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Background: Intelligent food packaging that can monitor food quality and safety is essential in modern commercial trade. Research on the fabrication of environmentally friendly colorimetric labels that can indicate the freshness of food through color changes are needed. Methods: In this study, paper-based colorimetric labels were prepared using filter paper dipped into a solution of Roselle flower extract, and their performance in monitoring shrimp spoilage was investigated. Results: The labels’ response to ammonia vapor shows a distinct color variation from red to greenish-grey, corresponding to a sharp increase in the total color difference (ΔE = 32). The labels are relatively stable during storage at 4°C for up to 20 days. In shrimp freshness monitoring, the color changes from red to purple, which corresponds to increasing levels of total volatile basic nitrogen (TVB-N), and can be observed easily with the naked eye. Conclusion: This suggests that our paper-based colorimetric labels impregnated with Roselle extract show superior performance in detecting shrimp spoilage.

Recently, molybdenum disulfide (MoS2), have been explored as photothermal materials for solar evaporation. However, the optimum phase for photothermal material, 1T-MoS2 or 2H-MoS2, is still debatable. In this work, we observed the morphological and structural properties of MoS2 prepared by a simple hydrothermal process at 200 °C in three different growth times (16, 20, and 24 hours) using Na2MoO4·2H2O (sodium molybdate) as a Mo precursor, and CS(NH2)2 (thiourea) as S precursor. MoS2 nanoflowers were successfully prepared with nanosheets petals and its diameter increased from 0.4 to 2.8 and 4.5 as the growth time increased from 16 to 20 and 24 hours. The increase in growth time also led to improve the Mo:S ratio from 1:8 to 1:5 and facilitate the phase transformation from 1T to 2H as indicated by the shifting of (002) diffraction peak from 9.25° to higher degrees (12.98°, and 14.12°).

Zinc oxide (ZnO) has attracted considerable attention because of its potential applications in optoelectronic devices. Many scientists have reported on the preparation of ZnO based photodetectors in metal-semiconductor-metal (MSM) structures where expensive noble metals are used as electrodes. Here, we propose the preparation of full metal-oxide photoconductors by using indium tin oxide (ITO) as the electrodes and ZnO thin films as sensing materials. ZnO thin films were prepared by employing a simple ultrasonic spray pyrolysis (USP) technique with a commercial ultrasonic nebulizer (1.7 MHz). In this work, we developed a high performance ZnO based photodetector on interdigitated ITO with a simple and low-cost USP method. The I-V characteristic shows that ZnO thin film works in a photoconductive mode and has better performance as a UV (325 nm) detector than other wavelengths (505, 625 and 810 nm). As a UV detector, the devices exhibit high sensitivity (1255.51%), high responsivity (22.6 x 103 A/W), high detectivity (1.49 x 1014 Jones), good stability, a fast response time of 0.87 s and a relatively slow recovery time of 34.8 s. This high performance may be related to the large crystallite size that facilitates higher electron mobility.

Silver nanoparticles are well known for their antimicrobial properties and have been widely used in medical and industrial applications to prevent the growth of microorganisms. The effectiveness of silver nanoparticles (AgNPs) as an antimicrobial material is influenced by their shape and size; the smaller the size, the more active the AgNPs. To prevent aggregation, the nanoparticles can be maintained by stabilizing agents. This study aims to synthesize silver nanoparticles in situ using cellulose paper and to evaluate their antimicrobial activity. For reduction of Ag+ ions were used propane-1,2-diol. The reduction was carried out at 60, 80, and 100o C to accelerate the reaction. The formation of silver nanoparticles can be seen from the change in paper color from white to yellow or brown. This result is confirmed by the occurrence of the absorption peak in the UV-Vis spectrum between 300-500 nm. The TEM image shows the size distribution of silver nanoparticles affected by their reduction temperature. Antimicrobial tests provide a clear zone from the bottom of the paper to the edge. The reaction temperature at 60o C showed the best antimicrobial activity with AgNPs averaging at 6 nm. This method can be applied to antimicrobial paper preparation with controlled size and distribution.

Ammonia is one of the compounds released during the food spoilage process, so a device that can detect ammonia can be used as an indicator of food spoilage. This article reports on the preparation and characteristics of Starch/PVA composite films with Syzygium oleana as indicator films to detect ammonia vapor. The indicator was made by first preparing the starch / PVA composite films by casting method and then the films were dipped in Syzygium oleana extract. These films were characterized by using a UV-Vis spectrophotometer, Fourier Transformed Infra-Red Spectrophotometer and tested for mechanical properties such as tensile strength and elongation, and the water vapor transmission rate (WVT). The results showed that the addition of PVA reduced the absorbance value in the UV and visible area, the value of the water vapor transmission rate and the tensile strength but the elongation value of the film on the other hand rose. The indicator films can detect ammonia which was marked by its color change from red to blue. For further application, it can be used as a smart packaging label that can detect food freshness.

The detection of chemical pollution in an ecosystem requires rapid and accurate analysis in the field. The method presented here can help minimize preparation time and simple detection of the metal ions. Silver nanoparticles are known for their surface plasmon resonance characteristics that visibly display distinctive colors; this makes it possible to develop as colorimetric indicators. In this study, silver nanoparticles were synthesized on paper using velvet apple (Diospyros discolor Willd.) leaf extract as the Ag+ reducing agent. The paper was immersed in the water extract for 1 hour and for 24 hours. The formation of silver nanoparticles was indicated by the change in the paper’s color from white to light brown and dark brown. Furthermore, the paper was tested using several types of metal ions, namely, Cu2+, Mn2+, Pb2+, Zn2+, Mg2+, Ni2+ and Co2+. For all types of metal ions, the paper’s color changed selectively while detecting Cu2+ ions. The paper-based silver nanoparticles were sensitive enough to detect Cu2+ ions starting at concentrations of 100 mg/L. The Transmission Electron Microscope (TEM) revealed that the silver nanoparticles tended to aggregate after the addition of Cu2+ ions, which caused changes in the size and LSPR of the nanoparticles. This potential method needs further refinement and development to enhance the sensitivity of the paper-based colorimetric indicator, so that it can detect Cu2+ at lower concentrations.

Colloidal metal and their alloys nanoparticles have been found to potentially offer exceptional catalytic activity. Many researchers have worked to tailor the shape, size, and atomic composition of Au-based bimetallic nanocrystals to enhance their catalytic activity. However, the study of free colloidal anisotropic Au-based particles as catalyst of hydrogenation process is still limited. Here, we evaluated the bimetallic gold-silver (AuAg) mesoflowers (MFs) with sharp tips as a catalyst for hydrogenation of acetone to isopropanol under microwave radiation. The shape and size of the branched MFs was adjusted by controlling the addition of AgNO3 precursor. The resulting AuAg MFs were found to have higher catalytic activity than monometallic Au mesoparticles (Au MPs). The degradation rate of acetone without a catalyst is ±46%, while the degradation rate of acetone in the presence of Au MPs and AuAg MFs catalysts is ±66%, and ±71%, respectively. These correspond to the turn over number (TON) and turn over frequency (TOF) values of approximately 1827 and 9.1 s−1, respectively, for the AuAg MFs. This is significantly higher compared to the TON and TOF values for Au MPs, i.e. 746 and 3.7 s−1, respectively. High electron density on their sharp tips and the presence of Ag atoms on the AuAg alloy surface may be the key points in enhancing the chemical reaction with the oxygen atom in the C═O bond and generates a surface-hydrogen species to form isopropanol molecules.

Recent years have witnessed the growing interest in Zinc oxide (ZnO) in nanoscale size on antimicrobial and nanomedicine applications. Two main antimicrobial mechanisms of ZnO, photo-catalysis, and Zn2+, ion release has left some possibilities for some improvement, including producing hybrid metal-ZnO nanoparticles and introducing dopant material into ZnO structure. Silver (Ag) is applied to the ZnO structure to improve the antimicrobial properties of ZnO by modifying the optical and structural properties of ZnO such that the photo-catalysis mechanism can work under normal ambient room light conditions. Ag+ ion release is expected to work in synergy with the photo-catalysis mechanism of ZnO. Pulsed laser ablation in liquid (PLAL) technique is a very promising technique to produce nanoparticles as an antibacterial agent which requires high purity and clean surface of the nanoparticle. In this work, PLAL has been performed in pure water as the solution to produce ZnO and ZnO-Ag nanoparticles, by varying Ag ablation time 1, 3, and 5 minutes expecting various concentrations of Ag in the sample. All samples were tested to inactivate Staphylococcus aureus (S. aureus) growth for 12 hours’ incubation time, which shows a very prominent result. The number of living bacteria was found to be 4.42 log CFU/mL after 12 hours in contact with pure ZnO nanoparticle and it reduced significantly down to 1.48, 1.00 and 2.83 log CFU/mL respectively after contact with ZnO-Ag nanoparticle sample by varying Ag ablation time of 1, 3 and 5 minutes.

Gold nanoparticles possess a unique optical property, in which the color of colloidal solution changes as the properties of nanoparticles or surrounding medium change. Study on the so-called localized surface plasmon resonance (LSPR) of triangular gold nanoparticles is eminent, due to the growing interest in applying gold nanotriangles as colorimetric sensors. In this work, the size effect on the LSPR of triangular gold nanoparticles was studied by means of boundary element method (BEM) simulation. The dielectric constant of medium was set to reflect that of water, while the incident light was supposedly polarized in x and y direction. The simulation results were then used to evaluate the size evolution of triangular gold nanoparticles during laser-induced synthesis. The experiment was carried out by subjecting Au3+ ion solution to femtosecond laser irradiation for 5 s, before leaving it to grow for 24 h. The ion solution also contained 0.025 µM polyvinylpyrrolidone (PVP). Hydrogen peroxide (H2O2) was added shortly after laser irradiation to ensure complete reduction of Au3+ ion. During the post-irradiation period, the extinction was monitored hourly using UV-vis spectrophotometer. The simulation study using BEM revealed an exponential correlation between aspect ratio and extinction peak wavelength of gold nanotriangles. Using quasistatic approach, the extinction peak wavelength was expected to be independent from the nanotriangle height. Accordingly, only aspect ratio of a nanotriangle could be determined if the extinction peak wavelength was known. The dominant size of triangular gold nanoparticles formed during laser-induced synthesis showed an evolution as the autocatalytic growth progressed. The final aspect ratio (24 h after laser irradiation) was estimated to be 14.05. This result suggested the potential use of BEM simulation in studying the growth or decay of anisotropic nanoparticles.

The development of radiochromic indicator labels has recently become a fascinating research topic. In this experiment, carmoisine was used as a dye for paper indicator labels. This label was prepared by immersing paper in the carmoisine dye solution which has pH 2.0, 7.4 and 9.0. The prepared label was tested using a Co-60 source for doses of 5 to 100 kGy. The label's color stability was observed for 45 days. The labels color became more faded with increasing doses. The optical density and gray values increased linearly with increasing doses. The label color showed good stability for 45-day shelf life.

A novel dye-based biosensor with Au nanoparticles (Au NPs) for formaldehyde detection was fabricated with a simple method. Au NPs were grown on a glass substrate and then coated with a polyacrylate membrane film containing chromoionophore I (ETH 5294) and the alcohol oxidase enzyme (AOX). The analytical principle of biosensors is based on the color change of dye chromoionophore due to photoexcitation of electrons upon the selective binding with H+ ions resulted from the enzymatic oxidation reaction of formaldehyde. The presence Au NPs has improved the performance of biosensors may be due to the enhanced scattering light around Au NPs in the vicinity of cromoionophore that was used to photoexcite more electrons of cromoionophore. The biosensor also displays good selectivity to formaldehyde when tested with acetaldehyde and methanol, reproducibility (RSD of 1.8%), and repeatability (RSD of 3.3%) and a lifetime of 21 days.

Photocatalytic degradation is developing rapidly due to its simple and low-cost process, which results in effective and complete mineralization with no waste disposal problems. In this work, we report the enhancement of Rhodamine 6G (R6G) photocatalytic degradation by applying silver (Ag) nanoparticles on a zinc oxide (ZnO) nanoparticle structure using a pulsed laser ablation in liquid (PLAL) technique. The unique structure was obtained without applying any chemical substance and the Ag concentration was varied by changing the Ag target ablation time from 1 to 5 min. Generally, the inclusion of Ag increased the photocatalytic ability of ZnO and facilitated a higher degradation rate of R6G than pure ZnO. The generation of hydroxyl radical ( OH • ) was found as the main oxidative pathway, which led to R6G degradation by cleaving the chromophore structure. The kinetics of the photocatalytic degradation reaction was also carried out in this work. This research showed the great potential of a hybrid nanomaterial, developed through a laser ablation technique, for environmental protections.

The development of new material properties for antimicrobial agents to address the problem of antibiotic resistance is currently being explored. Silver and copper exhibit oligodynamic properties, which inhibit the growth of microorganisms. These properties are stronger at the nanoscale than the macroscale, especially for bimetallic nanoparticles (NPs). In this study, we synthesized bimetallic CuO and Ag NPs using Diospyros discolor Willd. (Velvet apple) leaf extract with three different ratios of Cu and Ag precursors: 1:0.01, 1:0.1, and 1:1 (v/v). In addition, the optical properties of these NPs were characterised using UV-Vis spectrophotometer, which showed the typical absorbance peak in the range of 300–400 nm. The size and shape of the CuO and Ag nanoparticles were analysed using a scanning electron microscope (SEM) and transmission electron microscope (TEM) images. The SEM and TEM images showed leaf-shaped CuO nanoplates and spherical AgNPs. Furthermore, the crystalline properties were analysed using x-ray diffraction (XRD). This study produced CuO-Ag nanoclusters with a particular morphology, size, and composition. The antibacterial assay showed potential broad-spectrum activity for Gram-positive bacteria (Staphylococcus aureus and Bacillus subtilis) as well as Gram-negative bacteria (Escherichia coli and Pseudomonas aeruginosa).

Silver Nanoparticles (AgNPs) recently have received considerable attention due to their unique chemical and physical properties which affect their sizes and shapes. The need to optimize the synthesis of Silver nanoparticles (AgNPs) is essential to develop effective colorimetry censors. Herein, the effect of sodium chloride on the reduction process of silver nitrate (AgNO3) into the final product of AgNps had been investigated. AgNPs have been synthesized using sodium chloride and polyvinyl alcohol (MW: 60,000 Da) as a reducing agent and a capping agent, respectively. The particles were collected and examined using ultraviolet-spectroscopy, transmission electron microscopy, and x-ray diffraction. The result showed that the concentration of sodium chloride affects the reduction process of Ag+ into AgNPs. At 1% concentration of sodium chloride, AgNPs were formed in 7 hours. In contrast, by reducing the concentration of sodium chloride to 0% has resulted slower AgNPs formation in 24 hours. The high sodium chloride concentration leads to the formation of silver chloride, which been investigated using the x-ray diffraction analysis. Besides, the transmission electron microscopy analysis showed that two different-shaped AgNPs were formed from the reaction. Therefore, the formation of AgNP particles was increased through the formation of transition molecule, silver chloride, by adding a higher concentration of sodium chloride.

Silver nanoparticles (AgNPs) are a widely developed noble metal nanoparticle that possesses antimicrobial activity. The advantages of AgNPs is their nature and ability to inhibit microbial growth, making them a potential alternative material to overcome the problem of antibiotic resistance. The synthesis of AgNPs can be done through a biosynthesis process using plant extracts as a bio-reductant. The extract preparation can affect the synthesis process, including the reaction rate and AgNP size. In this study, AgNPs were obtained through the biosynthesis process using 3 different extract preparations from Diospyros discolor Willd. (Bisbul) as the reducing agent. The extract was prepared by different extraction methods, including water extract, crude water extract, and methanol-water extract fraction. The formation of AgNPs was confirmed using an ultraviolet-visible spectrophotometer. The dispersity and zeta potential from the nanoparticles was confirmed using Particle Size Analyzer (PSA). The results obtained showed that all of the extract preparations can produce AgNPs. Depending on their characteristics, different extract preparations tend to have different reaction speeds, sizes, and distributions of the AgNPs formed. The activities of AgNPs against Staphylococcus aureus and Escherichia coli were also tested. The result showed that all AgNPs synthesized using the extracts had good antimicrobial activity, but the crude water extract and methanol-water extract had the strongest activity. Based on their spectral features, these two extracts tend to produce small sized particles and monodispersed distribution.

Diospyros discolor Willd. (Bisbul) is known to have an activity as a reducing agent to reduce silver ions into silver nanoparticles. These abilities affected by the phytochemical content in the extract, such as phenolics and flavonoids compounds, which makes the synthesis process to be environmentally friendly. In this study, various concentrations of crude water extract from Bisbul leaves were used at concentration 0.01, 0.025, and 0.05 % (w/v), with the ratio between the extract and 1 mM AgNO3 was 1:9 (v/v). The formation of silver nanoparticles are confirmed by the presence of absorption spectra between 350-450 nm using UV-Vis spectrophotometer. Based on the results of phytochemical tests, it showed that the extract contains phenols and flavonoids compound. Furthermore, the total flavonoid content (TFC) and total phenolic content (TPC) were measured to know their presence in the extract. The amount of those compounds in each extract concentration tend to increase with the increasing of extract concentration. The extract with concentration 0.05 % had a narrower peak width based on the Full Width at Half Maximum (FWHM) value, which can indicate the monodispersity in silver nanoparticles size and distribution.

Biodegradable and non-toxic plastic as food packaging is used instead of conventional plastic. One of biodegradable and non-toxic plastic can be made from cassava starch and PVA. This paper reports the results of a study of the effect of glycerol content on the mechanical and water barrier properties of cassava starch/Polyvinyl alcohol (PVA) composite films. The composite films of cassava starch/PVA were prepared with a solution casting method by the addition of glycerol or not. Glycerol concentrations in composite films varied from 10, 20 and 30% by weight of the polymer in the mixture. Mechanical and water barrier properties of cassava starch/PVA were analyzed. Film transparency was analyzed using a UV-Vis spectrophotometer. Changes in the functional groups on the FTIR spectra of composite films were also observed. Tensile strength decreased with increasing glycerol concentration on composite films but increased the elongation. The addition of glycerol decreased the water barrier properties by increasing the rate of transmission of water vapor from cassava starch/PVA composite films. Film transparency increased with the addition of 10% and 20% glycerol then decreases when the addition of 30% glycerol. Mechanical and water barrier properties of the composite films indicated that the addition of glycerol modified their properties significantly.

Dried sea cucumber (Beche-de-mer), the product after cleaning, boiling, salting, and drying, is as delicious and healthy food. Dried sea cucumber (Beche-de-mer) also has a high market price and the highest nutritional value of all seafood products. Moisture content in dried sea cucumber (Beche-de-mer) can affect the international market prices of dried sea cucumber to decline. This condition takes place because the moisture content is one of the parameters that determine the quality of dried sea cucumber. Therefore, this research will discuss a prediction system for measuring moisture content in dried sea cucumber (Beche-de-mer) using hyperspectral imaging technique. This system uses reflectance mode with the wavelength from 400 to 1000 nm. The hardware from the prediction system for measuring moisture content is motors to generate, hyperspectral camera system, two 150 W halogen lamps, Teflon table, and personal computer link. Then, the PLSR algorithm is applied to the prediction system model at full wavelength. The prediction model is used to obtain the predicted value of moisture content. Then the results of the prediction model are compared with the data references obtained by the gravimetric method. The root means square errors and correlation coefficient are used to evaluate the prediction system performance of moisture content prediction. The best result of the prediction system in this work is to have a correlation coefficient of 0.99 and root mean square errors of 0.92% respectively, with the number of PLS component is 30. Based on the results of this research, the proposed system can be used as an alternative method of measuring the moisture content in dried sea cucumber (Beche-de-mer) with excellent accuracy and high reliability

ZnO is a promising candidate for ultraviolet (UV) detectors due to its wide bandgap, good transparency, non-toxicity, low cost, and simple preparation. However, the performance of ZnO is low because of its high recombination rate. One alternative solution is fabricating a heterostructure of ZnO with a transition metal dichalcogenide (TMD) compound. This study proposes the facile fabrication of ZnO nanorods decorated with MoSe2 nanosheets. MoSe2 nanosheets were synthesized using the liquid-phase exfoliation method and added to the surface of ZnO nanorods via spin coating. The photodetector performance was enhanced with the addition of MoSe2 nanosheets because the MoSe2 could trap the electrons of defect sites of ZnO; hence, it decreased the dark current and slightly increased the photocurrent. The responsivity increased from 1.03 to 1.25 A/W, the detectivity increased from 0.82 x 109 to 1.9 x 109 Jones, and the sensitivity increased from 1261% to 5701%.

Molybdenum disulfide (MoS2) generally has two main phases: semiconducting 2H-MoS2, with trigonal prismatic geometry, and metallic 1T-MoS2, with octahedral geometry. However, the 1T-MoS2 phase is metastable, and improvements are still needed in the synthesis process. In this study, we synthesized MoS2 using a simple hydrothermal method at either 180°C or 200°C for 24 h, using sodium molybdate dihydrate (Na2MoO4.2H2O) and thiourea (NH2CSNH2) as the Mo and S precursors. The study found that synthesis at 180°C produces flower-like MoS2 microspheres with an average diameter of 10 µm and a 1T phase, while MoS2 produced at 200°C has irregular lumps with a size range of 1–10 µm in a 2H phase with slightly higher (002) d-spacing (6.78Å).

Penelitian ini bertujuan untuk mengetahui komposisi kimia dan aktifitas antibakteri dari 6 jenis minyak atsiri Indoensia. Minyak atsiri tersebut adalah minyak ketumbar, minyak bunga cengkeh, minyak sereh dapur, minyak kulit jeruk purut, minyak kayu manis, dan minyak kapulaga. Penelitian dilakukan dalam dua tahap yaitu karakterisasi minyak atsiri menggunakan Gas Chromatography Mass Spectrometer (GC-MS) dan penentuan aktivitas antibakteri dari masing-masing minyak atsiri dengan bakteri gram positif Staphylococcus aureus NBRC 100910 dan bakteri gram negatif Escherichia coli NBRC 3301. Aktivitas antibakteri dinyatakan sebagai diameter zona hambat yang terbentuk pada saat pengujian. Minyak ketumbar, minyak sereh dapur dan minyak kayu manis memiliki aktivitas antibakteri yang kuat terhadap E. coli NBRC 330 dan S.aureus NBRC 100910 dengan diameter zona hambat pada E. coli NBRC 330 masing-masing sebesar 24 mm, 47 mm dan 34 mm; dan pada S.aureus NBRC 100910 masing masing sebesar 22 mm, 25 mm dan 35 mm. Minyak bunga cengkeh memiliki aktivitas antibakteri dengan tingkat sedang pada E. coli NBRC 330 (19 mm) dan kuat pada S.aureus NBRC 100910 (28 cm). Minyak kapulaga menunjukkan aktivitas antibakteri dengan tingkat sedang terhadap dua bakeri tersebut dengan diameter zona hambat 14 mm untuk E. coli NBRC 330 dan 12 mm untuk S.aureus NBRC 100910. Minyak kulit jeruk purut hanya memiliki aktivitas antibakteri terhadap S.aureus NBRC 100910 dengan diameter zona hambat sebesar 22 mm. Minyak ketumbar, minyak sereh dapur, dan minyak kayu manis berpotensi besar untuk diaplikasikan dalam memperpanjang umur simpan makanan melalui teknologi kemasan aktif berdasarkan aktivitas antibakterinya.

Peppermint oil was one of the essential oils with an antibacterial bioactive component and the potential to be used as an antibacterial label. The purposes of this research were preparing the antibacterial label and evaluate their activity in prolonging the storage of shrimp. Antibacterial label was created by loading the peppermint oil onto the recycled paper as a matrix. Peppermint oil was characterized with Gas Chromatography-Mass Spectrometry (GC-MS) to identified suspected antibacterial activity compounds. The results showed that peppermint oil contains 39.79% of menthol and 35.69% of menthone as the main component. Peppermint oil and antibacterial labels have been screened for Gram-positive bacteria Staphylococcus aureus NBRC 100910 and Gram-negative bacteria Escherichia coli NBRC 100910 using the paper disk diffusion method. Peppermint oil has antibacterial activity in both bacteria, and the label only have antibacterial activity in E. coli NBRC 100910. The antibacterial labels research on prolonging the storage of shrimp shown that the Total Volatile Basic Nitrogen (TVBN) value was lower than without using the label. The results on this study showed recycled paper filled with peppermint oil can be used as an antibacterial label for an active packaging system.

Two-dimensional transition metal dichalcogenides such as molybdenum disulfide (MoS2) have attracted great attention due to their unique optical, electrical and chemical properties. MoS2 quantum dots (QDs) exhibit strong quantum confinement, high surface area and notable active edge sites compared to their bulk. In this work, MoS2 QDs were attached on the surface of ZnO nanorods (NRs) grown on interdigitated ITO substrates and then used as photodetector. MoS2 QDs were synthesized by a new ultrafast way pulsed laser ablation (PLA) in liquid method and then spincoated on the surface of ZnO NRs. The pristine ZnO and ZnO/MoS2 QDs photodetector were investigated under UV and visible light (325 nm, 505 nm and 635 nm) with the bias voltage -5 V to 5 V. The results show that the decoration of ZnO NRs by MoS2 QDs could enhance the sensitivity, responsivity and detectivity under UV irradiation. This may due to the decrease of dark current as the result of passivation of surface defects of ZnO NRs by MoS2 QDs.

This paper reports the results of a study relating to the synthesis of a novel ternary CoFe 2 O 4 /CuO/CoFe 2 O 4 thin film as a giant magnetoresistance (GMR) sensor. The CoFe 2 O 4 /CuO/CoFe 2 O 4 thin film was prepared onto silicon substrate via DC magnetron sputtering with the targets facing each other. X-ray diffraction was used to determine the structure of the thin film and a 4-point method was used to measure the MR ratio. The GMR ratio is highly dependent on the ferrimagnetic (CoFe 2 O 4 ) and nonmagnetic (CuO) layer thickness. The maximum GMR ratio at room temperature obtained in the CoFe 2 O 4 /CuO/CoFe 2 O 4 thin film was 70% when the CoFe 2 O 4 and the CuO layer had a thickness of 62.5 nm and 14.4 nm respectively.

Gamma radiation have dangerous effects and cannot be detected by the human body. Therefore, a detector that can detect the presence of a radiation source is needed, known as a radiation detector. Detector is a material that is sensitive to radiation. This study aims to make a gamma radiation dose detector using the principle of localized surface plasmon resonance (LSPR) silver nanoparticles and characterize it using a UV-Vis spectrophotometer. AgNO 3 solution was mixed with cobalt-60 radiation source Gammacell irradiator with small dose variations. PVA in this study acts as a capping for the formation of silver nanoparticles when irradiated. When the AgNO 3 solution mixed with PVA was irradiated with doses of 1Gy, 4Gy, 7Gy, 10Gy, 30Gy, 50Gy, 70Gy, 100Gy, 200Gy, 500Gy, and 1000Gy so that the color change from clear to yellowish with increasing doses, and the color change indicates that silver nanoparticles have been formed. The change in color from clear to yellowish is due to the occurrence of localized surface plasmon resonance (LSPR). The results of characterization of silver nanoparticles using a UV-Vis spectrophotometer showed that the maximum absorption of silver nanoparticles was between 410-446 nm to 0.5 M while at 1 M it was between 411-437 nm.

Silver nanoparticles can be synthesized through gamma ray irradiation and provide a localized surface plasmon resonance (LSPR) effect in the visible light so that it can be used as a dosimeter with the colorimetric principle. This article reports experimental results of radiosynthesis of silver nanoparticles in the medium of Tragacanth gum irradiated with gamma rays. The source of gamma rays is Cobalt-60 with varying doses between 1 - 40 kGy. The gel of AgNO3-Tragacanth which was originally clear starts to turn yellow at an irradiation dose of 10 kGy and becomes darker yellow with increasing radiation dose. The absorbance spectrum of the gel was characterized by using UV-visible instruments and give a maximum absorbance value at a wavelength of 403 nm which is a characteristic of LSPR of the silver nanoparticles. This maximum absorbance value increases with increasing radiation dose. These results indicate that the Ag-Tragacanth gel can be used as a gamma ray dosimeter.

Pulsed laser ablation in liquid (PLAL) technique has been used to synthesize ZnO and ZnO-Mg nanoparticles by conducting laser ablation of zinc target in pure water and Mg(NO3)2 solution. The absorbance spectra show redshifted peaks of ZnO with Mg inclusion indicating the lowering of the band-gap energy down to 3.09 and 3.01 eV from 3.28 eV of the pure ZnO. The higher frequency visible emission peaks of ZnO-Mg in the photoluminescence spectra indicate more recombination due to the formation of Mg interstitial state. The XRD measurement shows the diffraction of ZnO-Mg shifted into lower peak, resulting longer interplanar spacing, which matches to those obtained from HRTEM measurement.

Zinc oxide (ZnO) is a promising candidate for humidity-sensing materials due to its low-cost preparation, superior chemical and thermal stability, controllable surface morphology, and low water solubility. However, pristine ZnO-based humidity sensors suffer from poor response and large hysteresis that limit their application. In this study, n-type semiconducting tungsten disulfide (WS2) was utilized to form ZnO nanorods/WS2 nanosheets heterostructure grown on indium tin oxide coplanar electrode-coated glass substrate. The capacitive-type humidity sensing characteristics were investigated at room temperature. The results show that for humidity ranges of 18–85 % RH, three deposition cycles of WS2 nanosheets onto ZnO nanorods produced significant improvements in the response, sensitivity, and hysteresis with an unchanged response and recovery times compared to pristine ZnO sensors. This improved sensor performance might be due to the ability of WS2 to provide more water molecule adsorption sites. The formation of an n-n junction between ZnO and WS2 created interfaces with high local charge density and built an internal electric field that increase the water dissociation rate. The improved hysteresis might be due to water molecule adsorption on WS2 nanosheets is physical adsorption that facilitates the desorption process.

ZnO nanoparticles (NPs) have synthesized by sol-gel with different calcination temperatures. Scanning electron microscopy (SEM) shows that the morphology of ZnO NPs has large aggregation. Then, X-ray diffraction (XRD) technique confirmed that the XRD pattern of ZnO NPs has polycrystalline wurtzite structure. The crystallite size in (002) plane at a calcination temperature of 200 °C, 400 °C, 600 °C are 9.28 nm, 12.60 nm, 20.11 nm, respectively. The intensity of observed peaks increases when the calcination temperature is higher. The room temperature UV-Vis absorbance of ZnO NPs indicate that the higher calcination temperature cause absorption peak shifted to longer wavelength and the bandgap energy lower. Optical photoluminescence properties confirmed that the UV emission coincides with the green emissions which correspond to the electron transition from the bottom conduction band to Vo, Vzn, and Ozn level. As a result, all the samples of the ZnO NPs have single broad emission in the range of 330 nm-550 nm with the peak at the UV wavelength of 375 nm. Nevertheless, the PL pattern is not linearly with increasing calcination temperature.

Iron ions (Fe3+) is one of the most hazardous metals found in the water supply. The contamination of that metal originated from the corrosion process of pipes and cracks from waste disposal sites. High levels of iron would affect a bad impact to the environment. The current study aimed to synthesize silver nanoparticles (AgNPs) for heavy metals detection using a method which depends on colorimetric and optical changes. The approach to synthesize AgNPs adapted from polyol reduction method, i.e. by mixing polyvinyl alcohol (PVA), sodium chloride (NaCl) and silver nitrate (AgNO3). The colorimetric response of AgNPs to Fe3+ ions was observed visually and measured quantitatively by a spectroscopic method using a UV-Vis spectrophotometer. This work shows that the colloidal AgNPs were sensitive to identify Fe3+ ions.

pH is an important unit to represent the chemical condition of a liquid, solid substance, food nutrition, and microbial activity as well. pH value is also commonly used to detect the behaviour of chemical substances. Measurement of pH value can be shown by color changes of the substance based on the acidity condition from the measured environment. In this research, the colorimetric based on machine learning and pH value detected from the color information for point-of-care applications. For this investigation, we used the pH buffer solution and natural dyes derived from Brassica oleraceae (Red Cabbage) that shows colorimetric response gradually shifted from red to green along with the increasing of pH from 2.00 (acid) to 11.00 (alkaline). In this paper, we propose a method for predicting pH value based on Artificial Neural Network Regression (ANNR) and K-Nearest Neighbour Regression (KNNR) with RGB, HSV and LAB color space. As a result, the performance (99.83% ± 0.11) of this method could estimate the pH reasonably well for point-of-care application.

A simple colorimeter has been successfully designed using a microcontroller to detect food dyes. This article describes the performance specifications and design specifications of the colorimeter that was designed as a detector for food dyes using a photodiode sensor and a light emitting diode lamp as a source. System performance specifications consist of mechanical systems that are supported by electronic systems. Data collection techniques were carried out directly and indirectly. Color absorption data were measured directly using an ultraviolet-visible spectrophotometer and indirect absorption data is determined by the voltage that was processed by the microcontroller. The test was carried out by measuring 10 variations in the concentration of food dye liquid, in the range of 0.1% - 1.0%. Measurements were made with 10 repetitions. The data were analyzed in two ways, statistically and graphically. The accuracy of the colorimeter design was done by comparing it with the measurement results from the ultraviolet-visible spectrophotometer. The average percentage of errors are 1.7% and the average relative accuracy of the system is 93.3%. These results indicate that a simple colorimeter can be used to measure the concentration of food dyes quickly and with good accuracy.

Paper and plant extracts are materials that are cheap and easy to find everywhere, have great potential to be used as a portable, low-cost and biodegradable label for the application of chemical compounds detection. In this paper, we have explored potential methods for the label to detect ammonia gas, an indicator of meat spoilage, with the colorimetric principle. By immersing paper with plant extracts that are sensitive to ammonia, in this case, is anthocyanin from Ruellia simplex flower extract, the detection of ammonia at various concentrations can be achieved. Ammonia concentration used is 0; 0.005%; 0.025%; 0.1%, 0.25% and 0.5%. Color change images on the label when detection is scanned by a flatbed scanner. ImageJ software is used to quantify the color changes. Ammonia detection at various concentrations results in a color change from red to yellow on the paper label. Paper-based labels with discoloration that can be captured visually by the consumer’s eyes are considered as promising approaches to determine the freshness of meat.