Carrageenan/agar-based functional film integrated with zinc sulfide nanoparticles and Pickering emulsion of tea tree essential oil for active packaging applications.

A functional carrageenan/agar-based film was prepared by combining tea tree oil Pickering emulsion (PET) and zinc sulfide nanoparticles (ZnSNP). PET was formulated using tea tree essential oil stabilized with nanocellulose fibers. PET and ZnSNPs were uniformly dispersed in the binary polymer matrix and formed compatible films. The incorporation of ZnSNPs improved the mechanical strength, whereas PET slightly decreased the strength, but the combined addition of ZnSNP and PET maintained the mechanical strength with slightly improved flexibility. The addition of ZnSNP and PET, alone or in combination, slightly improved the water vapor barrier, water resistance, and thermal stability of the film. In addition, the carrageenan/agar-based composite membrane showed distinct antioxidant and antibacterial activity. The ZnSNP and PET incorporated binary composite films with enhanced physical and functional properties are likely to be used in active food packaging applications.

New Active Packaging Based on Biopolymeric Mixture Added with Bacteriocin as Active Compound.

The objective of this work was to develop a chitosan/agar-agar bioplastic film incorporated with bacteriocin that presents active potential when used as food packaging. The formulation of the film solution was determined from an experimental design, through the optimization using the desirability function. After establishing the concentrations of the biopolymers and the plasticizer, the purified bacteriocin extract of Lactobacillus sakei was added, which acts as an antibacterial agent. The films were characterized through physical, chemical, mechanical, barrier, and microbiological analyses. The mechanical properties and water vapor permeability were not altered by the addition of the extract. The swelling property decreased with the addition of the extract and the solubility increased, however, the film remained intact when in contact with the food, thus allowing an efficient barrier. Visible light protection was improved by increased opacity and antibacterial capacity was effective. When used as Minas Frescal cream cheese packaging, it contributed to the increase of microbiological stability, showing a reduction of 2.62 log UFC/g, contributing a gradual release of the active compound into the food during the storage time. The film had an active capacity that could be used as a barrier to the food, allowing it to be safely packaged.

Simple stain-free screening method for pectinolytic microorganisms under alkalophilic conditions.

OBJECTIVES: To develop a simple pectin-degrading microorganism screening method. RESULTS: We developed a method utilizing the phenomenon whereby cooling an alkaline agar medium containing pectin causes the agar to become cloudy. This highly simplified method involves culturing the microorganisms on pectin-containing agar medium until colony formation is observed, and subsequent overnight cooling of the agar medium to 4 °C. Using this simple procedure, we successfully identified pectin-degrading microorganisms by observing colonies with halos on the clouded agar medium. We used alkaline pectinase and Bacillus halodurans, which is known to secrete alkaline pectinase, to establish the screening method. We demonstrated the screening of pectin-degrading microorganisms using the developed method and successfully isolated pectin-degrading microorganisms (Paenibacillus sp., Bacillus clausii, and Bacillus halodurans) from a soil sample. CONCLUSIONS: The developed method is useful for identifying pectin-degrading microorganisms.

A novel strategy of nanosized herbal Plectranthus amboinicus, Phyllanthus niruri and Euphorbia hirta treated TiO2 nanoparticles for antibacterial and anticancer activities.

Titanium dioxide nanoparticles exhibit good anticancer and antibacterial activities. They are known to be environmentally friendly, stable, less toxic, and have excellent biocompatibility nature. Due to these properties, they are well suited for biological applications particularly in biomedical applications such as drug delivery and cancer therapy. In this research article, three medicinal herbs namely, Plectranthus amboinicus (Karpooravalli), Phyllanthus niruri (Keezhanelli), and Euphorbia hirta (Amman Pacharisi), were used to modify the surface of the TiO2 nanoparticles. The synthesized nanoparticles were subjected to various characterization techniques. The samples are then subjected to MTT assay to determine cell viability. KB oral cancer cells are used for the determination of the anticancer nature of the pure and bio modified nanoparticles. It is observed that Plectranthus amboinicus-Phyllanthus niruri modified TiO2 nanoparticles exhibit excellent anticancer activities among other bio modified and pure samples. The samples are then examined for antibacterial activities against three Gram-negative bacterial strains namely, Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, and two Gram-positive bacterial strains namely, Staphylococcus aureus and Streptococcus mutans, respectively. Among the modified and pure samples, Plectranthus amboinicus showed good antibacterial activity against Gram-positive and Gram-negative bacteria. In the Flow cytometry analysis, the generation of p53 protein expression from Plectranthus amboinicus-Phyllanthus niruri modified TiO2 nano herbal particles shows the anti-cancerous nature of the sample. Then to determine the toxic nature of the Plectranthus amboinicus-Phyllanthus niruri modified TiO2 nano herbal particles against normal cells, the NPs were subjected to MTT assay against normal L929 cells, and it was found to be safer and less toxic towards the normal cells.

Electrospun fibers based on botanical, seaweed, microbial, and animal sourced biomacromolecules and their multidimensional applications.

This review summarizes and broadly classifies all of the major sustainable natural carbohydrate bio-macromolecular manifestations in nature - from botanical (cellulose, starch, and pectin), seaweed (alginate, carrageenan, and agar), microbial (bacterial cellulose, dextran, and pullulan), and animal (hyaluronan, heparin, chitin, and chitosan) sources - that have been contrived into electrospun fibers. Furthermore, a relative study of these biomaterials for the fabrication of nanofibers by electrospinning and their characteristics viz. solution behavior, blending nature, as well as rheological and fiber attributes are discussed. The potential multidimensional applications of nanofibers (filtration, antimicrobial, biosensor, gas sensor, energy storage, catalytic, and tissue engineering) originating from these polysaccharides and their major impacts on the properties, functionalities, and uses of these electrospun fibers are compared and critically examined.

Fabrication of Carboxymethyl Cellulose/Agar-Based Functional Films Hybridized with Alizarin and Grapefruit Seed Extract.

Carboxymethyl cellulose/agar-based functional halochromic films were fabricated by adding alizarin and grapefruit seed extract (GSE). The fillers were evenly dispersed in the polymer matrix to form compatible composite films. The addition of alizarin has improved the film's mechanical strength (20%) and water resistance (40%) with potent antioxidant and excellent color indicating properties. In contrast, GSE has imparted strong antibacterial and antioxidant activities to the film. Also, the addition of alizarin and GSE slightly improved the water vapor barrier properties but did not affect the thermal stability of the film. The composite film also exhibited UV blocking properties with adequate transparency. The composite film showed an excellent pH-dependent color change with color reversibility and color stability and a volatile gas detection function. The film also showed potent antimicrobial activity against foodborne pathogenic bacteria, Escherichia coli and Listeria monocytogenes, and showed an intense antioxidant action.

Physicochemical and transport properties of biodegradable agar films impregnated with natural semiochemical based-on hydroalcoholic garlic extract.

Biodegradable films based on agar with glycerol (GLY) as a plasticizer were developed by incorporating hydroalcoholic garlic extract (HGE) on the film surface. The effect of GLY content (0, 15, or 30 wt%) and different concentrations of HGE (0, 0.5, 1, or 1.5 µg/mL) on the physicochemical and transport properties of the films was evaluated. The optical (color and transparency), mechanical (tensile test), transport (diffusion and water vapor transmission rate), thermal (thermogravimetric analysis) structural (infrared spectroscopy and X-ray diffraction), and morphological (scanning electron microscope) properties were analyzed. The impregnation of HGE increased the transparency values and decreased the luminosity, tensile strength, elastic modulus, and crystallinity of the agar films. The formulation of 30 wt% GLY with 1.5 µg/mL HGE, identified as 30 GLY [1.5], showed a similar thermal stability that of a neat agar film. The agar films with 30 wt% GLY showed the lowest diffusion coefficient and water vapor transmission rate, indicating that volatile compounds are slowly released. From the results the formulation 30 GLY [1.5] could be used as a film to transport and to release HGE which is supported by a biodegradable matrix and this system has a potential use as insect semiochemical for plague control.

Effect of Different Culture Media, Grain Sources and Alternate Substrates on the Mycelial Growth of Pleurotus eryngii and Pleurotus ostreatus.

BACKGROUND AND OBJECTIVE: Oyster mushroom Pleurotus is one of the most aromatic edible mushrooms. This study evaluated a few selected determinants for promoting mycelial growth and spawn production of P. eryngii and P. ostreatus such as culture media, grain sources and alternate substrates. MATERIALS AND METHODS: Seven different substrate formulations were evaluated, viz: TS1 (100% wheat straw-S), TS2 (100% cardboard-C), TS3 (100% spent coffee ground-SCG), TS4 (50% S+50% C), TS5 (50% S+50% SCG), TS6 (80% S+20% C) and TS7 (80% S+20% SCG). The efficiency of different culture media potato dextrose agar (PDA), yeast malt agar ( YMA) and malt extract agar (MEA) and selected grains (wheat, rye, barley and oat) was investigated. Each study was arranged in the complete randomized design with 4 replicates. RESULTS: PDA media was the most suitable for mycelial growth of P. eryngii while P. ostreatus had a better mycelial growth on YMA and MEA media. Barley and rye grains were the most favourable for the mycelium growth of P. eryngii while oat grains were the best source that enhanced both of mycelial extension and density levels of P. ostreatus. The supplement of wheat straw (S) with SCG substrate improved mycelial extension while the substrate containing 50% S+50% C was the most favourable for both of mycelial growth and primordia formation in P. eryngii and P. ostreatus. CONCLUSION: The results revealed the feasibility of using recyclable wastes of cardboards and spent coffee ground for Pleurotus mushrooms cultivation. This would alleviate accumulation of urban generated wastes thus protecting the environment.

Anti-aging Effect of Agar Oligosaccharide on Male Drosophila melanogaster and its Preliminary Mechanism.

Agar oligosaccharide (AOS) is a marine prebiotic with apparent anti-inflammatory, antioxidant and anti-tumor effects. During this study, different doses of AOS are added to a basal diet to evaluate its effects on the lifespan, motor vigor and reproduction of male Drosophila melanogaster. Additionally, the activities of Cu,Zn-superoxide dismutase (Cu,Zn-SOD) and catalase (CAT) and the malondialdehyde (MDA) content in male Drosophila are examined on the 10th, 25th and 40th days. The fly midguts are removed on the 10th and 40th days for analyses of the intestinal microbial community by 16S rDNA sequencing and the expression level of intestinal immunity genes by quantitative real-time PCR (RT-PCR). The results show that AOS significantly prolonged the average and maximum lifespan and increased the antioxidant capacity of male Drosophila. Additionally, AOS significantly regulated the structure of the intestinal flora of "old" flies (40 days) and upregulated the expression of immune deficiency (IMD) genes to improve the intestinal immunity, which could be beneficial for delaying aging in old flies. The above-described results provide a theoretical basis for the application of AOS, a type of marine oligosaccharide, as a nutritional supplement or immunomodulator.

Generating cellulose-agar composite hydrogels for uptake-release kinetic studies of selenate and selenomethionine.

Cellulose-agar (CAB) composite hydrogel beads were generated for the uptake-release kinetics studies of Se(VI) and selenomethionine (SeMt) from water medium. The objective of this work is to analyze the surface structure, gel properties, thermal stability and chemical functionalities responsible for the adsorption of Se(VI) and SeMt. We propose here a possible mechanism for the adsorptions. Adsorption isotherms are in good agreement with the Freundlich model, yielding a high adsorption capacity for the CAB composite. Maximum adsorption capacity of Se(VI) and SeMt were found to be 7.083 mg g-1 and 34.639 mg g-1 respectively. The mean free energy of adsorption (E*) value was found to be 0.0423 kJ mol-1 and 0.329 kJ mol-1 of Se(VI) and SeMt respectively. 1 M HCl and 0.1 M HCl were able to desorb Se(VI) and SeMt respectively from CAB. The adsorption of Se(VI) was significantly reduced if As(III), Cr(III) and Hg(II) were present as complementary ions in the medium. Similar studies with pristine cellulose beads (CB) yielded insignificant uptake properties.

Interaction of South Asian spices with conventional antibiotics: Implications for antimicrobial resistance for Mycobacterium abscessus and cystic fibrosis.

Background: Antimicrobial resistance (AMR) has rendered certain species of Mycobacterium difficult to treat clinically, particularly, the nontuberculous Mycobacterium, Mycobacterium abscessus. This bacterium is emerging in specific disease populations, including amongst cystic fibrosis (CF) patients, where AMR represent a true treatment dilemma. Therefore, any innovation with traditional antimicrobial compounds in spices, which increases the potency of existing conventional antibiotics should be investigated. Methods: M. abscessus isolates (n = 9 multidrug-resistant clinical isolates from CF patients + 1 Reference Strain) were examined for their direct susceptibility to 27 spices, as well as the interactive effect of this spice combination to their susceptibility to amikacin and linezolid antibiotic, with standard disk diffusion assay. Results: Five isolates of M. abscessus (5/10; 50%) failed to grow on the spice enriched medium, which included four clinical isolates and the National Culture Type Collection (NCTC) Reference Strain. Of the remaining five isolates which grew on the spice medium, no cultural phenotypic differences were observed, compared to unsupplemented controls. In the case of both amikacin and linezolid, the zone of inhibition increased with the inclusion of the spices. Initially, all isolates of M. abscessus were fully resistant to linezolid (mean zone of inhibition = 0 mm), and growth was to the edge of the antibiotic disk, whereas when in the presence of spices, large zones of inhibition were observed (mean zone of inhibition = 33.3 mm). With amikacin, the mean zone of inhibition increased from 23.2 mm to 32.0 mm, in the presence of spices. Conclusion: These data suggest that the spices were interacting synergistically with the antibiotics, thus making the antibiotic more potent against the bacteria tested. This study is significant as it demonstrates a positive interaction between spices and the conventional antimycobacterial antibiotics, amikacin, and linezolid. Given the burden of AMR to M. abscessus, particularly in a patient with chronic disease such as CF, any food-related innovation that can help maximize the potency of existing antimycobacterial antibiotics is to be encouraged and developed. The specific mechanism as to how spices increase the potency of such antibiotics with M. abscessus needs to be elucidated, as well as novel food (spice) delivery modalities developed, including novel medicinal foodstuffs or functional foods, that can harness this beneficial effect in vivo to medicine and society.

Characterization of food additive-potato starch complexes by FTIR and X-ray diffraction.

Fourier-transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) techniques were used to study the effect of four food additives, agar, alginate, lecithin and glycerol, at three different concentrations, 0.5, 1 and 1.5%, on the molecular structure of potato puree prepared from commercial potato powder. Vibrational spectra revealed that the amylose-amylopectin skeleton present in the raw potato starch was missing in the potato powder but could be fully recovered upon water addition when the potato puree was prepared. FTIR peaks corresponding to water were clearly present in the potato powder, indicating the important structural role of water molecules in the recovery of the initial molecular conformation. None of the studied puree samples presented a crystalline structure or strong internal order. A comparison of the FTIR and XRD results revealed that the additives exerted some effects, mainly on the long-range order of the starch structure via interacting with and changing -OH and hydrogen bond interactions.

Optimization of pectinase immobilization on grafted alginate-agar gel beads by 24 full factorial CCD and thermodynamic profiling for evaluating of operational covalent immobilization.

Pectinase produced by a honey derived from the fungus Aspergillus awamori KX943614 was covalently immobilized onto gel beads made of alginate and agar. Polyethyleneimine, glutaraldehyde, loading time and enzyme's units were optimized by 24 full factorial central composite design (CCD). The immobilization process increased the optimal working pH for the free pectinase from 5 to a broader range of pH4.5-5.5 and the optimum operational temperature from 55°C to a higher temperature, of 60°C, which is favored to reduce the enzyme's microbial contamination. The thermodynamics studies showed a thermal stability enhancement against high temperature for the immobilized formula. Moreover, an increase in half-lives and D-values was achieved. The thermodynamic studies proved that immobilization of pectinase made a remarkable increase in enthalpy and free energy because of enzyme stability enhancement. The reusability test revealed that 60% of pectinase's original activity was retained after 8 successive cycles. This gel formula may be convenient for immobilization of other industrial enzymes.

Toxicological evaluation of neoagarooligosaccharides prepared by enzymatic hydrolysis of agar.

Agar, a heterogeneous polymer of galactose, is the main component of the cell wall of marine red algae. It is well established as a safe, non-digestible carbohydrate in Oriental countries. Although neoagarooligosaccharides (NAOs) prepared by the hydrolysis of agar by ß-agarase have been reported to exert various biological activities, the safety of these compounds has not been reported to date. For safety evaluation, NAOs containing mainly neoagarotetraose and neoagarohexaose were prepared from agar by enzymatic hydrolysis using ß-agarase DagA from Streptomyces coelicolor. Genotoxicity tests such as the bacterial reverse mutation assay, eukaryotic chromosome aberration assay, and in vivo micronucleus assay all indicated that NAOs did not exert any mutational effects. The toxicity of NAOs in rat and beagle dog models was investigated by acute, 14-day, and 91-day repeated oral dose toxicity tests. The results showed that NAO intake of up to 5,000 mg/kg body weight resulted in no significant changes in body weight, food intake, water consumption, hematologic and blood biochemistry parameters, organ weight, or clinical symptoms. Collectively, a no-observed-adverse-effect level of 5,000 mg/kg body weight/day for both male and female rats was established for NAO. These findings support the safety of NAO for possible use in food supplements and pharmaceutical and cosmetic products.

Phosphate-Catalyzed Hydrogen Peroxide Formation from Agar, Gellan, and κ-Carrageenan and Recovery of Microbial Cultivability via Catalase and Pyruvate.

Previously, we reported that when agar is autoclaved with phosphate buffer, hydrogen peroxide (H2O2) is formed in the resulting medium (PT medium), and the colony count on the medium inoculated with environmental samples becomes much lower than that on a medium in which agar and phosphate are autoclaved separately (PS medium) (T. Tanaka et al., Appl Environ Microbiol 80:7659-7666, 2014, https://doi.org/10.1128/AEM.02741-14). However, the physicochemical mechanisms underlying this observation remain largely unknown. Here, we determined the factors affecting H2O2 formation in agar. The H2O2 formation was pH dependent: H2O2 was formed at high concentrations in an alkaline or neutral phosphate buffer but not in an acidic buffer. Ammonium ions enhanced H2O2 formation, implying the involvement of the Maillard reaction catalyzed by phosphate. We found that other gelling agents (e.g., gellan and κ-carrageenan) also produced H2O2 after being autoclaved with phosphate. We then examined the cultivability of microorganisms from a fresh-water sample to test whether catalase and pyruvate, known as H2O2 scavengers, are effective in yielding high colony counts. The colony count on PT medium was only 5.7% of that on PS medium. Catalase treatment effectively restored the colony count of PT medium (to 106% of that on PS medium). In contrast, pyruvate was not as effective as catalase: the colony count on sodium pyruvate-supplemented PT medium was 58% of that on PS medium. Given that both catalase and pyruvate can remove H2O2 from PT medium, these observations indicate that although H2O2 is the main cause of reduced colony count on PT medium, other unknown growth-inhibiting substances that cannot be removed by pyruvate (but can be by catalase) may also be involved.IMPORTANCE The majority of bacteria in natural environments are recalcitrant to laboratory culture techniques. Previously, we demonstrated that one reason for this is the formation of high H2O2 levels in media prepared by autoclaving agar and phosphate buffer together (PT medium). In this study, we investigated the factors affecting H2O2 formation from agar. H2O2 formation is pH dependent, and ammonium ions promote this phosphate-catalyzed H2O2 formation. Amendment of catalase or pyruvate, a well-known H2O2-scavenging agent, effectively eliminated H2O2 Yet results suggest that growth-inhibiting factor(s) that cannot be eliminated by pyruvate (but can be by catalase) are present in PT medium.

Intelligent pH indicator film composed of agar/potato starch and anthocyanin extracts from purple sweet potato.

A new colorimetric pH indicator film was developed using agar, potato starch, and natural dyes extracted from purple sweet potato, Ipomoea batatas. Both agar and potato starch are solid matrices used to immobilize natural dyes, anthocyanins. The ultraviolet-visible (UV-vis) spectrum of anthocyanin extract solutions and agar/potato starch films with anthocyanins showed color variations to different pH values (pH 2.0-10.0). Fourier transform infrared (FT-IR) and UV-vis region spectra showed compatibility between agar, starch, and anthocyanin extracts. Color variations of pH indicator films were measured by a colorimeter after immersion in different pH buffers. An application test was conducted for potential use as a meat spoilage sensor. The pH indicator films showed pH changes and spoilage point of pork samples, changing from red to green. Therefore, the developed pH indicator films could be used as a diagnostic tool for the detection of food spoilage.

Characteristics of thermoplastic sugar palm Starch/Agar blend: Thermal, tensile, and physical properties.

The aim of this work is to study the behavior of biodegradable sugar palm starch (SPS) based thermoplastic containing agar in the range of 10-40wt%. The thermoplastics were melt-mixed and then hot pressed at 140°C for 10min. SEM investigation showed good miscibility between SPS and agar. FT-IR analysis confirmed that SPS and agar were compatible and inter-molecular hydrogen bonds existed between them. Incorporation of agar increased the thermoplastic starch tensile properties (Young's modulus and tensile strength). The thermal stability and moisture uptake increased with increasing agar content. The present work shows that starch-based thermoplastics with 30wt% agar content have the highest tensile strength. Higher content of agar (40wt%) resulted to more rough cleavage fracture and slight decrease in the tensile strength. In conclusion, the addition of agar improved the thermal and tensile properties of thermoplastic SPS which widened the potential application of this eco-friendly material. The most promising applications for this eco-friendly material are short-life products such as packaging, container, tray, etc.

A novel method for imaging the pharmacological effects of antibiotic treatment on Clostridium difficile.

Clostridium difficile is a significant cause of nosocomial-acquired infection that results in severe diarrhea and can lead to mortality. Treatment options for C. difficile infection (CDI) are limited, however, new antibiotics are being developed. Current methods for determining efficacy of experimental antibiotics on C. difficile involve antibiotic killing rates and do not give insight into the drug's pharmacologic effects. Considering this, we hypothesized that by using scanning electron microscopy (SEM) in tandem to drug killing curves, we would be able to determine efficacy and visualize the phenotypic response to drug treatment. To test this hypothesis, supraMIC kill curves were conducted using vancomycin, metronidazole, fidaxomicin, and ridinilazole. Following collection, cells were either plated or imaged using a scanning electron microscope (SEM). Consistent with previous reports, we found that the tested antibiotics had significant bactericidal activity at supraMIC concentrations. By SEM imaging and using a semi-automatic pipeline for image analysis, we were able to determine that vancomycin and to a lesser extent fidaxomicin and ridinilazole significantly affected the cell wall, whereas metronidazole, fidaxomicin, and ridinilazole had significant effects on cell length suggesting a metabolic effect. While the phenotypic response to drug treatment has not been documented previously in this manner, the results observed are consistent with the drug's mechanism of action. These techniques demonstrate the versatility and reliability of imaging and measurements that could be applied to other experimental compounds. We believe the strategies laid out here are vital for characterizing new antibiotics in development for treating CDI.

Chemical characterization of fatty acids, alkanes, n-diols and alkyl esters produced by a mixed culture of Trichoderma koningii and Penicillium janthinellum grown aerobically on undecanoic acid, potatoe dextrose and their mixture.

Little is known about the mixed fungal synthesis of high-value aliphatics derived from the metabolism of simple and complex carbon substrates. Trichoderma koningii and Penicillium janthinellum were fed with undecanoic acid (UDA), potatoe dextrose broth (PDB), and their mixture. Pyrolysis Field Ionization Mass Spectrometry (Py-FIMS) together with (1)H and (13)C Nuclear Magnetic Resonance (NMR) characterized CHCl3 soluble aliphatics in the fungal cell culture. Data from NMR and Py-FIMS analysis were complementary to each other. On average, the mixed fungal species produced mostly fatty acids (28% of total ion intensity, TII) > alkanes (2% of TII) > n-diols (2% of TII) > and alkyl esters (0.8% of TII) when fed with UDA, PDB or UDA+PDB. The cell culture accumulated aliphatics extracellularly, although most of the identified compounds accumulated intracellularly. The mixed fungal culture produced high-value chemicals from the metabolic conversion of simple and complex carbon substrates.

An integrated hybrid microfluidic device for oviposition-based chemical screening of adult Drosophila melanogaster.

Chemical screening using Drosophila melanogaster (the fruit fly) is vital in drug discovery, agricultural, and toxicological applications. Oviposition (egg laying) on chemically-doped agar plates is an important read-out metric used to quantitatively assess the biological fitness and behavioral responses of Drosophila. Current oviposition-based chemical screening studies are inaccurate, labor-intensive, time-consuming, and inflexible due to the manual chemical doping of agar. In this paper, we have developed a novel hybrid agar-polydimethylsiloxane (PDMS) microfluidic device for single- and multi-concentration chemical dosing and on-chip oviposition screening of free-flying adult stage Drosophila. To achieve this, we have devised a novel technique to integrate agar with PDMS channels using ice as a sacrificial layer. Subsequently, we have conducted single-chemical toxicity and multiple choice chemical preference assays on adult Drosophila melanogaster using zinc and acetic acid at various concentrations. Our device has enabled us to 1) demonstrate that Drosophila is capable of sensing the concentration of different chemicals on a PDMS-agar microfluidic device, which plays significant roles in determining oviposition site selection and 2) investigate whether oviposition preference differs between single- and multi-concentration chemical environments. This device may be used to study fundamental and applied biological questions in Drosophila and other egg laying insects. It can also be extended in design to develop sophisticated and dynamic chemical dosing and high-throughput screening platforms in the future that are not easily achievable with the existing oviposition screening techniques.