Synthesis and Characterization of Eugenia uniflora L. Silver Nanoparticles and L-Cysteine Sensor Application.

L-Cysteine (Cys) is a non-essential sulfur-containing amino acid, crucial for protein synthesis, detoxification, and several metabolic functions. Cys is widely used in the agricultural, food, cosmetic, and pharmaceutical industries. So, a suitable sensitive and selective sensing approach is of great interest, and a low-cost sensor would be necessary. This article presents silver nanoparticles (EuAgNPs) synthesized by a green synthesis method using Eugenia uniflora L. extracts and photoreduction. The nanoparticles were characterized by UV/VIS, transmission electron microscopy, high-performance liquid chromatography (HPLC), FTIR, and Zeta potential. With the addition of Cys in the EuAgNPs solution, the terminal thiol part of L-cysteine binds on the surface of nanoparticles through Ag-S bond. The EuAgNPs and CysAgNPs coexist until flavonoids bound the amino group of Cys, enhancing the red color of solutions. The EuAgNPs provided selectivity to detect Cys among other amino acids, and its detection limit was found to be 3.8 nM. The sensor has the advantages of low-cost synthesis, fast response, high selectivity, and sensitivity.

Antimicrobial Activity of Silver and Gold Nanoparticles Prepared by Photoreduction Process with Leaves and Fruit Extracts of Plinia cauliflora and Punica granatum.

The increased number of resistant microbes generates a search for new antibiotic methods. Metallic nanoparticles have emerged as a new platform against several microorganisms. The nanoparticles can damage the bacteria membrane and DNA by oxidative stress. The photoreduction process is a clean and low-cost method for obtaining silver and gold nanoparticles. This work describes two original insights: (1) the use of extracts of leaves and fruits from a Brazilian plant Plinia cauliflora, compared with a well know plant Punica granatum, and (2) the use of phytochemicals as stabilizing agents in the photoreduction process. The prepared nanoparticles were characterized by UV-vis, FTIR, transmission electron microscopy, and Zeta potential. The antimicrobial activity of nanoparticles was obtained with Gram-negative and Gram-positive bacteria, particularly the pathogens Staphylococcus aureus ATCC 25923; Bacillus subtilis ATCC 6633; clinical isolates of methicillin-resistant Staphylococcus aureus (MRSA) and Enterococcus faecalis; Escherichia coli ATCC 25922; Escherichia coli O44:H18 EAEC042 (clinical isolate); Klebsiella pneumoniae ATCC 700603, Salmonella Thiphymurium ATCC 10231; Pseudomonas aeruginosa ATCC 27853; and Candida albicans ATCC 10231. Excellent synthesis results were obtained. The AgNPs exhibited antimicrobial activities against Gram-negative and Gram-positive bacteria and yeast (80-100%), better than AuNPs (0-87.92%), and may have the potential to be used as antimicrobial agents.

Porphyrins are increased in the faeces of patients with prostate cancer: a case-control study.

BACKGROUND: Experimental models of prostate cancer have demonstrated increased levels of protoporphyrin IX (PpIX) in the blood and faeces of mice. Hence, the quantification of these autofluorescent molecules could be hypothesized to be a potential marker for this type of tumour. In this case-control study, the autofluorescence of porphyrins in human faeces from patients with prostate cancer and control subjects was analysed using fluorescence spectroscopy. METHODS: First, 3 mL of analytical-grade acetone was added to 0.3 g of faeces, and the mixture was macerated and centrifuged at 4000 rpm for 15 min. The supernatant was analysed spectroscopically. The emission spectra from 550 to 750 nm were obtained by exciting the samples at 405 nm. RESULTS: A significant difference between the samples from control and cancer subjects was established in the spectral region of 670-675 nm (p = 0.000127), which corresponds to a significant increase in faecal porphyrins in patients with cancer. There was no statistically significant correlation between PSA levels and faecal porphyrins. CONCLUSION: In this preliminary study conducted in humans, the results show a simple and non-invasive method to assess faecal porphyrins, which have the potential to function as a tumour biomarker in patients with prostate cancer. This approach has improved sensitivity and specificity over PSA testing. Additional prospective studies with larger sample sizes are required to validate these findings.

Biocompatible silver nanoparticles prepared with amino acids and a green method.

The synthesis of nanoparticles is usually carried out by chemical reduction, which is effective but uses many toxic substances, making the process potentially harmful to the environment. Hence, as part of the search for environmentally friendly or green synthetic methods, this study aimed to produce silver nanoparticles (AgNPs) using only AgNO3, Milli-Q water, white light from a xenon lamp (Xe) and amino acids. Nanoparticles were synthetized using 21 amino acids, and the shapes and sizes of the resultant nanoparticles were evaluated. The products were characterized by UV-Vis, zeta potential measurements and transmission electron microscopy. The synthesis of silver nanoparticles with tryptophan and tyrosine, methionine, cystine and histidine was possible through photoreduction method. Spherical nanoparticles were produced, with sizes ranging from 15 to 30 nm. Tryptophan does not require illumination nor heating, and the solution color changes immediately after the mixing of reagents if sodium hydroxide is added to the solution (pH = 10). The Xe illumination acts as sodium hydroxide in the nanoparticles synthesis, releases H+ and allows the reduction of silver ions (Ag+) in metallic silver (Ag0).

Aminolevulinic acid with gold nanoparticles: a novel theranostic agent for atherosclerosis.

In this study, 5-aminolevulinic acid (ALA) gold nanoparticles (ALA:AuNPs) functionalized with polyethylene glycol (PEG) were synthesized and administered to rabbits to evaluate their use in clinical practice as theranostic agents for atherosclerosis. This was done by measuring the porphyrin fluorescence extracted from the rabbits' blood and feces. An increase in blood and feces porphyrin emission after ALA:AuNP administration suggests that ALA was incorporated by gold nanoparticles, its structure was preserved, and a rapid conversion into endogenous porphyrins occurred, overloading the synthetic pathway that led to protoporphyrin IX (PPIX) accumulation. This finding indicated that this method can aid in the early diagnosis and therapy of atherosclerosis with high sensitivity.

Expression of Genes Involved in Porphyrin Biosynthesis Pathway in the Human Renal Cell Carcinoma.

Renal cell carcinoma (RCC) remains one of the greatest challenges of urological oncology and is the third leading cause of death in genitourinary cancers. Surgery may be curative when patients present with localized disease. Our previous results demonstrated the autofluorescence of blood PpIX in primary RCC mouse model and an increase in fluorescence intensity as a function of growth of the subcutaneous tumor mass. In another work, a nice correlation between the growth of the tumor mass and tissue fluorescence intensity was found. The aim of this study was to evaluate the expression profile of porphyrin biosynthesis pathway-related genes of human kidney cells. We used two kidney cell lines, one normal (HK2) and another malignant (Caki-1). Endogenous and 5-aminolevolinic acid (ALA) induced protoporphyrin IX (PpIX) HK2 and Caki-1 cells were analyzed by fluorescence spectroscopy. Real-time quantitative polymerase chain reaction (qRT-PCR) was used to measure mRNA of those genes. Emission spectra were obtained by exciting the samples at 405 nm. For ALA untreated cells the maximum fluorescence intensity was detected at 635 nm. The mean peak area of emission spectra in both cells types increased linearly in function of cell number. Besides, basal levels of PpIX autofluorescence of each cell concentration of HK2 samples were significantly lower than those of Caki-1 samples. For ALA-treated cells the mean PpIX spectra shows PpIX emission peak at 635 nm with a shoulder at 700 nm. Analysis of PpIX fluorescence intensity ratio between tumor cells and HK2 cells showed that fluorescence intensity was, on average, 26 times greater in tumor cells than in healthy cells. qRT-PCR revealed that in Caki-1 ALA-treated cells, PEPT gene was significantly up-regulated and FECH and HO-1 genes were significantly down regulated in comparison with HK2 ALA-treated cells. In conclusion, our results demonstrate the preferential accumulation of ALA-induced PpIX in human RCC and also indicate that PEPT1, FECH and HO-1 genes are major contributors to this accumulation.

Liquid biopsy of atherosclerosis using protoporphyrin IX as a biomarker.

Protoporphyrin IX (PPIX), a derivative of hematoporphyrin, can accumulate in rapidly growing tissues, including tumors and atherosclerotic plaques. The objective of this study is to employ PPIX fluorescence to detect the changes in blood caused by the formation of atheromatous plaques in arteries; this measurement can function as a liquid biopsy. For this purpose twenty four rabbits were randomly divided into groups: control group (CG)--fed with a normal diet, and an experimental group (EG)--fed with a hypercholesterolemic diet (1% cholesterol). Blood samples were collected before (0 time) and after 22, 43, 64 days to measure biochemical factors. The aortas were removed after 22, 43 and 64 days to assess the atherosclerotic plaques. PPIX was extracted from the blood and fluorescence was measured in the 550-750 nm range from samples that were excited at 405 nm. Aminolevulinic acid (ALA) was administered intravenously to increase the PPIX fluorescence intensity in the arteries and consequently in the liquid biopsy of the atherosclerotic plaques. The results have shown that the PPIX fluorescence increased as the atheromatous plaques grew. The aorta fluorescence and the PPIX fluorescence increased in the animals in the experimental group that received ALA. PPIX that accumulates in atheromatous plaques transfers to the blood and can be analyzed by extracting porphyrin from total blood. Therefore, this method can aid in the early diagnosis of atherosclerosis with high sensitivity.

Evaluation of Steady-State and Time-Resolved Fluorescence Spectroscopy as a Method for Assessing the Impact of Photo-Oxidation on Refined Soybean Oils.

The type of material used in packaging, lighting, and storage time can impact food quality during storage. This study aimed to investigate the progress of photosensitized oxidation in refined soybean oil using steady-state and time-resolved fluorescence spectroscopy. The experiment was conducted through accelerated photo-oxidation with Light-Emitting Diode (LED) in samples stored for ten days at room temperature (26.0 ± 2.0 °C) in clear polyethylene terephthalate (PET) packaging of different colors and different transmission spectra in the UV and visible range. Emission spectra were obtained with excitation at 373, 405, and 500 nm, resulting in two main emission peaks: the first with maximum emission between 430 and 555 nm and the second at around 660 nm. Fluorescence decay curves were obtained with excitation at 340 and 405 nm. The results indicated that transparent PET bottles are not effective in protecting soybean oil from photosensitized oxidation under the studied conditions. Strong correlations were observed between fluorescence parameters and peroxide and conjugated diene values, indicators of lipid oxidation progress. Fluorescence spectroscopy has several advantages over traditional methods as it is a simple, fast, low-cost, and low-waste technique.

Eugenia uniflora L. Silver and Gold Nanoparticle Synthesis, Characterization, and Evaluation of the Photoreduction Process in Antimicrobial Activities.

Eugenia uniflora linnaeus, known as Brazilian cherry, is widely distributed in Brazil, Argentina, Uruguay, and Paraguay. E. uniflora L. extracts contain phenolic compounds, such as flavonoids, tannins, triterpenes, and sesquiterpenes. The antimicrobial action of essential oils has been attributed to their compositions of bioactive compounds, such as sesquiterpenes. In this paper, the fruit extract of E. uniflora was used to synthesize silver and gold nanoparticles. The nanoparticles were characterized by UV-Vis, transmission electron microscopy, elemental analysis, FTIR, and Zeta potential measurement. The silver and gold nanoparticles prepared with fruit extracts presented sizes of ~32 nm and 11 nm (diameter), respectively, and Zeta potentials of -22 mV and -14 mV. The antimicrobial tests were performed with Gram-negative and Gram-positive bacteria and Candida albicans. The growth inhibition of EuAgNPs prepared with and without photoreduction showed the important functional groups in the antimicrobial activity.

Synthesis, characterization, antimicrobial activity, and toxicity evaluation of aminolevulinic acid-silver and silver-iron nanoparticles for potential applications in agriculture.

Aminolevulinic acid (ALA) is considered one of the most critical plants growth regulators and essential precursors for chlorophyll biosynthesis; besides, its photodynamic activity can be used to exterminate larvae and microorganisms in plants and soil. Silver nanoparticles (AgNPs) have unique physicochemical properties and potent antimicrobial, antiviral, and antifungal activities, and in agriculture, their application as nanopesticides has been proposed. In this study, silver and silver-iron nanoparticles capped/stabilized with aminolevulinic acid (ALAAgNPs and ALAAgFeNPs) were synthesized by the photoreduction method and characterized by UV-vis spectroscopy, transmission electron microscopy, and zeta potential analysis. The kinetics of 1O2 generation from ALAAgFeNPs were obtained. The ALANP toxicity was evaluated on stalks of E. densa by observing cell morphology changes and measuring chlorophyll content compared with water-treated plants. Antimicrobial activity was tested against E. coli, P. aeruginosa, and Candida albicans. The results suggested that ALANPs (prepared with [AgNO3] ≤ 0.2 mM and [ALA] ≤ 0.4 mM) could be suitable for applications in the agricultural sector. The presence of ∼0.3 mmol of iron in ALAAgNPs synthesis increased cell uptake and chlorophyll synthesis.

Application of fluorescence to the study of crude petroleum.

Crude petroleum oils are complex mixtures of different compounds (mainly organic), which are obtained from an extensive range of different geological sources. The fluorescence of crude petroleum oils derives largely from the aromatic hydrocarbon fraction, and this fluorescence emission is strongly influenced by the chemical composition (e.g., fluorophore and quencher concentrations) and physical characteristics (e.g., viscosity and optical density) of the oil. The fluorescence spectroscopy (FS) is increasingly used in petroleum technology due the availability of better optical detection techniques, because FS offers high sensitivity, good diagnostic potential, and relatively simple instrumentation. In this work we analyzed crude petroleum at different dilution in Nujol, a transparent mineral oil. The main objective of this work was to verify the possibility to measure crude oil emission spectroscopic without use of volatile solvents. The mixtures of nujol with different -crude oil concentrations were measured with a 10 mm optical path cuvette thus simplifying the fluorescence spectroscopy signal detection. The emission spectra were obtained by exciting the samples with a 400 W Xenon lamp at 350 nm, 450 nm and 532 nm. The emissions of the samples were collected perpendicularly with the excitation axis.

Investigation of the europium emission spectra of the europium-oxytetracycline complex in the presence of human low-density lipoproteins.

Low-Density Lipoprotein (LDL), often known as "bad cholesterol" is one of the responsible to increase the risk of coronary arterial diseases. For this reason, the cholesterol present in the LDL particle has become one of the main parameters to be quantified in routine clinical diagnosis. A number of tools are available to assess LDL particles and estimate the cholesterol concentration in the blood. The most common methods to quantify the LDL in the plasma are the density gradient ultracentrifugation and nuclear magnetic resonance (NMR). However, these techniques require special equipments and can take a long time to provide the results. In this paper, we report on the increase of the Europium emission in Europium-oxytetracycline complex aqueous solutions in the presence of LDL. This increase is proportional to the LDL concentration in the solution. This phenomenum can be used to develop a method to quantify the number of LDL particles in a sample. A comparison between the performances of the oxytetracycline and the tetracycline in the complexes is also made.

Characterization of chicken meat contaminated with Salmonella by fluorescence spectroscopy.

Contaminated poultry products as eggs and meat are the primary vehicles of Salmonella infection. Conventional methods for microorganisms detections involve multiple steps, and despite its accuracy, these assays are time-consuming. Biosensing methods have shown great potential for the rapid detection of foodborne pathogens. Some of the biosensors are based on fluorescence. Various fluorophores such as collagen, elastin, NAD(P)H, and porphyrins can be used to evaluate possible chemical changes in meat. In this manuscript, the fluorescence properties of chicken meat contaminated with Salmonella enterica (ATCC 14028) cell suspensions (500; 5000; 50,000 and 500,000 cells/mL) were obtained and compared with non-contaminated control, for meat kept at 25 °C for 24 and 48 h. The effects of ambient light were also considered. Our results indicated that free NAD(P)H and coproporphyrin emission bands present in contaminated meat, increased over time, and can provide access to valuable information for the detection of Salmonella in chicken meat.

SARS-CoV-2, hemoglobin and protoporphyrin IX: Interactions and perspectives.

BACKGROUND: SARS-CoV-2 attacks hemoglobin through its structural protein ORF3a, dissociating the iron from the heme, as iron is necessary by cell machinery for virus replication. In this process protoporphyrin (PpIX) is released. METHODS: The decrease in the hemoglobin levels observed in patients with Covid-19 is frequently accompanied by an increase in PpIX levels. This evidence was confirmed by the quantification of PpIX by high-performance liquid chromatography (HPLC). PpIX emission is observed in its two characteristic bands at approximately 635 nm and 705 nm. RESULTS: This paper searches to understand the role of heme and PpIX inside the cells. Perspectives on the use of PpIX fluorescence as a sensor to monitor the presence of SARS-CoV-2 in the tissue, blood, urine, or feces to map the evolution and severity of the disease or to monitor the response of the Covid-19 treatment modalities were described. CONCLUSION: Fluorescence spectroscopy could be adopted as an excellent diagnostic technique for Covid-19, of low cost and high sensitivity. This method can potentially be used as a marker to monitor the response to the treatments. Photodynamic and sonodynamic therapies using the endogenous PpIX increased in the acute phase of the disease, could be employed for Covid-19 treatment.

Study of the interactions of gold nanoparticles functionalized with aminolevulinic acid in membrane models.

Gold nanoparticles have been intensively studied in cancer therapy to improve drug release, increasing therapeutic action and reducing adverse effects. The interaction between gold nanoparticles and cell membranes can give information about the cell internalization. In this study, gold nanoparticles with aminolevulinic acid (5-ALA) were synthesized using the photoreduction method (5-ALA: AuNPs). The prodrug 5-ALA is responsible for protoporphyrin IX synthesis inside the cell and allows the use of therapies as photodynamic and sonodynamic therapies. The cytotoxicity test was performed on a breast cancer tumor line (MCF-7), and high Content Screening assay was applied to evaluate the entry of nanoparticles into cells. DPPS Langmuir monolayers were assembled at the air/water interface and employed as a simplified membrane model for half of a tumorigenic cell membrane. We assessed the molecular interactions between 5-ALA: AuNPs and phospholipids using tensiometry (π-A isotherms) and vibrational spectroscopy (PM-IRRAS) experiments. We found that the functionalized gold nanoparticles strongly interact with DPPS polar head groups (especially phosphate and carbonyl), changing the phospholipid hydration and leading to a general decrease in the monolayer conformational order. This work then probes that specific interaction between 5-ALA: AuNPs and the negatively charged phospholipid can be assessed using Langmuir monolayers as simplified biomembrane models.

Enhancement on the Europium emission band of Europium chlortetracycline complex in the presence of LDL.

Low-density lipoprotein (LDL) particles are the major cholesterol-carrying lipoprotein in the human circulation from the liver to peripheral tissues. High levels of LDL-Cholesterol (LDL-C) are known risk factor for the development of coronary artery disease (CAD). The most common approach to determine the LDL-C in the clinical laboratory involves the Friedewald formula. However, in certain situations, this approach is inadequate. In this paper we report on the enhancement on the Europium emission band of Europium chlortetracycline complex (CTEu) in the presence of LDL. The emission intensity at 615 nm of the CTEu increases with increasing amounts of LDL. This phenomenon allowed us to propose a method to determine the LDL concentration in a sample composed by an aqueous solution of LDL. With this result we obtained LDL calibration curve, LOD (limit of detection) of 0.49 mg/mL and SD (standard deviation) of 0.003. We observed that CTEu complex provides a wider dynamic concentration-range for LDL determination than that from Eu-tetracycline previously. The averaged emission lifetimes of the CTEu and CTEu with LDL (1.5 mg/mL) complexes were measured as 15 and 46 micros, respectively. Study with some metallic interferents is presented.

Intrinsic fluorescence of protoporphyrin IX from blood samples can yield information on the growth of prostate tumours.

Prostate cancer is one of the most common types of cancer in men, and unfortunately many prostate tumours remain asymptomatic until they reach advanced stages. Diagnosis is typically performed through Prostate-Specific Antigen (PSA) quantification, Digital Rectal Examination (DRE) and Transrectal Ultrasonography (TU). The antigen (PSA) is secreted by all prostatic epithelial cells and not exclusively by cancerous ones, so its concentration also increases in the presence of other prostatic diseases. DRE and TU are not reliable for early detection, when histological analysis of prostate tissue obtained from a biopsy is necessary. In this context, fluorescence techniques are very important for the diagnosis of cancer. In this paper we explore the potential of using endogenous phorphyrin blood fluorescence as tumour marker for prostate cancer. Substances such as porphyrin derivatives accumulate substantially more in tumours than in normal tissues; thus, measuring blood porphyrin concentration by autofluorescence intensity may provide a good parameter for determining tumour stage. In this study, the autofluorescence of blood porphyrin was analyzed using fluorescence and excitation spectroscopy on healthy male NUDE mice and in those with prostate cancer induced by inoculation of DU145 cells. A significant contrast between the blood of normal and cancer subjects could be established. Blood porphyrin fluorophore showed an enhancement on the fluorescence band around 632 nm following tumour growth. Fluorescence detection has advantages over other light-based investigation methods: high sensitivity, high speed and safety. However it does carry the drawback of low specificity of detection. The extraction of blood porphyrin using acetone can solve this problem, since optical excitation of further molecular species can be excluded, and light scattering from blood samples is negligible.

Erythrocyte protoporphyrin fluorescence as a biomarker for monitoring antiangiogenic cancer therapy.

Renal cell carcinoma (RCC) remains one of the greatest challenges of urological oncology and is the third leading cause of death in genitourinary cancers. RCCs are highly vascularized and are amenable to antiangiogenic therapy. Endostatin (ES) is a fragment of collagen XVIII that possesses antiangiogenic activity. In this study, we examined the potential of erythrocyte PpIX fluorescence spectroscopy for monitoring the efficacy of antiangiogenic therapy in metastatic renal cell carcinoma (mRCC), using an orthotopic metastatic mouse model. Balb/C-bearing Renca cells were treated with NIH/3T3-LendSN cells. Lung weight, nodule area, microvascular area (MVA), and erythrocyte PpIX fluorescence were evaluated. Emission spectra were obtained by exciting the samples at 405 nm. There was a significant decrease in lung wet weight, lung nodule area and MVA in the treated group compared to the control group (P < 0.001). Significant differences in autofluorescence shape were observed in the 620-650 nm spectral region. The most intense fluorescence peak was observed at ∼632 nm. The autofluorescence of the control samples was about 53% higher than that of normal blood (P < 0.05). In the group treated with ES, the autofluorescence was about 54% lower than in the control group (P < 0.05). Fluorescence intensity was positively correlated with the nodule area (R (2) = 0.8859; P < 0.001) and MVA (R (2) = 0.9431; P < 0.001) in the ES-treated group. These results demonstrate that the spectroscopic analysis method allows a selective detection of tumor masses. This preliminary study suggests that PpIX fluorescence may be useful as a biomarker for antiangiogenic cancer therapy.

Uptake of silver, gold, and hybrids silver-iron, gold-iron and silver-gold aminolevulinic acid nanoparticles by MCF-7 breast cancer cells.

BACKGROUND: Nanoparticles show promise for theranostic applications in cancer. The metal-based nanoparticles can be used both as photosensitizers and delivery vehicles. In bimetallic particles based on gold or silver and iron, a combination of the plasmonic features of the gold or silver components with the magnetic properties of the iron makes these hybrid nanomaterials suitable for both imaging and therapeutic applications. Herein, we discuss toxicity and cell internalization of metallic (silver and gold) and bimetallic (silver-iron, gold-iron, and silver-gold) aminolevulinic acid (ALA) nanoparticles. ALA can control the production of an intracellular photosensitizer, protoporphyrin IX (PpIX), commonly used in photodynamic therapy. METHODS: Nanoparticles were synthesized by photoreduction method and characterized by UV/Vis spectra, Zeta potential, FTIR, XRD, and transmission electron microscopy. The amount of singlet oxygen generation by a yellow LED, and ultrasound was studied for gold, gold-iron, and silver-gold nanoparticles. Cytotoxicity assays of MCF-7 in the presence of nanoparticles were performed, and PpIX fluorescence was quantified by high content screening (HCS). RESULTS: Red fluorescence observed after 24 h of nanoparticles incubation on MCF-7 cells, indicated that the ALA in surface of nanoparticles was efficiently converted to PpIX. The best results for singlet oxygen generation with LED or ultrasound irradiation were obtained with ALA:AgAuNPs. CONCLUSIONS: The studied nanoparticles present the potential to deliver aminolevulinic acid to breast cancer cells efficiently, generate singlet oxygen, and convert ALA into PpIX inside the cells allowing photodiagnosis and therapies such as photodynamic and sonodynamic therapies.

Optical properties of metacycline, oxytetracycline and chlortetracycline europium complexes in the presence of hydrogen peroxide.

Tetracycline possesses a great tendency to form complexes with a number of chemical species, particularly with Eu3+ ions. In this work we investigate the europium optical properties of three tetracyclines europium complexes: Metacycline (MTc), Oxytetracycline (OTc), and Chlortetracycline (CTc), in the presence and absence of hydrogen peroxide (HP). The results show that the emission band of EuOTc have enhancement in the presence of hydrogen peroxide. A calibration curve was shown for this complex with the best molar ratio obtained.