1-10000 μg/kg (correlation coefficient (R2)=0.9967), and the limit of detection (LOD) was 0.14 μg/kg. Due to the unique pore size structure of the hydrogel, common sugar, protein, oil, pigment, and other interfering substances in the sample matrix were blocked outside the hydrogel. Therefore, only simple extraction was required while detecting complex samples. This method was applied to detecting DON in wheat flour, yielding recoveries of 97.3%-103% with relative standard deviations of 4.2%-5.0%. The established SERS method for DON detection exhibits a broader response range, high sensitivity, good repeatability, rapid response, simple operation, and strong anti-interference capability. This shows that the laboratory-constructed hydrogel SERS chip has excellent potential for rapid screening and detection of biotoxins in food.

Designed Growth of AgNP Arrays for Anti-counterfeiting Based on Surface-Enhanced Raman Spectroscopy Signals.

Based on etched PS sphere arrays, the different growths of Ag nanoparticles with tunable LSPR are designed when SiO2-25 nm/Ag-30 nm/SiO2-100 nm sandwich nanocavity structures are annealed at 500 °C, including the hexagonal silver nanoparticle rings, circular silver nanoparticle rings, and aggregated silver nanoparticles. The uniformity of particle size and regularity of position generate enhanced electromagnetic field and good surface-enhanced Raman spectroscopy signals as confirmed by UV-vis observation and finite difference time domain method simulation. The developed nanostructures are effectively used as stable, nonreproducible, and markable anti-counterfeiting signs.

Bimetallic Assembled Silver Nanoparticles Impregnated in Aspergillus fumigatus Extract Damage the Bacterial Membrane Surface and Release Cellular Contents

The bactericidal effects of nanomaterials play an essential role in cytoplasmic leakage, leading to bacterial cell death. In this study, silver nanoparticles (AgNPs) were synthesized using a fungal extract of Aspergillus fumigatus (A. fumigatus). The physicochemical properties of the bare and myco-synthesized AgNPs (MS-AgNPs) were examined by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, ultraviolet–visible (UV–vis) spectroscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and transmission electron microscopy (TEM). XRD revealed the crystalline structure of the prepared NPs. The FTIR spectrum of the MS-AgNPs revealed the presence of the stretching vibrations of hydroxyl (−OH) and carbonyl groups (C=O). The UV results showed absorption from 450 nm to 590 nm, confirming the synthesis of the AgNPs. SEM and TEM showed rough cubic shapes (spheres), 20–60 nm in size, while EDX confirmed the presence of 60% Ag in the sample. The MS-AgNPs revealed the highest antibacterial activity against Staphylococcus aureus, with a zone of inhibition of 18.21 ± 2.1 mm, followed by Shigella dysenteriae and Salmonella typhi. The bimetallic-AgNPs played a vital role in cell membrane damage and the release of cellular contents, specifically nucleic acids and proteins. These results suggest that MS-AgNPs have promising antimicrobial capabilities and might be beneficial for an extensive array of biological applications.

In Situ SERS Sensing by a Laser-Induced Aggregation of Silver Nanoparticles Templated on a Thermoresponsive Polymer.

A stimuli-responsive (pH- and thermoresponsive) micelle-forming diblock copolymer, poly(1,2-butadiene)290-block-poly(N,N-dimethylaminoethyl methacrylate)240 (PB-b-PDMAEMA), was used as a polymer template for the in situ synthesis of silver nanoparticles (AgNPs) through Ag+ complexation with PDMAEMA blocks, followed by the reduction of the bound Ag+ with sodium borohydride. A successful synthesis of the AgNPs on a PB-b-PDMAEMA micellar template was confirmed by means of UV–Vis spectroscopy and transmission electron microscopy, wherein the shape and size of the AgNPs were determined. A phase transition of the polymer matrix in the AgNPs/PB-b-PDMAEMA metallopolymer hybrids, which results from a collapse and aggregation of PDMAEMA blocks, was manifested by changes in the transmittance of their aqueous solutions as a function of temperature. A SERS reporting probe, 4-mercaptophenylboronic acid (4-MPBA), was used to demonstrate a laser-induced enhancement of the SERS signal observed under constant laser irradiation. The local heating of the AgNPs/PB-b-PDMAEMA sample in the laser spot is thought to be responsible for the triggered SERS effect, which is caused by the approaching of AgNPs and the generation of “hot spots” under a thermo-induced collapse and the aggregation of the PDMAEMA blocks of the polymer matrix. The triggered SERS effect depends on the time of a laser exposure and on the concentration of 4-MPBA. Possible mechanisms of the laser-induced heating for the AgNPs/PB-b-PDMAEMA metallopolymer hybrids are discussed.

Optical Trapping of Plasmonic Nanoparticles for In Situ Surface-Enhanced Raman Spectroscopy Characterizations.

Surface-enhanced Raman spectroscopy (SERS) enables the ultrasensitive detection of analyte molecules in various applications due to the enhanced electric field of metallic nanostructures. Salt-induced silver nanoparticle aggregation is the most popular method for generating SERS-active substrates; however, it is limited by poor reproducibility, stability, and biocompatibility. The present protocol integrates optical manipulation and SERS detection to develop an efficient analytical platform to address this. A 1064 nm trapping laser and a 532 nm Raman probe laser are combined in a microscope to assemble silver nanoparticles, which generate plasmonic hotspots for in situ SERS measurements in aqueous environments. Without aggregating agents, this dynamic plasmonic silver nanoparticle assembly enables an approximately 50-fold enhancement of the analyte molecule signal. Moreover, it provides spatial and temporal control to form the SERS-active assembly in as low as 0.05 nM analyte-coated silver nanoparticle solution, which minimizes the potential perturbation for in vivo analysis. Hence, this optical trapping-integrated SERS platform holds great potential for efficient, reproducible, and stable molecular analyses in liquids, especially in aqueous physiological environments.

Optical Trapping of Plasmonic Nanoparticles for <em>In Situ</em> Surface-Enhanced Raman Spectroscopy Characterizations

Surface-enhanced Raman spectroscopy (SERS) enables the ultrasensitive detection of analyte molecules in various applications due to the enhanced electric field of metallic nanostructures. Salt-induced silver nanoparticle aggregation is the most popular method for generating SERS-active substrates; however, it is limited by poor reproducibility, stability, and biocompatibility. The present protocol integrates optical manipulation and SERS detection to develop an efficient analytical platform to address this. A 1064 nm trapping laser and a 532 nm Raman probe laser are combined in a microscope to assemble silver nanoparticles, which generate plasmonic hotspots for in situ SERS measurements in aqueous environments. Without aggregating agents, this dynamic plasmonic silver nanoparticle assembly enables an approximately 50-fold enhancement of the analyte molecule signal. Moreover, it provides spatial and temporal control to form the SERS-active assembly in as low as 0.05 nM analyte-coated silver nanoparticle solution, which minimizes the potential perturbation for in vivo analysis. Hence, this optical trapping-integrated SERS platform holds great potential for efficient, reproducible, and stable molecular analyses in liquids, especially in aqueous physiological environments.

A skin-inspired biomimetic strategy to fabricate cellulose enhanced antibacterial hydrogels as strain sensors

With the development of wearable devices, the fabrication of strong, tough, antibacterial, and conductive hydrogels for sensor applications is necessary but remains challenging. Here, a skin-inspired biomimetic strategy integrated with in-situ reduction has been proposed. The self-assembly of cellulose to generate a cellulose skeleton was essential to realize the biomimetic structural design. Furthermore, in-situ generation of silver nanoparticles on the skeleton was easily achieved by a heating process. This process not only offered the excellent antibacterial property to hydrogels, but also improved the mechanical properties of hydrogels due to the elimination of negative effect of silver nanoparticles aggregation. The highest tensile strength and toughness could reach 2.0 MPa and 11.95 MJ/m3, respectively. Moreover, a high detection range (up to 1300%) and sensitivity (gauge factor = 4.4) was observed as the strain sensors. This study provides a new horizon to fabricate strong, tough and functional hydrogels for various applications in the future.

Structural color printing via polymer-assisted photochemical deposition

Structural color printings have broad applications due to their advantages of long-term sustainability, eco-friendly manufacturing, and ultra-high resolution. However, most of them require costly and time-consuming fabrication processes from nanolithography to vacuum deposition and etching. Here, we demonstrate a new color printing technology based on polymer-assisted photochemical metal deposition (PPD), a room temperature, ambient, and additive manufacturing process without requiring heating, vacuum deposition or etching. The PPD-printed silver films comprise densely aggregated silver nanoparticles filled with a small amount (estimated <20% volume) of polymers, producing a smooth surface (roughness 2.5 nm) even better than vacuum-deposited silver films (roughness 2.8 nm) at ~4 nm thickness. Further, the printed composite films have a much larger effective refractive index n (~1.90) and a smaller extinction coefficient k (~0.92) than PVD ones in the visible wavelength range (400 to 800 nm), therefore modulating the surface reflection and the phase accumulation. The capability of PPD in printing both ultra-thin (~5 nm) composite films and highly reflective thicker film greatly benefit the design and construction of multilayered Fabry–Perot (FP) cavity structures to exhibit vivid and saturated colors. We demonstrated programmed printing of complex pictures of different color schemes at a high spatial resolution of ~6.5 μm by three-dimensionally modulating the top composite film geometries and dielectric spacer thicknesses (75 to 200 nm). Finally, PPD-based color picture printing is demonstrated on a wide range of substrates, including glass, PDMS, and plastic, proving its broad potential in future applications from security labeling to color displays.

Peptide-Induced Fractal Assembly of Silver Nanoparticles for Visual Detection of Disease Biomarkers.

We report the peptide-programmed fractal assembly of silver nanoparticles (AgNPs) in a diffusion-limited aggregation (DLA) mode, and this change in morphology generates a significant color change. We show that peptides with specific repetitions of defined amino acids (i.e., arginine, histidine, or phenylalanine) can induce assembly and coalescence of the AgNPs (20 nm) into a hyperbranched structure (AgFSs) (∼2 μm). The dynamic process of this assembly was systematically investigated, and the extinction of the nanostructures can be modulated from 400 to 600 nm by varying the peptide sequences and molar ratio. According to this rationale, two strategies of SARS-CoV-2 detection were investigated. The activity of the main protease (Mpro) involved in SARS-CoV-2 was validated with a peptide substrate that can bridge the AgNPs after the proteolytic cleavage. A sub-nanomolar limit of detection (0.5 nM) and the capacity to distinguish by the naked eye in a wide concentration range (1.25-30 nM) were achieved. Next, a multichannel sensor-array based on multiplex peptides that can visually distinguish SARS-CoV-2 proteases from influenza proteases in doped human samples was investigated.