Use Of Gold Nanoparticles Research Articles

Predictive modeling of hypoxic head and neck cancers during fractionated radiotherapy with gold nanoparticle radiosensitization.

Intrinsic radioresistance and increased proliferation rates in head and neck cancers (HNCs) are associated with negative radiotherapy (RT) treatment responses. The use of gold nanoparticles (AuNPs) as radiosensitizers could enable total radiation dose reduction and lowered radiation toxicity. AuNP radiosensitization may overcome hypoxia-induced radioresistance and treatment-induced accelerated repopulation of cancer cells in HNCs, improving radiotherapy outcomes. Tumor control was determined by considering individual cancer cell responses in probabilistic computational simulations using HYP-RT software for clinical radiotherapy doses and fractionation schedules along with three different nanoparticle administration schedules. Antagonistic tumor hypoxia and rapid tumor regrowth due to accelerated repopulation of cancers cells were taken into consideration. Simulations indicate that tumors that are conventionally uncontrollable can be controlled with AuNP radiosensitization. In simulations where the absence of AuNPs required radiotherapy doses above standard clinical prescriptions, reoccurring AuNP administration allowed for radiation dose reductions below standard clinical dose prescriptions. For example, considering a 2Gy per fraction radiotherapy schedule, tumor control was achieved with 57.2±5.1Gy (P=<0.0001) for weekly AuNP administration and 53.0±4.0Gy (P=<0.0001) for biweekly AuNP administration compared to 69.9±5.8Gy with no radiosensitization. AuNPs decreased the predicted RT total doses required to achieve tumor control via total stem cell elimination, offering an optimistic prediction and method for which hypoxia-induced and rapidly growing radioresistant tumors are treated more effectively. Outcomes are also shown to be sensitive to the RT schedule with data for hyperfractionated RT indicating the greatest benefits from radiosensitization.

Does repeated gold-nanoparticles administration affect pars distalis hormonal and folliculo-stellate cells in adult male albino rats?

Worldwide, nanoparticles especially gold-nanoparticles (Au-NPs) are widely used in medicine, cancer treatment and cosmetic industry. They are easily conjugated with different biomedical and biological agents and effortlessly absorbed with few side effects. The pars distalis of the pituitary gland is considered as the maestro of the endocrine peripheral glands since it secrets trophic hormones that controls their functions. 5-10% of the non-granular pars distalis cells are folliculo-stellate cells (FSCs) that support the granular cells' functions. The aim of the study was to explore the histological and the biochemical effects of repeated exposure to Au-NPs on the pars distalis in adult male albino rats with highlighting the impact on FSCs. Thirty-six adult male albino rats were divided equally into control group and Au-NPs group (received 40 μg/kg/day of 11 ± 2 nm spherical Au-NPs orally for 2 weeks). Then, rats were euthanized and deposition of Au-NPs in pars distalis was investigated. Biochemical investigations and histological studies including hematoxylin and eosin staining, periodic acid Schiff's reaction, immunohistochemistry (IHC) for S-100, connexin 43 (Cx43) and Cytochrome-C (Cyt-C) as well as electron-microscopic and morphometric studies were carried out. The Au-NPs group demonstrated structural disorganization in the pars distalis, inflammation, congestion and increased extracellular PAS-positive colloid deposition due to the accumulation of Au-NPs. A significant increase in the immunoreactivity of S-100, Cx43 and Cyt-c, along with a significant increase in TNF-a, MDA, and bFGF content in the pituitary homogenates, was noted as compared to the control group. Ultrastructurally, degenerative changes were observed in the secretory cells. FSCs showed proliferation and increased phagocytic activity. Repetitive exposure of adult male albino rats to Au-NPs prompted the accumulation of these nanoparticles in the pars distalis that was accompanied by cellular degeneration and dysfunction of the secretory cell and proliferation of FSCs. Thus, monitoring of the pars distalis hormonal levels might be useful for early detection of some hazardous effects possibly associated with the use of gold-nanoparticles.

Antibacterial and antibiofilm activities of marine polysaccharide laminarin formulated gold nanoparticles: An ecotoxicity and cytotoxicity assessment

In recent years the use of gold nanoparticles (AuNPs) has risen in fields as different as biomedicine or electronics. The most widely used method for their synthesis is citrate reduction, but alternative green methods are being sought. In this sense, the substitution of citrate with natural compounds such as marine polysaccharides is a noteworthy option. In the present study, laminarin formulated AuNPs (Lm-AuNPs) were synthesized, and their antibacterial and antibiofilm activities, toxicity, and ecotoxicity were evaluated. First, the physicochemical features of the green synthesized Lm-AuNPs were thoroughly evaluated. Lm-AuNPs were highly crystalline, had a spherical shape and a mean particle size of 10–80 nm. The photocatalytic activity of Lm-AuNPs was assessed by the degradation of Methylene Blue (MB), revealing a high decomposition from 60 min. The in vitro antibacterial activity of Lm-AuNPs against the aquatic fish pathogen Aeromonas hydrophila was confirmed by the inhibition of bacterial growth. Furthermore, the antibiofilm activity against A. hydrophila was evaluated, detecting the biofilm growth inhibition at 100 μg/ml of Lm-AuNPs. The in vivo antibacterial activity evaluation was carried out by treating Artemia salina infected by A. hydrophila with Lm-AuNPs, which decreased the mortality rate. Moreover, the cytotoxicity evaluation indicated that Lm-AuNPs did not affect Vero cells' viability up to 100 μg/ml. Likewise, the ecotoxicity assessment of Lm-AuNPs on fresh and marine water microcrustaceans Daphnia similis and Artemia salina showed no significant mortality up to 400 μg/ml.

Effect of gold nanoparticle treated dorsal root ganglion cells on peripheral neurite differentiation

The use of gold nanoparticles (AuNps) in applications connected to the peripheral nervous system (PNS) holds much promise in terms of therapeutic and diagnostic strategies. Despite their extensive use, a clear understanding of their effects on neurons and glia in the PNS is lacking. In this study, we set out to examine the effects of AuNps on dorsal root ganglion (DRG) cells, and how such AuNp-exposed cells could in-turn affect neurite differentiation.DRG cultures were exposed to mono-dispersed spherical-shaped AuNps of diameter 24.3 ± 2.3, 109.2 ± 14.7 or 175 ± 19.2 nm at varying concentrations. Cellular uptake and viability were quantified using flow-cytometry. Neurite differentiation was quantified using neurite tracing analysis in PC-12 and DRG neurons exposed to conditioned media derived from AuNp-treated DRG cells.Both neurons and glia were found to internalize AuNps. DRG cell viability was significantly reduced upon treatment with higher concentration of 175 nm sized AuNps, while 24 nm and 109 nm sized AuNps had no effect. Further, conditioned media from AuNp-treated DRG cells produced comparable neurite outgrowth and neurite branching measurement as controls in PC-12 and DRG neurons.DRG cells were quite resilient to AuNp exposure in mild-moderate concentration. AuNp-exposed DRG cells, irrespective of size and concentration range tested, did not affect neuronal differentiation.

The Role of Polymeric Coatings for a Safe-by-Design Development of Biomedical Gold Nanoparticles Assessed in Zebrafish Embryo.

In the biomedical field, gold nanoparticles (GNPs) have attracted the attention of the scientific community thanks to their high potential in both diagnostic and therapeutic applications. The extensive use of GNPs led researchers to investigate their toxicity, identifying stability, size, shape, and surface charge as key properties determining their impact on biological systems, with possible strategies defined to reduce it according to a Safe-by-Design (SbD) approach. The purpose of the present work was to analyze the toxicity of GNPs of various sizes and with different coating polymers on the developing vertebrate model, zebrafish. In particular, increasing concentrations (from 0.001 to 1 nM) of 6 or 15 nm poly-(isobutylene-alt-maleic anhydride)-graft-dodecyl polymer (PMA)- or polyethylene glycol (PEG)-coated GNPs were tested on zebrafish embryos using the fish embryo test (FET). While GNP@PMA did not exert significant toxicity on zebrafish embryos, GNP@PEG induced a significant inhibition of embryo viability, a delay of hatching (with the smaller size NPs), and a higher incidence of malformations, in terms of tail morphology and eye development. Transmission electron microscope analysis evidenced that the more negatively charged GNP@PMA was sequestered by the positive charges of chorion proteins, with a consequent reduction in the amount of NPs able to reach the developing embryo and exert toxicological activity. The mild toxic response observed on embryos directly exposed to GNP@PMA suggest that these NPs are promising in terms of SbD development of gold-based biomedical nanodevices. On the other hand, the almost neutral GNP@PEG, which did not interact with the chorion surface and was free to cross chorion pores, significantly impacted the developing zebrafish. The present study raises concerns about the safety of PEGylated gold nanoparticles and contributes to the debated issue of the free use of this nanotool in medicine and nano-biotechnologies.

The Combined Use of Gold Nanoparticles and Infrared Radiation Enables Cytosolic Protein Delivery.

Cytosolic protein delivery remains elusive. The inability of most proteins to cross the cellular membrane is a huge hurdle. Here we explore the unique photothermal properties of gold nanorods (AuNRs) to trigger cytosolic delivery of proteins. Both partners, protein and AuNRs, are modified with a protease-resistant cell-penetrating peptide with nuclear targeting properties to induce internalization. Once internalized, spatiotemporal control of protein release is achieved by near-infrared laser irradiation in the safe second biological window. Importantly, catalytic amounts of AuNRs are sufficient to trigger cytosolic protein delivery. To the best of our knowledge, this is the first time that AuNRs with their maximum of absorption in the second biological window are used to deliver proteins into the intracellular space. This strategy represents a powerful tool for the cytosolic delivery of virtually any class of protein.

Neuroinflammatory Regulation of Gold Nanoparticles Conjugated to Ethylene Dicysteine Diethyl Ester in Experimental Autoimmune Encephalomyelitis

Multiple sclerosis (MS) is a demyelinating chronic autoimmune inflammatory disease of the central nervous system (CNS). A large amount of proinflammatory cytokines is released in the CNS from the self-reactive T cells infiltrate, leading to the destruction of the myelin sheath and contributing to the development of MS. Several drugs have emerged in recent years to treat MS, and studies have shown that gold nanoparticles (GNPs) have anti-inflammatory properties in autoimmune diseases. Thus, the effects of GNP conjugation to ethylene dicysteine diethyl ester (ECD) were evaluated in C57BL/6 female mice exposed to experimental MS. Animals were exposed to experimental autoimmune encephalitis (EAE) induced by myelin oligodendrocyte glycoprotein (MOG35-55) in complete Freund's adjuvant supplemented with Mycobacterium tuberculosis. The clinical and cerebral effects of the different doses of ECD-GNPs (0.3, 0.6, and 1.0 mg/kg) were first studied, and the results showed that the group treated with 0.6 mg/kg ECD-GNPs improved clinical symptoms, inflammatory infiltrate, and myelin integrity. In the following step, GNPs and ECD-GNPs (0.6 mg/kg) showed improvements in the clinical signs of the disease. Moreover, there was a reduction in the levels of proinflammatory cytokines in both groups compared to EAE, and only the isolated use of GNPs increased IL-4 expression. Both NF-κB and TGFβ immunoexpression were significantly reduced following EAE + GNPs and EAE + ECD-GNPs treatment. In conclusion, GNPs and ECD-GNPs at 0.6 mg/kg attenuate the neurological signs of EAE likely due to inhibition of neuroinflammation induced by EAE.

Gold nanoparticles to enhance ophthalmic imaging.

The use of gold nanoparticles as diagnostic tools is burgeoning, especially in the cancer community with a focus on theranostic applications to both cancer diagnosis and treatment. Gold nanoparticles have also demonstrated great potential for use in diagnostic and therapeutic approaches in ophthalmology. Although many ophthalmic imaging modalities are available, there is still a considerable unmet need, in particular for ophthalmic molecular imaging for the early detection of eye disease before morphological changes are more grossly visible. An understanding of how gold nanoparticles are leveraged in other fields could inform new ways they could be utilized in ophthalmology. In this paper, we review current ophthalmic imaging techniques and then identify optical coherence tomography (OCT) and photoacoustic imaging (PAI) as the most promising technologies amenable to the use of gold nanoparticles for molecular imaging. Within this context, the development of gold nanoparticles as OCT and PAI contrast agents are reviewed, with the most recent developments described in detail.

Advance in the use of gold nanoparticles in the treatment of neurodegenerative diseases: new perspectives.

Advance in the use of gold nanoparticles in the treatment of neurodegenerative diseases: new perspectives.

Gold nanoparticle assisted synthesis of MoS2 monolayers by chemical vapor deposition.

The use of metal nanoparticles is an established paradigm for the synthesis of semiconducting one-dimensional nanostructures. In this work we study their effect on the synthesis of two-dimensional semiconducting materials, by using gold nanoparticles for chemical vapor deposition growth of two-dimensional molybdenum disulfide (MoS2). In comparison with the standard method, the employment of gold nanoparticles allows us to obtain large monolayer MoS2 flakes, up to 20 μm in lateral size, even if they are affected by the localized overgrowth of MoS2 bilayer and trilayer islands. Important modifications of the optical and electronic properties of MoS2 triangular domains are reported, where the photoluminescence intensity of the A exciton is strongly quenched and a shift to a positive threshold voltage in back-gated field effect transistors is observed. These results indicate that the use of gold nanoparticles influences the flake growth and properties, indicating a method for possible localized synthesis of two-dimensional materials, improving the lateral size of monolayers and modifying their properties.

Disclosing the Interaction of Gold Nanoparticles with Aβ(1-40) Monomers through Replica Exchange Molecular Dynamics Simulations.

Amyloid-β aggregation is one of the principal causes of amyloidogenic diseases that lead to the loss of neuronal cells and to cognitive impairments. The use of gold nanoparticles treating amyloidogenic diseases is a promising approach, because the chemistry of the gold surface can be tuned in order to have a specific binding, obtaining effective tools to control the aggregation. In this paper, we show, by means of Replica Exchange Solute Tempering Molecular Simulations, how electrostatic interactions drive the absorption of Amyloid-β monomers onto citrates-capped gold nanoparticles. Importantly, upon binding, amyloid monomers show a reduced propensity in forming β-sheets secondary structures that are characteristics of mature amyloid fibrils.

Radiolabeled Gold Nanoparticles for Imaging and Therapy of Cancer.

In the Last decades, nanotechnology has provided novel and alternative methodologies and tools in the field of medical oncology, in order to tackle the issues regarding the control and treatment of cancer in modern society. In particular, the use of gold nanoparticles (AuNPs) in radiopharmaceutical development has provided various nanometric platforms for the delivery of medically relevant radioisotopes for SPECT/PET diagnosis and/or radionuclide therapy. In this review, we intend to provide insight on the methodologies used to obtain and characterize radiolabeled AuNPs while reporting relevant examples of AuNPs developed during the last decade for applications in nuclear imaging and/or radionuclide therapy, and highlighting the most significant preclinical studies and results.

Gold nanoparticle-based colorimetric and electrochemical sensors for the detection of illegal food additives.

Lately, scandals associated with the illegal addition of poisonous chemicals to food for commercial interests have been gradually disclosed to the public. Problems related to food safety do not only harm public health but also affect the stability of economic and social development. Food safety has become a common issue in society, and strengthening the related regulations have become increasingly important. Although conventional techniques are accurate and sensitive in the detection of the vast majority of illegal food additives, they rely on time-consuming, labor-intensive procedures that depend on expensive instruments. Thus, efficient and rapid identification of poisonous, illegal additives in food is a crucial task in analytical chemistry. Recently, in this context, gold nanoparticles (GNPs) have attracted considerable attention because of their optical, electronic, catalytic, and chemical properties. Their excellent properties have facilitated the widespread use of GNPs in different sensors. This review covers the two most common GNP-based sensors with colorimetric and electrochemical responses, which have proven to be effective in the detection of illegal additives. The GNP-based sensors comply with the requirement of modern analysis, such as high selectivity, sensitivity, simplicity, rapidity, and portability. Thus, they have great potential as powerful sensing tools for food safety screening. This review elucidates the utility and advances of GNP-based colorimetric and electrochemical sensors for the detection of illegal additives in the food industry and in the supervision of food quality and safety. Additionally, an outlook of the trends and future development of research on these sensors is provided.

Enhanced effect of Amikacin in conjugation with gold nanopartcles as a carrier to kill Pseudomonas aeruginosa

Pseudomonas aeruginosa is a significant cause of nosocomial infections. Infection caused by this organism is difficult to treat due to the presence of its innate resistance to many antibiotics. Conjugation of antimicrobial drugs with nanoparticles has emerged as an innovative and promising alternative that enhances therapeutic effectiveness. The current study focuses on the use of gold nanoparticles (GNPs) as a carrier to enhance the antibacterial effect of amikacin against P. aeruginosa. Amikacin was conjugated with GNPs. The success of conjugation was studied by UV/Vis and FTIR spectroscopies. The labeling efficiency was measured by HPLC and atomic absorption spectrometer analyses. The antibacterial activity of amikacin-GNPs conjugate was investigated by disc diffusion and liquid broth dilution methods. The labeling efficiency showed that 450 amikacin molecules were attached to each GNP. The zone of growth inhibition of amikacin-GNPs complex and amikacin by disc diffusion method were 37± 0.118 and 35± 0.149 mm. Minimum inhibitory concentration (MIC) of the conjugate and amikacin alone were determined 23.43 and 46.87, mg/ml, respectively. Minimum bactericidal concentration (MBC) of the conjugate and amikacin alone were determined 46.87 and 93.75 mg/ml, respectively. The results showed the enhanced antibacterial effect of amikacin-GNPs complex in comparison with amikacin alone against P. aeruginosa.

In silico modeling of cellular probabilistic nanoparticle radiosensitization in head and neck cancers.

Background: The use of gold nanoparticles (AuNPs) as radiosensitizers may offer a new approach in the treatment of head and neck cancers; minimizing treatment-associated toxicities and improving patient outcomes. AuNPs promote localized dose deposition; permitting improved local control and/or dose reduction. Aim: This work aimed to address the theoretical optimization of radiation doses, fractionation and nanoparticle injection schedules to maximize therapeutic benefits. Materials & methods: Probabilistic nanoparticle sensitization factors were incorporated into the individual cell-based HYP-RT computer model of tumor growth and radiotherapy. Results: Total dose outcomes across all radiation therapy treatment regimens were found to be significantly reduced with the presence of AuNPs, with bi-weekly injections showing the most decrease. Conclusion: Outcomes suggest the need for regular AuNP administration to permit effective radiosensitization.

Immune Response of Mice Against Babesia canis Antigens is Enhanced When Antigen is Coupled to Gold Nanoparticles.

The aim of this study was to isolate Babesia canis soluble antigens and to investigate the effect of their conjugates with gold nanoparticles on the immunogenicity in laboratory animals. A procedure was developed for isolating and purifying B. canis antigens. The isolated culture antigen of B. canis 495 was coupled to gold nanoparticles, and the conjugate was used to immunize laboratory mice. Western blotting showed that the resultant antiserum specifically recognized the proteins of the B. canis strains isolated from naturally infected dogs. The antibody titer, the respiratory activity of peritoneal macrophages, the proliferative activity of splenocytes, and the production of cytokines were maximal when the animals were immunized with the antigen-nanoparticle conjugate emulsified in complete Freund's adjuvant. Without adjuvant, the babesial antigen was weakly immunogenic. Therefore, the use of gold nanoparticles as an antigen carrier induced a broad immune response involving both cellular and humoral responses. The antibodies raised by the proposed procedure are potentially effective at immunodetection of Babesia canis infections in dogs.

Optical Density Optimization of Malaria Pan Rapid Diagnostic Test Strips for Improved Test Zone Band Intensity.

For the last few decades, the immunochromatographic assay has been used for the rapid detection of biological markers in infectious diseases in humans and animals The assay, also known as lateral flow assay, is utilized for the detection of antigen or antibody in human infectious diseases. There are a series of steps involved in the development of these immuno-chromatographic test kits, from gold nano colloids preparation to nitrocellulose membrane coating (NCM). These tests are mostly used for qualitative assays by a visual interpretation of results. For the interpretation of the results, the color intensity of the test zone is therefore very significant. Herein, the study was performed on a malaria antigen test kit. Several studies have reported the use of gold nanoparticles (AuNPs) with varying diameters and its binding with various concentrations of protein in order to optimize tests. However, none of these studies have reported how to fix (improve) test zone band intensity (color), if different sized AuNPs were synthesized during a reaction and when conjugated equally with same amount of protein. Herein, different AuNPs with average diameter ranging from 10 nm to 50 nm were prepared and conjugated equally with protein concentration of 150 µg/mL with KD = 1.0 × 10−3. Afterwards, the developed kits’ test zone band intensity for all different sizes AuNPs was fixed to the same band level (high) by utilization of an ultraviolet-visible spectrophotometer. The study found that the same optical density (OD) has the same test zone band intensity irrespective of AuNP size. This study also illustrates the use of absorption maxima (λ max) techniques to characterize AuNPs and to prevent wastage of protein while developing immunochromatographic test kits.

Volumetric bubble display with a gold-nanoparticle-containing glycerin screen.

A key issue in the development of volumetric bubble displays whose voxels are femtosecond laser-excited bubbles is to enlarge the size of displayed graphics. In our previous research in which used glycerin as a screen, this size was less than several millimeters. To increase the size, it is important to reduce the excitation energy, because increasing the display size leads results in a larger focus volume due to the use of laser scanning optics with a low numerical aperture and requires more laser energy to excite the material. The use of gold nanoparticles in glycerin has been proposed as one way of reducing the excitation energy, because such materials are commercially available with controlled shapes, and consequently a controlled absorption spectrum. It was found that glycerin containing gold nanoparticles (GNPs), including gold nanospheres (GNSs) and gold nanorods (GNRs), reduced the pulse energy required for bubble generation compared with the use of pure glycerin. Larger GNSs resulted in a smaller threshold energy and, in particular, GNRs resulted in a threshold energy one-quarter that of pure glycerin. It was also found that the density had almost no effect on the threshold energy, but did affect the bubble generation probability. Finally, it was demonstrated that the bubble graphics with a size on the order of centimeters were rendered in GNR-containing glycerin.

Synthesis and Analytical Characterization of Gold Nanoparticles using Microwave-Assisted Extraction System and Study their Application in Degradation

Preparation of gold nanoparticles (AuNPs) was done by the addition of tetrachloroaurate (HAuCl4) to dodonaea viscose (L.) leaves watery extract. The procedure was performed in microwave-assisted extraction (MAE). Dodonaea viscose (L.) watery extract functions as a reducing and capping agent to synthesis AuNPs. The gold nanoparticles was identified by the changes in colour from yellow to red –purple, UV-vis spectroscopy, and surface plasmon band at (600 nm). (EDX -FESEM) and TEM instruments were used to investigate the element analysis, distribution of nanoparticles and to calculate their sizes and shapes. Energy dispersive X-ray spectra (EDX) was applied for characterization of gold nanoparticles, the detected percentage of gold nanoparticles was (0.52 wt/wt %). The result from TEM shows the nanoparticles with diameter (6-80 nm) and vary shapes. Furthermore, characterization of nanoparticles was performed before and after the formation of gold nanoparticles using FT-IR. The band appeared at 669 cm-1 indicated the gold nanoparticle formation. The synthesized gold nanoparticles have been used for degradation of 6.6 % methylene blue organic dye pollutant in aqueous solution, and also for degradation of aliphatic hydrocarbons in crude oil. The results of degradation were monitored by GC-MS. The breakage of some organic materials and the appearance of new organic materials with less molecular weight and less abundance were achieved. Through the use of gold nanoparticles, it has been observed that a large number of aliphatic compounds have disappeared, especially those with molecular weights 200-288, the loss in the molecular weight is about 40%.

3D‐Printed Biocompatible Scaffolds with Built‐In Nanoplasmonic Sensors

Abstract3D printing strategies have acquired great relevance toward the design of 3D scaffolds with precise macroporous structures, for supported mammalian cell growth. Despite advances in 3D model designs, there is still a shortage of detection tools to precisely monitor in situ cell behavior in 3D, thereby allowing a better understanding of the progression of diseases or to test the efficacy of drugs in a more realistic microenvironment. Even if the number of available inks has exponentially increased, they do not necessarily offer the required functionalities to be used as internal sensors. Herein the potential of surface‐enhanced Raman scattering (SERS) spectroscopy for the detection of biorelevant analytes within a plasmonic hydrogel‐based, 3D‐printed scaffold is demonstrated. Such SERS‐active scaffolds allow for the 3D detection of model molecules, such as 4‐mercaptobenzoic acid. Flexibility in the choice of plasmonic nanoparticles is demonstrated through the use of gold nanoparticles with different morphologies, gold nanorods showing the best balance between SERS enhancement and scaffold transparency. Detection of the biomarker adenosine is also demonstrated as a proof‐of‐concept toward the use of these plasmonic scaffolds for SERS sensing of cell‐secreted molecules over extended periods of time.