Silver nanoparticle-initiated chemiluminescence reaction of luminol-AgNO3 and its analytical application

Versatile Bovine Serum Albumin as Ingenious Electron Operator-Enhanced Photoelectrochemical Biosensing for Ultrasensitive Detection of miRNA

Bovine serum albumin (BSA) has been widely used in biosensors as a blocking agent. Herein, conformist BSA was first exploited as an ingenious operator to enhance the photocurrent response of (2Z,2'Z)-2,2'-(1,4-phenylene)bis(3-(4-(bis(4-methoxyphenyl)amino)phenyl)acrylonitrile) (TPDCN)-based photoelectrochemical (PEC) platform via manipulating the electron transfer process of the detection system. Concretely, the presence of target molecules triggered catalytic hairpin assembly reaction and subsequently powered terminal deoxynucleotidyl transferase-mediated signal amplification to produce the AgNP@BSA-DNA dendrimer nanostructure. After being treated with HNO3, a large amount of BSA could be released from the dendrimer nanostructure. When they were transferred to the TPDCN-based PEC platform, the photocurrent response of the biosensor was largely enhanced because BSA can manipulate the electrons of TPDCN via a well-matched energy level to form a new electron transfer track. Meanwhile, tryptophan (Trp) in BSA could be oxidized to quinone Trp-O under photoirradiation, which can facilitate the oxidation of ascorbate and generate more H+ to promote the migration of photogenerated electrons. As a result, the proposed PEC biosensor exhibits excellent analytical performance for detection of miRNA-21 (as a model target) over a wide linear range of 0.01 to 10,000 pM with detection limit as low as 4.7 fM. Overall, this strategy provides a new perspective on constructing efficient PEC biosensors, which expands the potential applications in bioanalysis and clinical diagnosis.

Utilizing dual carriers assisted by enzyme digestion chemiluminescence signal enhancement strategy simultaneously detect tumor markers CEA and AFP

To measure two tumor biomarkers, alpha-fetoprotein (AFP) and carcinoembryonic antigen (CEA), a dual-carrier CL sensor with restriction enzyme digestion (Exo I) and aptamer technology utilizing gold nanoparticles (hydroxylamine amplification) and horseradish peroxidase (HRP) as the CL signal enhancement in the sensing strategy was formed. These nanoparticles and nano-enzyme were precisely detected and tagged to the appropriate position attributable to the particular recognition of biotin and streptavidin. In this sensing strategy, target markers were further enriched and recognized sensitively by CL following enrichment, and matching strong chemical signals were collected under luminol catalysis, allowing for marker identification. For CEA (0.1-80 ng/mL) and AFP (2-500 ng/mL), the proposed method has a large linear range, with detection limits of 36.6 pg/mL and 0.94 ng/mL, respectively.

Rapid assessment of silver nanoparticle migration from food containers into food simulants using a qualitative method

Migration of silver nanoparticles (AgNPs) from food containers (FCs) has been assessed for the first time using a screening method previously validated. Migration was evaluated using water and 3% acetic acid as food simulants (FSs), from 20 to 70 °C at contact times of 2 h and 10 days. Total and migrated Ag were determined by inductively coupled plasma-mass spectrometry (ICP-MS) in the FCs and FSs, respectively. Then, the screening method was validated, and probability of detection (POD) curves were constructed in both FSs to characterize the response to AgNPs. The results provided by the present screening method showed no release of AgNPs. The FSs in contact with FCs were spiked at levels above, inside and below the unreliability region, with a reliability rate (RLR) of 0.90. Asymmetric flow field flow fractionation coupled to inductively coupled plasma mass-spectrometry (AF4-ICP-MS) was used for confirmative analyses.

Screening-confirmation strategy for nanomaterials involving spectroscopic analytical techniques and its application to the control of silver nanoparticles in pastry samples

The full characterization of nanomaterials (NMs), which requires a range of different and expensive equipment, is not always necessary to meet certain demands of information. Qualitative analytical methods are ideal alternatives when only a piece of information is required. In this work, a qualitative method for the screening of NMs has been developed and statistically validated for the first time, with silver nanoparticles (AgNPs) as a proof of concept. It is based on the generation of chemiluminescence of the luminol/Ag⁺ system in alkaline media in the presence of AgNPs. Measurements are obtained in a short time with a simple instrument. Probability of detection (POD) curves were constructed at three cut-off values next to the limit of detection of the chemiluminescent method. The unreliability region (UR) was from 0.50 to 1.82 μg L^-1. Currently, no regulation on AgNPs exists, but the present method was successfully tested for a hypothetical threshold of 2.5 μg L^-1 of 40 nm AgNPs. The method was applied to silver colored pearls, with silver (E-174) or aluminum (E-173) coating, used for decoration of pastry. Performance parameters such as false negative and positive rates as well as specificity, sensitivity and reliability rates were calculated for validation. The results of the screening method were confirmed by asymmetric flow field flow fractionation coupled to inductively coupled plasma mass spectrometry (AF4-ICP-MS). The proposed screening method is simple, fast, economic, and easy to transfer to routine laboratories in the field of food safety.

Engineering WS2–Au–HRP-assisted multiple signal amplification strategy for chemiluminescence immunoassay of prostate specific antigen

Engineering of a WS₂–Au–HRP-assisted multiple signal amplification strategy for CL immunoassay of PSA.

Nanomaterial-enhanced chemiluminescence reactions and their applications

Chemiluminescence (CL) analysis is a trace analytical method that possesses advantages including high sensitivity, wide linear range, easy operation, and simple instruments. With the development of nanotechnology, many nanomaterial (NM)-enhanced CL systems have been established in recent years and applied for the CL detection of metal ions, anions, small molecules, tumor markers, sequence-specific DNA, and RNA. This review summarizes the research progress of the nanomaterial-enhanced CL systems the past five years. These CL reactions include luminol, peroxyoxalate, lucigenin, ultraweak CL reactions, and so on. The CL mechanisms of the nanomaterial-enhanced CL systems are discussed in the first section. Nanomaterials take part in the CL reactions as the catalyst, CL emitter, energy acceptor, and reductant. Their applications are summarized in the second section. Finally, the challenges and opportunities are discussed.

Synergistic ROS-Associated Antimicrobial Activity of Silver Nanoparticles and Gentamicin Against Staphylococcus epidermidis

Introduction

Increasing bacteria resistance to antibiotics is a major problem of healthcare system. There is a need for solutions that broaden the spectrum of bactericidal agents improving the efficacy of commonly used antibiotics. One of the promising directions of search are silver nanoparticles (obtained by different methods and displaying diversified physical and chemical properties), and their combination with antibiotics.

Purpose

In this study, we tested the role of reactive oxygen species in the mechanism of synergistic antibacterial activity of gentamicin and Tween-stabilized silver nanoparticles against gentamicin-resistant clinical strains of Staphylococcus epidermidis.

Methods

Synergistic bactericidal activity of gentamicin and silver nanoparticles stabilized with non-ionic detergent (Tween 80) was tested by the checkerboard titration method on microtiter plates. Detection of reactive oxygen species was based on the chemiluminescence of luminol.

Results

Hydrophilic non-ionic surface functionalization of silver nanoparticles enabled the existence of non-aggregated active nanoparticles in a complex bacterial culture medium. Tween-stabilized silver nanoparticles in combination with gentamicin exhibited bactericidal activity against multidrug-resistant biofilm forming clinical strains of Staphylococcus epidermidis. A synergistic effect significantly decreased the minimal inhibitory concentration of gentamicin (the antibiotic with numerous undesirable effects). Gentamicin significantly enhanced the generation of reactive oxygen species by silver nanoparticles.

Conclusion

Generation of reactive oxygen species by Tween-coated metallic silver nanoparticles was significantly enhanced by gentamicin, confirming the hypothesis of oxidative-associated mechanism of the synergistic antibacterial effect of the gentamicin-silver nanoparticles complex.

Surface Metallization of Porous Polymer Materials for Multifunctional Applications

Porous materials have attracted great interest in recent years, and a variety of surface modification methods have been developed to endow porous materials with multifunctional applications. Herein, multifunctional porous materials are fabricated based on surface metallization. Metallized sponges with Ag and Cu are highly hydrophobic and are still hydrophobic under oil. The metallized sponges selectively adsorb oils from oil/water mixtures and can completely remove oils from water. We further demonstrate continuous oil-water separation by the metallized sponges with the aid of a peristaltic pump. The Ag-metallized materials show high catalytic performance for both chemical reduction and dye degradation. The catalytic reduction efficiency of 4-nitrophenol reaches 97.7% within 60 min and remains as high as 96% after 15 cycles. Moreover, the metallized materials show 99.99% bactericidal efficiency for both Staphylococcus aureus and Escherichia coli. Particularly, the Cu-metallized materials exhibit stable conductivity under deformation; and metal patterns are realized via the metallization method combined with a patterned mask, which may provide a feasible approach for flexible electronics. This work provides a versatile method to introduce metal coatings to porous materials, broadening the applications of porous materials.

Synthesis of gold nanoparticles using Crinum macowanii bulb extracts and the application of these materials in blood detections at crime scenes

We here in report the synthesis of gold nanoparticles (AuNPs) using a Crinum macowanii bulb water extract. The as-synthesized AuNPs were characterized using ultraviolet-visible spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction, transmission electron microscopy, and a zeta potential-sizer. The results showed that the as-synthesized AuNPs were crystalline and mostly spherical in shape with a small mixture of triangular, tetrahedral, hexagonal, octagonal, and diamond shapes. The as-synthesized AuNPs together with those synthesized by conventional methods were subsequently used as enhancers for the luminol signal in blood detection. It was noted that the AuNPs synthesized from the Crinum macowanii bulb water extract could enhance the chemiluminescence signal for blood detection by luminol to the same extent as AuNPs prepared by conventional methods. Furthermore, both types of AuNPs served as fluorescence enhancers for blood detection when luminol was replaced with the bulb water extract.

In Situ Generation of Prussian Blue with Potassium Ferrocyanide to Improve the Sensitivity of Chemiluminescence Immunoassay Using Magnetic Nanoparticles as Label

Using magnetic nanoparticles (MNPs) as a label in immunoassay (IA) possesses advantages such as high specific surface area, simple modification process. However, the catalytic activity of MNPs is low, which limits their applications in IA. The present study found it interesting that potassium ferrocyanide reacts with MNPs, leading to the in situ generation of Prussian blue. The produced Prussian blue shows high catalytic activity on a luminol chemiluminescent (CL) reaction. Therefore, a simple and sensitive immunoassay for rabbit IgG (rIgG) as model analyte using MNPs as label was developed. The CL intensity had a linear increase with the concentration of rIgG that ranged from 0.625 to 20 ng mL^-1. The limit of detection was calculated to be 0.59 ng mL^-1. In addition, the applicability of this method was evaluated using the standard addition method. The recovery ranged from 80.0% to 115.0%. What's more, the proposed CLIA method based on in situ generation of Prussian blue with MNPs was also applied to the detection of carcinoembryonic antigen (CEA) and hepatitis B virus (HBV)-related sequence-specific DNA. The LOD for the detection of CEA and sequence-specific DNA was estimated to be 0.28 ng mL^-1 and 0.044 pmol, respectively.

Quenching of Luminol Fluorescence at Nano-Bio Interface: Towards the Development of an Efficient Energy Transfer System

Surface modified colloidal gold (Au) and silver (Ag) nanoparticles (NPs) were used as efficient quenchers of luminol (LH₂) fluorescence either in homogeneous aqueous medium or its noncovalent assembly with bovine serum albumin (BSA). The mechanism as well as the extent of fluorescence quenching was found to be strongly dependent on the nature of the nanoparticles. While simple static type fluorescence quenching mechanism was perceived with AuNP, a more complex protocol involving quenching sphere model was envisaged for AgNP quenching. Nevertheless, the magnitude of Stern-Volmer (SV) quenching constant (K_SV ~ 10⁸-10¹⁰ M^-1) was calculated to be ca. 10⁴ times more for surface quoted NPs in comparison with BSA-NP bioconjugates system. On the other hand, a highly efficient (E ≈ 95%) energy transfer (ET) process was predicted for LH₂ captured in the hydrophobic assembly with BSA in presence of AgNP as an acceptor. The ET efficiency is critically dependent on the concentration of BSA and nicely correlated with the extent of NP surface coverage. However, fluorescence quenching on AuNP surface is relatively less responsive towards protein concentration, primarily due to the difference in surface activity as well as the mode of interaction of the protein with NPs. Graphical Abstract Energy transfer from excited luminol to metal nanoparticles is strongly modulated in presence of serum albumins.

Silver nanoparticles for the visual detection of lomefloxacin in the presence of cystine

A novel optical sensors for lomefloxacin based on the plasma resonance properties of silver nanoparticles (AgNPs) for the first time. The hydrogen bonds and electrostatic force between the lomefloxacin and AgNPs could induce the change in color and absorption spectra of AgNPs suspension, which provided a theoretical basis for the optical detection of lomefloxacin. In addition, we made the AgNPs-lomefloxacin detection system reach the critical point of discoloration by adding cystine to improve the sensitivity. Furthermore, the influence of some factors such as temperature, reaction time and pH on the AgNPs-lomefloxacin detection system was investigated. The results of UV-vis spectra showed that the absorption ratio (A₅₂₀/A₃₉₅) was linear with the concentration of lomefloxacin in the range from 0.2 to 5 μmol/L with linear coefficients of 0.991. The proposed method can be applied to detecting lomefloxacin with an ultralow detection limit of 0.6 μmol/L without any complicated instruments and complex pretreatment. The selectivity of AgNPs-lomefloxacin detection system is proved excellent by comparing with other ions and analytes in urine. The method in our study is appropriate to be used to monitor quantitatively entecavir in human urine owing to its rapid response rate, visible color changes, wide linear range and excellent selectivity.

Highly sensitive and selective electrochemical detection of Hg(2+) through surface-initiated enzymatic polymerization

A Hg(2+) electrochemical biosensor is developed by integrating thymine-Hg(2+)-thymine (T-Hg(2+)-T) base pairs for the high selectivity with surface-initiated enzymatic polymerization (SIEP) for signal amplification. The fabrication begins with the covalent conjugation of capture DNA probe labeled with thiol at its 3'terminal onto the gold electrode. The presence of Hg(2+) leads to DNA hybridization, in which complementary DNA was captured onto the biosensor surface, which subsequently catalyzed the addition of deoxynucleotides (dNTP) containing biotinlated 2'-deoxyadenosine 5'-triphosphate (biotin-dATP) by terminal deoxynucleotidyl transferase (TdT). The binding between biotin and strepavidin leads to the attachment of a large number of strepavidin functionalized silver nanoparticles (strepavidin-AgNPs), which could generate electrochemical stripping signal of silver to monitor the concentration of Hg(2+) in KCl solution. Through utilizing the T-Hg(2+)-T selectivity and SIEP amplification, this assay method can detect aqueous Hg(2+) with a wide linear range from 0.05 nM to 100 nM and a detection limit of 0.024 nM. The application of this sensor in the analysis of drinking water demonstrates that the proposed method works well for real samples.

Synergistic catalysis by gold nanoparticles and metal ions for enhanced chemiluminescence

The first report of individual and synergistic roles of alkali metal ions and gold nanoparticles in the enhancement of luminol-Urea–H₂O₂ chemiluminescence. A maximum of 600% increase over control was evident for NaCl in synergy with gold nanoparticles.

Highly sensitive homogenous chemiluminescence immunoassay using gold nanoparticles as label

Homogeneous immunoassay is becoming more and more attractive for modern medical diagnosis because it is superior to heterogeneous immunoassay in sample and reagent consumption, analysis time, portability and disposability. Herein, a universal platform for homogeneous immunoassay, using human immunoglobulin G (IgG) as a model analyte, has been developed. This assay relies upon the catalytic activity of gold nanoparticles (AuNPs) on luminol-AgNO3 chemiluminescence (CL) reaction. The immunoreaction of antigen and antibody can induce the aggregation of antibody-functionalized AuNPs, and after aggregation the catalytic activity of AuNPs on luminol-AgNO3 CL reaction is greatly enhanced. Without any separation steps, a CL signal is generated upon addition of a trigger solution, and the CL intensity is directly correlated to the quantity of IgG. The detection limit of IgG was estimated to be as low as 3pg/mL, and the sensitivity was better than that of the reported AuNPs-based CL immunoassay for IgG.

Effect of aggregated silver nanoparticles on luminol chemiluminescence system and its analytical application

We found that after silver nanoparticles (AgNPs) aggregated, its catalytic activity on luminol CL reaction obviously changed, and the change characteristic was closely related to the sizes of AgNPs. UV-visible spectra, X-ray photoelectron spectra, zeta potential and transmission electron microscopy studies were carried out to investigate the CL effect mechanism. The different CL responses of aggregated AgNPs with different size were suggested to be due to the two effects of quantum size and electron density in nanoparticle's conduction bands, and which one played a major role. The poisonous organic contaminants such as anilines, could induce the aggregation of AgNPs, were observed to affect effectively the luminol-H2O2-7 nm and 15 nm AgNPs CL systems and were detectable by use of a flow injection method with the enhanced or inhibited CL detection.

Label-free silver nanoparticles for the naked eye detection of entecavir

A simple, rapid, field-portable colorimetric method for the detection of entecavir was proposed based on the color change caused by the aggregation of silver nanoparticles. Neutralization of the electrostatic repulsion from each silver nanoparticle resulted in the aggregation of AgNPs and a consequent color change of AgNPs from yellow to wine-red, which provided a platform for rapid and field-portable colorimetric detection of entecavir. The concentration of entecavir could be determined with naked eye or UV-vis spectrometer. The proposed method can be used to detect entecavir in human urine with a detection limit of 1.51μg mL(-1), within 25min by naked eye observation without the aid of any advanced instrument or complex pretreatment. Results from UV-vis spectra showed that the absorption ratio was linear with the concentration of entecavir in the range of 5.04-25.2μg mL(-1) and 1.01-5.04μg mL(-1) with linear coefficients of 0.9907 and 0.9955, respectively. The selectivity of AgNPs detection system for entecavir is excellent comparing with other ions and analytes. Due to its rapid, visible color changes, and excellent selectivity, the AgNPs synthesized in this study are suitable to be applied to on-site screening of entecavir in human urine.

Amino acids as novel nucleophiles for silver nanoparticle-luminol chemiluminescence

The use of noble metal nanoparticles (NPs) as reductants in chemiluminescence (CL) has been reported only rarely owing to their high oxidation potentials. Interestingly, nucleophiles could dramatically lower the oxidation potential of Ag NPs, such that in the presence of nucleophiles Ag NPS could be used as reductants to induce the CL emission of luminol, an important CL reagent widely used in forensic analysis for the detection of trace amounts of blood. Although nucleophiles are indispensible in Ag NP-luminol CL, only inorganic nucleophiles such as Cl(-), Br(-), I(-) and S2O3 (2-) have been shown to be efficient. The effects of organic nucleophiles on CL remain unexplored. In this study, 20 standard amino acids were evaluated as novel organic nucleophiles in Ag NP-luminol CL. Histidine, lysine and arginine could initiate CL emission; the others could not. It is proposed that the different behaviors of 20 standard amino acids in the CL reactions derive from the interface chemistry between Ag NPs and these amino acids. UV/vis absorption spectra were studied to validate the interface chemistry. In addition, imidazole and histidine were chosen as a model pair to compare the behavior of the monodentate nucleophile with that of the corresponding multidentate nucleophile in Ag NP-luminol CL.

Conjugated polyelectrolytes-initiated chemiluminescence: a biosensing platform for label-free and homogeneous DNA detection

In this study, it was found that conjugated polyelectrolytes (CPEs) would initiate the strong chemiluminescence (CL) emission of luminol-H2O2 in weak basic media. Using CL spectra, ultraviolet visible light spectra, fluorescence spectra and electron spin resonance (ESR) spectra, the catalytic mechanism of CPEs on luminol-H2O2 CL was discussed in detail. Furthermore, it was found that the catalytic activity of poly [3-(3'-N,N,N-triethylamino-1'-propyloxy)-4-methyl-2,5-thiophene hydro chloride] (PMNT) (a kind of cationic CPEs) on the luminol-H2O2 CL system was closely relevant to the conformation of PMNT. The CL intensity of luminol-H2O2-PMNT system in the presence of single-stranded DNA was much larger than that in the presence of double-stranded DNA. By taking advantage of this phenomenon, a label-free and homogeneous CL detection of DNA hybridization is proposed. The detection limit of target DNA (3σ) was estimated to be as low as 3.7×10(-13)M. The present CL method for DNA hybridization detection offers the advantages of being simple, cheap, rapid and sensitive.