Synergistic Applications of Quantum Dots and Magnetic Nanomaterials in Pathogen Detection: A Comprehensive Review.

The rapid and accurate detection of pathogens is crucial for effective disease prevention and management in healthcare, food safety, and environmental monitoring. While conventional pathogen detection methods like culture-based techniques and PCR are sensitive and selective, they are often time-consuming, require skilled operators, and are not suitable for point-of-care or on-site testing. To address these limitations, innovative sensor technologies have emerged that leverage the unique properties of nanomaterials. Quantum dots (QDs) and magnetic nanomaterials are two classes of nanomaterials that have shown particular promise for pathogen sensing. This review comprehensively examines the synergistic applications of QDs and magnetic nanomaterials for detecting bacteria, viruses, phages, and parasites. .

A robust electrochemical sensing platform for the detection of erlotinib based on nitrogen-doped graphene quantum dots/copper nanoparticles-polyaniline-graphene oxide nanohybrid.

Erlotinib is a potent and highly specific tyrosine kinase inhibitor with the hindering effects on the growth of cancer cells. An electrochemical sensor with the great sensitivity and selectivity was fabricated for determining erlotinib by using a graphite rod electrode modified by the nitrogen-doped graphene quantum dots (N-GQDs) and a ternary nanohybrid comprising copper nanoparticles, polyaniline, along with graphene oxide (N-GQDs/CuNPs-PANI@GO) for the first time. The establishment of PANI and CuNPs was done simultaneously on the GO surface by thein situoxidative polymerization method. The morphological characteristics and elemental structure of the synthesized nanoparticles were examined by some microscopy techniques and x-ray energy/diffraction methods. The fabricated sensor represented the electrocatalytic activity towards erlotinib with a linear detection range from 1.0 nM to 35.0µM, a detection limit of 0.712 nM, and a sensitivity of 1.3604µAµM-1. Moreover, the N-GQDs/CuNPs-PANI@GO sensor showed acceptable stability up to 30 d (94.82%), reproducibility (RSD values of 3.19% intraday and 3.52% interday), and repeatability (RSD value of 3.65%) as a novel and powerful electrochemical sensor. It was successfully applied to monitor erlotinib in the drug-injected aqueous solution, serum, and urine samples that proved the capability of the sensor for the erlotinib monitoring in the biological samples.

Photocatalytic activity of green synthesized cadmium sulfide quantum dots on the removal of RhB dye and its cytotoxicity and antibacterial studies.

Presence of inorganic pollutants in water reservoirs is the treating factor for human health and environment. Semiconductor quantum dots (QDs) has been regarded as one of the most efficient nanoparticles for their enhanced photocatalytic activity. Medicinal plants are the safe sources to provide green template for biosynthesis of inorganic nanoparticles such as quantum dots. In order to determine the photocatalytic and biological application of cadmium sulfide quantum dots (CdS QDs), a biosynthesis approach was employed using saffron (Crocus sativus L.) stigma extract as the green reaction substrate. The biosynthesis process was evaluated at different pH condition to obtain the most efficient CdS QDs. Characterization of prepared CdS QDs were determined through UV-vis and fluorescence spectroscopy, FTIR and TEM analysis. The obtained results showed well dsispersed and uniform QDs during green synthesis at the optimum condition. The absorption and electrical properties of green synthesized CdS QDs showed the lowest energy bandgap of 2.4 at pH 11. Photocatalytic activity of CdS QDs on Rhodamine B degradation showed 92% degradation after 80 min under UV light irradiation. The antibacterial and cell cytotoxicity of green synthesized CdS QDs were assayed by disk diffusion and MTT assays respectively. Obtained results showed significant antibacterial effect of CdS QDs against gram-positive and gram-negative bacteria includingB. subtilis(90%) andE. coli(96%) respectively. Moreover, cytotoxicity of prepared CdS Qds through MTT assay indicated 79% apoptosis induction on MCF-7 breast cancer cells.

A novel colorimetric biosensor for sensitive detection of aflatoxin mediated by bacterial enzymatic reaction in saffron samples.

Aflatoxin is regarded as the potent carcinogenic agent which is secreted from fungi and present in some food products. So far, many detection methods have been developed to determine the trace amounts of aflatoxin in foods. In the present study a colorimetric competitive assay for detection of aflatoxin B1 (AFB1) has been developed based on interaction of gelatin functionalized gold nanoparticles (AuNPs@gelatin) in specific enzymatic reaction. Bacterial supernatant containing gelatinase enzyme were used as the substrate that could digest the coated gelatin on the surface of AuNPs and following in the presence of NaCl medium ingredient resulted to color change of AuNPs colloidal solution from red to purple. It was observed that with addition of aflatoxin to the bacterial supernatant, aflatoxin could interfere in aggregation of AuNPs and inhibited the process which subsequently prevent the expected color change induced by AuNPs aggregation. The supernatant containing AuNPs were investigated to analyze their induced surface plasmon resonance spectra through UV-visible spectroscopy. The absorption values were directly proportional with the applied AFB1 concentration. The experiment conditions including incubation time, AuNPs concentration and pH were investigated. The obtained results showed that through this approach we could detect the AFB1 in a linear range from 10 to 140 pg ml-1, with detection limit of 4 pg ml-1. Real sample assay in saffron samples showed recoveries percentage of 92.4%-95.3%. The applied approach proposed simple, cost effective and specific method for detection of AFB1 toxin in food samples.

A colorimetric assay of DNA methyltransferase activity based on peroxidase mimicking of DNA template Ag/Pt bimetallic nanoclusters.

DNA methylation catalyzed by DNA methyl transferase (MTase) is a significant epigenetic process for modulating gene expression. Abnormal levels of DNA MTase enzyme have been regarded as a cancer biomarker or a sign of bacterial diseases. We developed a novel colorimetric method to assay M.SssI MTase activity employing peroxidase-like activity of DNA template Ag/Pt NCs without using restriction enzymes. Based on inhibiting the peroxidase reaction that occurred in the TMB-H2O2 system, in the presence of MTase, a highly sensitive and selective colorimetric biosensor was fabricated with a detection limit (LOD) of 0.05 U/mL and a linear range from 0.5 to 10 U/mL. The changes in absorption intensity were monitored to quantify the M.SssI activity. This strategy had a high selectivity over other proteins. Furthermore, it is also demonstrated that this method can be used for the evaluation and screening of inhibitors for DNA MTase.

Study on the Interaction of the CpG Alternating DNA with CdTe Quantum Dots.

A novel sensitive method for detection of DNA methylation was developed with thioglycollic acid (TGA)-capped CdTe quantum dots (QDs) as fluorescence probes. Recognition of methylated DNA sites would be useful strategy due to the important roles of methylation in disease occurrence and developmental processes. DNA methylation occurs most often at cytosine-guanine sites (CpG dinucleotides) of gene promoters. The QDs significantly interacted with hybridized unmethylated and methylated DNA. The interaction of CpG rich methylated and unmethylated DNA hybrid with quantum dots as an optical probe has been investigated by fluorescence spectroscopy and electrophoresis assay. The fluorescence intensity of QDs was highly dependent to unmethylated and methylated DNA. Specific site of CpG islands of Adenomatous polyposis coli (APC), a well-studied tumor suppressor gene, was used as the detection target. Under optimum conditions, upon the addition of unmethylated dsDNA, the fluorescence intensity increased in linear range from 1.0 × 10- 10 to 1.0 × 10- 6M with detection limit of 6.2 × 10- 11 M and on the other hand, the intensity of QDs showed no changes with addition of methylated dsDNA. We also demonstrated that the unmethylated and methylated DNA and QDs complexes showed different mobility in electrophoresis assay. This easy and reliable method could distinguish between methylated and unmethylated DNA sequences.

Spectroscopic Study of CpG Alternating DNA-Methylene Blue Interaction for Methylation Detection.

Recognition of methylated DNA sites would be useful strategy due to the important roles of methylation in disease occurrence and developmental processes. The interaction of CpG rich methylated and unmethylated DNA hybrid with methylene blue (MB) as an optical probe has been investigated by absorption, emission, circular dichorism and fluorescence anisotropy analysis. Titration of MB with both sequences caused a hypsochromism and decreased the absorption of MB that indicating an intercalative mode of interaction. The experimental results revealed that MB as the optical indicator could distinguish between the methylated and unmethylated DNA sequences. Under optimum conditions, upon the addition of methylated dsDNA, the fluorescence intensity increased in linear range from 1.0 × 10(-9) to 1.0 × 10(-6) M with detection limit of 7.2 × 10(-10) M and on the other hand, the intensity of MB showed no change with addition of unmethylated dsDNA.

Rapid restriction enzyme free detection of DNA methyltransferase activity based on DNA-templated silver nanoclusters.

DNA methylation has significant roles in gene regulation. DNA methyltransferase (MTase) enzyme characterizes DNA methylation and also induces an aberrant methylation pattern that is related to many diseases, especially cancers. Thus, it is required to develop a method to detect the DNA MTase activity. In this study, we developed a new sensitive and reliable method for methyltransferase activity assay by employing DNA-templated silver nanoclusters (DNA/Ag NCs) without using restriction enzymes. The Ag NCs have been utilized for the determination of M.SssI MTase activity and its inhibition. We designed an oligonucleotide probe which contained an inserted six-cytosine loop as Ag NCs formation template. The changes in fluorescence intensity were monitored to quantify the M.SssI activity. The fluorescence spectra showed a linear decrease in the range of 0.4 to 20 U/ml with a detection limit of 0.1 U/ml, which was significant compared with previous reports. The proposed method was applied successfully for demonstrating the Gentamicin effect as MTase inhibitor. The proposed method showed convenient reproducibility and sensitivity indicating its potential for the determination of methyltransferase activity.

A Novel Label-Free microRNA-155 Detection on the Basis of Fluorescent Silver Nanoclusters.

In this paper, a new approach for microRNA-155 (miRNA-155) detection was described based on the fluorescence quenching of oligonucleotide-templated silver nanoclusters (DNA-AgNCs). The specific DNA scaffold with two different nucleotides fragments were used: one was enriched with a cytosine sequence fragment (C12) that could result in DNA-AgNCs with a high quantum yield via a chemical reduction method, and the other was the probe fragment (5- CUGUUAAUGCUAAUCGUG-3) which could selectively bind to the miRNA-155. Thus, the as-prepared AgNCs could exhibit quenched fluorescence when binding to the target miRNA-155. The fluorescence ratio of the DNA-AgNCs was quenched in a linearly proportional manner to the concentration of the target in the range of 0.2 nM to 30 nM with a detection limit of 0.1 nM.

Aptamer-based Colorimetric and Chemiluminescence Detection of Aflatoxin B1 in Foods Samples.

We developed a new biosensor for the detection of aflatoxin B1(AFB1) based on the interaction of gold nanoparticles (AuNPs) with the aptamer. Aggregation of AuNPs was induced by desorption of the AFB1 binding aptamer from the surface of AuNPs as a result of the aptamer target interaction leading to the color change of AuNPs from red to purple. The linear range of the colorimetric aptasensor covered a large variation of AFB1 concentrations from 80 to 270 nM and the detection limit of 7 nM was obtained. Also, the catalytic activity of the aggregated AuNPs greatly enhanced the chemiluminescence (CL) reaction, where the detection limit was determined at 0.5 nM with a regression coefficient of R(2) = 0.9921. We have also shown that the sensitivity of detection was increased by employing CL and using the catalytic activity of aggregated AuNPs, during luminol-hydrogen peroxide reaction. Therefore the proposed nanobiosensor was demonstrated to be sensitive, selective, and simple, introducing a viable alternative for rapid screening of toxin in foods.

Encapsulation of Lactiplantibacillus plantarum probiotics through cross-linked chitosan and casein for improving their viability, antioxidant and detoxification.

In the present study, encapsulation of Lactiplantibacillus plantarum (L.p) was performed using chitosan and casein through calcium phosphate intercrossing. Chitosan and casein both considered as non-toxic and biocompatible food derived components with intrinsic antioxidant properties. Layer by layer strategy was performed for deposition of modified cross-linked chitosan along with casein as the novel protective layers on the surface of probiotics. After confirmation of successful encapsulation, the viability and antioxidant activity of encapsulated L.p was evaluated. The results showed enhanced survival and antioxidant activity of encapsulated L.p compared to free bacteria in simulated digestive conditions. The survival of free and encapsulated L.p was respectively 1.38 ± 0.29 log cfu/ml and 6.99 ± 0.12 log cfu/ml in SGF and 8.54 ± 0.05 log cfu/ml and 7.25 ± 0.23 log cfu/ml in SIJ after 2 h of incubation. HPLC analysis was also used to investigate the detoxification activity of probiotics toward Aflatoxin M1 and obtained results showed encapsulated bacteria could significantly reduce aflatoxin M1 (68.44 ± 0.5 %) compared to free bacteria (43.76 ± 0.54 %). The results of this research suggest that the chitosan/casein mediated encapsulation of L.p with layer-by-layer technology is an effective method to improve the survival and antioxidant properties of probiotics with enhanced detoxification of AFM1.

A biosensor integrating the electrochemical and fluorescence strategies for detection of aflatoxin B1 based on a dual-functionalized platform.

BACKGROUND: Aflatoxin B1 (AFB1), is a potent hepatic carcinogen which causes cancer by inducing DNA changes in the liver cells. Variety of methods have been developed for detection of AFB1 which are based on single mode detection strategy. Fabrication of novel platform which are compatible for multimodal detection of AFB1 provide robust performance for reliable detection of AFB1. In this study, we aimed to develop a robust biosensing platform that combines electrochemical and fluorescence techniques for the sensitive and specific detection of Aflatoxin B1. RESULTS: The sensing platform includes the magnetic core-shell Fe3O4@AuNPs and zeolitic imidazolate framework-8 (ZIF-8). In electrochemical mode, the applied voltametric approach was used through functionalization of glassy carbon electrode and exhibited a linear range between 0.5 and 10000 pg mL-1 with LOD of 0.32 pg mL-1. Fluorescence analysis was based on the FRET on/off status of FAM-functionalized aptamer deposited on the same platform. The FAM emission recovered by the addition of AFB1 concentration in the range of 6-60 fg mL-1 with the LOD of 0.20 fg mL-1. The real sample analysis demonstrated satisfactory relative recoveries in the range of 92.81-105.32 % and 91.66-106.66 % using the electrochemical and fluorescence methods, respectively, and its reliability was confirmed by the HPLC technique. SIGNIFICANCE: The experimental results affirm that the proposed aptasensor serves as a sensitive, efficient, and precise platform for monitoring AFB1 in both electrochemical and fluorescence detection approaches. Proposed strategy showed efficient selectivity among different analytes and was reproducible. Furthermore, the applicability of biosensor was confirmed in food and biological samples.

Dual mode fluorometric and colorimetric detection of matrix metalloproteinase MMP-9 as a cancer biomarker based on AuNPs@gelatin/AuNCs nanocomposite.

Matrix metalloproteinase (MMPs) are proteolytic enzymes which considered as important enzymes and their higher expression is associated with some malignant progression. In the present study, a novel and sensitive method was developed for detection of MMP-9 based on its gelatinase activity. Green emitting gold nanoclusters (AuNCs) has been synthesized by gelatin substrate and then AuNPs@gelatin/AuNCs nanocomposite structure were prepared through coating of gold nanoparticles (AuNPs) with gelatin/AuNCs. Characterization and morphology of synthesized nanocomposite showed successful formation of AuNPs@gelatin/AuNCs. Constructed nanocomposite exhibited internal FRET occurrence and fluorescence quenching of AuNCs due to proximity of AuNCs/AuNPs structures. Hydrolysis effect of MMPs enzyme on AuNPs@gelatin/AuNCs in saline buffer induced changes in surface plasmon resonance (SPR) of gold nanoparticles and also enhanced the emitted fluorescence by AuNCs due to inhibition of internal FRET process. The proposed platform served as the efficient approach for semi-quantitative detection of MMP-9 enzyme by naked eye and precise activity detection with LOD of 2 ng/mL calorimetrically and 0.25 ng/mL fluorometrically. The approach was also showed convenient recovery for detection of MMP-9 enzyme in human serum matrix. Our work provides an efficient, convenient and practical tool for simple identification and precise detection of MMP-9 enzyme.

A simple smartphone-assisted paper-based colorimetric biosensor for the detection of urea adulteration in milk based on an environment-friendly pH-sensitive nanocomposite.

Urea is a common milk adulterant that falsely increases its protein content. Excessive consumption of urea is harmful to the kidney, liver, and gastrointestinal system. The conventional methods for urea detection in milk are time-consuming, costly, and require highly skilled operators. So, there is an increasing demand for the development of rapid, convenient, and cost-efficient methods for the detection of urea adulteration in milk. Herein, we report a novel colorimetric paper-based urea biosensor, consisting of a novel environment-friendly nanocomposite of halloysite nanotubes (HNT), that urease enzyme and an anthocyanin-rich extract, as a natural pH indicator are simultaneously immobilized into its internal and external surfaces. The biosensing mechanism of this biosensor is based on anthocyanin color change, which occurs due to urease-mediated hydrolysis of urea and pH increment of the environment. The colorimetric signal of this biosensor is measured through smartphone-assisted analysis of the mean RGB (Red-Green-Blue) intensity of samples and is capable of detecting urea with a detection limit of 0.2 mM, and a linear range from 0.5 to 100 mM. This biosensor has demonstrated promising results for the detection of urea in milk samples, in the presence of other milk adulterants and interferents.

A stem-loop like aptasensor for sensitive detection of aflatoxin based on graphene oxide/AuNPs nanocomposite platform.

Aflatoxin as the potent carcinogenic mycotoxin had been received great attention for detection in food industry and safety. Due to low quantity of aflatoxin in food samples, there is a need to develop a sensitive method toward its detection. In the present study, an aflatoxin B1 (AFB1) specific aptasensor with internal complementary sequence was developed for detection of AFB1. The FAM-functionalized aptamer was deposited on the surface of graphene oxide decorated with gold nanoparticles (GO/AuNPs) and following formation of heteroduplex stem-loop structure led to fluorescence quenching of FAM-labeled aptamer. After incubation of proposed aptasensor with AFB1, the aptamer-AFB1 complex resulted to denaturation in stem-loop structure of aptamer which caused restoration of single strand aptamer and recovery of fluorescence. The assay showed a convenient detection response in the range of 0.5-20 pg/mL with a very low detection limit (0.1 pg/mL) and it was highly selective for AFB1 over other mycotoxins.

Paper-based colorimetric detection of COVID-19 using aptasenor based on biomimetic peroxidase like activity of ChF/ZnO/CNT nano-hybrid.

Corona Virus Disease 2019 (COVID-19) as the infectious disease caused the pandemic disease around the world through infection by SARS-CoV-2 virus. The common diagnosis approach is Quantitative RT-PCR (qRT-PCR) which is time consuming and labor intensive. In the present study a novel colorimetric aptasensor was developed based on intrinsic catalytic activity of chitosan film embedded with ZnO/CNT (ChF/ZnO/CNT) on 3,3',5,5'-tetramethylbenzidine (TMB) substrate. The main nanocomposite platform was constructed and functionalized with specific COVID-19 aptamer. The construction subjected with TMB substrate and H2O2 in the presence of different concentration of COVID-19 virus. Separation of aptamer after binding with virus particles declined the nanozyme activity. Upon addition of virus concentration, the peroxidase like activity of developed platform and colorimetric signals of oxidized TMB decreased gradually. Under optimal conditions the nanozyme could detect the virus in the linear range of 1-500 pg mL and LOD of 0.05 pg mL. Also, a paper-based platform was used for set up the strategy on applicable device. The paper-based strategy showed a linear range between 50 and 500 pg mL with LOD of 8 pg mL. The applied paper based colorimetric strategy showed reliable results for sensitive and selective detection of COVID-19 virus with the cost-effective approach.

Facile fabrication of ternary MWCNTs/ZnO/Chitosan nanocomposite for enhanced photocatalytic degradation of methylene blue and antibacterial activity.

Developing a cheap, stable and effective photocatalyst is necessary for remediation of persistent organic pollutants. To address this challenge, we proposed a unique interfacial engineering technique and proper bandgap matching strategy to synthesize MWCNTs/ZnO/Chitosan ternary nanocomposite for effective photocatalytic application. The features of the prepared samples were determined by FESEM, TEM, EDX, elemental mapping, AFM, FT-IR, XRD, UV-Vis spectroscopy and BET surface analysis. The obtained results showed successful fabrication of synthesized nanocomposites with enhanced surface area. Degradation effect of nanostructures on methylene blue (MB) and antibacterial activity against Escherichia coli (E. coli), Staphylococcus aureus (S. aureus) and Bacillus subtilis (B. subtilis) pathogenic strains were investigated. The proposed photocatalytic mechanism illustrated the electron transfer facilitated by MWCNTs/ZnO/Chitosan structure which results in spatial separation of electron-hole pairs. Compared with ZnO and ZnO/Chitosan, the prepared MWCNTs/ZnO/Chitosan ternary nanocomposite showed high usage of UV illumination and superior separation of photogenerated electron-hole pairs. MWCNTs/ZnO/Chitosan illustrated 86.26% adsorption rate and outstanding increased photocatalytic activity on MB degradation efficiency of 98.76% after 20 min. Stability of photocatalyst reached from 98.76% initial decolorization to 85% at the fourth cycle. In addition, the ternary nanocomposite also exhibited remarkable bactericidal activity against gram-positive (S. aureus) and (B. subtilis) and gram-negative (E. coli) bacteria strains. Due to the obtained results, the prepared nanocomposite would be an efficient candidate photocatalyst with antibacterial properties.

Fluorometric detection of phytase enzyme activity and phosphate ion based on gelatin supported silver nanoclusters.

Phytase is the commercial enzyme for bioconversion of phytate substrate to digestible phosphate ions. Recently silver nanoclusters (AgNCs) have received great attention as the optical transducer nanoparticles in biosensors structure. The novel detection platform was developed to detect the phytase enzyme activity and phosphate ions based on fluorescence quenching of AgNCs. The AgNCs were synthesized through gelatin supported reaction and characterized by TEM, FTIR and XRD analysis. The hydrolytic effect of phytase enzyme and subsequent phosphate release led to suppression of AgNCs fluorescence. The linear range was observed for enzyme in the range of 0.5-5 U/mL with the detection limit of 0.2 U/mL. Also, the same fluorescence quenching effect was observed in the presence of phosphate ion in the linear range of 1 to 16 µM with a detection limit of 0.5 µM. The proposed mechanism showed effectiveness of detection strategy for detection of phytase enzyme and phosphate ion.

Fabrication of Graphene-Based TiO2@CeO2 and CeO2@TiO2 Core-Shell Heterostructures for Enhanced Photocatalytic Activity and Cytotoxicity.

Development of light-harvesting properties and inhibition of photogenerated charge carrier recombination are of paramount significance in the photocatalytic process. In the present work, we described the synthesis of core-shell heterostructures, which are composed of titanium oxide (TiO2) and cerium oxide (CeO2) deposited on a reduced graphene oxide (rGO) surface as a conductive substrate. Following the synthesis of ternary rGO-CeO2@TiO2 and rGO-TiO2@CeO2 nanostructures, their photocatalytic activity was investigated toward the degradation of rhodamine B dye as an organic pollutant under UV light irradiation. The obtained structures were characterized with high-resolution transmission electron microscopy, field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction, Brunauer-Emmett-Teller, X-ray photoelectron spectroscopy surface analysis, and UV-Vis spectroscopy. Various parameters including pH, catalyst dosage, temperature, and contact time were studied for photocatalysis optimization. Heterostructures showed considerable advantages because of their high surface area and superior photocatalytic performance. In contrast, rGO-CeO2@TiO2 showed the highest photocatalytic activity, which is attributed to the more effective electron-hole separation and quick suppression of charge recombination at core-shell phases. A biological assay of the prepared heterostructure was performed to determine the cytotoxicity against breast cancer cells (MCF-7) and demonstrated a very low survival rate at 7.65% of cells at the 17.5 mg mL-1 concentration of applied photocatalyst.

Colorimetric and label free detection of gelatinase positive bacteria and gelatinase activity based on aggregation and dissolution of gold nanoparticles.

A simple and sensitive method was developed for the detection of bacteria gelatinase activity based on their enzymatic hydrolysis effect on the surface plasmon resonance (SPR) of gelatin functionalized gold nanoparticles (Au@gelatin NPs) in bacteria supernatant. Characterization of synthesized NPs showed a very thin gelatin layer on the surface of about 20 nm AuNPs which modified the intrinsic SPR property of AuNPs. The extracted supernatants of applied bacteria were incubated with Au@gelatin NPs. Gelatinase activity of bacteria resulted in gradual gelatin shell removal and subsequent dissolution of bare AuNPs. The presence of inducer agents such as NaCl as the common ingredient in the bacterial medium led to the aggregation process of AuNPs and further bacterial activity resulted in AuNPs dissolution. AuNPs colloid solution color was changed from red to purple after addition of bacteria supernatants with gelatinase activity to the reaction. Also, the spectroscopic studies showed that the gelatinase activity of bacteria resulted in the gradual decrease of absorbance at 529 nm and subsequently led to extinction of SPR characteristics. So, the observed absorbance decrease in UV-Vis spectra at 529 nm was indicated as the gelatinase activity of applied bacteria. Different strains of gelatinase positive Bacillus strains were used as the real sample and their gelatinase activity was determined in the present study. Also, sensitivity analysis of the applied method was determined through this method and the obtained results showed Bacillus subtilis gelatinase activity in the linear range of 0-120 U/mL and detection limit of 0.5 U/mL. This method introduced label free, facile and sensitive assay of the bacterial gelatinase activity without any complicated instrument, affording convenience and simplicity.