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In this work, a refractive index sensor using TiO2 extracted from moringa leaves-based nanocomposite thin film was developed to detect cadmium ions in an aqueous solution. The experimental results showed a good sensitivity response of 0.4825° ppm−1, a strong binding affinity of 1.4362 ppm−1, and a low signal-to-noise ratio of 0.0755. The proposed sensor also showed good selectivity towards cadmium ions compared to zinc and mercury ions. The changes in the optical properties of titanium dioxide-based nanocomposite thin film towards different concentrations of cadmium ions solution were further demonstrated theoretically. Also, the observed increase in the surface roughness using atomic force microscopy proved the binding of Cd ions to the sensor film. This study is proposing a new potential of titanium dioxide extracted from moringa leaves-based nanocomposite thin film as a surface refractive index sensor for the detection of cadmium ions.

In the present work, graphene oxide (GO)–polyvinyl alcohol (PVA) composites thin film has been successfully synthesized and prepared by spin coating techniques. Then, the properties and morphology of the samples were characterized using Fourier transform infrared spectroscopy (FTIR), ultraviolet-visible spectroscopy (UV-Vis), and atomic force microscopy (AFM). Experimental FTIR results for GO–PVA thin film demonstrated the existence of important functional groups such as -CH2 stretching, C=O stretching, and O–H stretching. Furthermore, UV-Vis analysis indicated that the GO–PVA thin film had the highest absorbance that can be observed at wavelengths ranging from 200 to 500 nm with a band gap of 4.082 eV. The surface morphology of the GO–PVA thin film indicated the thickness increased when in contact with carbaryl. The incorporation of the GO–PVA thin film with an optical method based on the surface plasmon resonance (SPR) phenomenon demonstrated a positive response for the detection of carbaryl pesticide as low as 0.02 ppb. This study has successfully proposed that the GO–PVA thin film has high potential as a polymer nanomaterial-based SPR sensor for pesticide detection.

Arecanut husk (AH) was selected as a material for silica replacement in the synthesis process of glass-ceramics zinc silicate and also the fact that it has no traditional use and often being dumped and results in environmental issues. The process of pyrolysis was carried out at temperature 700 °C and above based on thermogravimetric analysis to produce arecanut husk ash (AHA). The average purity of the silica content in AHA ranged from 29.17% to 45.43%. Furthermore, zinc oxide was introduced to AHA and zinc silicate started to form at sintering temperature 700 °C and showed increased diffraction intensity upon higher sintering temperature of 600 °C to 1000 °C based on X-ray diffraction (XRD) analysis. The grain sizes of the zinc silicate increased from 1011 nm to 3518 nm based on the morphological studies carried out by field emission scanning electron microscopy (FESEM). In addition, the optical band gap of the sample was measured to be in the range from 2.410 eV to 2.697 eV after sintering temperature. From the data, it is believed that a cleaner production of low-cost zinc silicate can be achieved by using arecanut husk and have the potential to be used as phosphors materials.

A novel vanadium–cellulose composite thin film-based on angular interrogation surface plasmon resonance (SPR) sensor for ppb-level detection of Ni(II) ion was developed. Experimental results show that the sensor has a linear response to the Ni(II) ion concentrations in the range of 2–50 ppb with a determination coefficient (R2) of 0.9910. This SPR sensor can attain a maximum sensitivity (0.068° ppb−1), binding affinity constant (1.819 × 106 M−1), detection accuracy (0.3034 degree−1), and signal-to-noise-ratio (0.0276) for Ni(II) ion detection. The optical properties of thin-film targeting Ni(II) ions in different concentrations were obtained by fitting the SPR reflectance curves using the WinSpall program. All in all, the proposed Au/MPA/V–CNCs–CTA thin-film-based surface plasmon resonance sensor exhibits better sensing performance than the previous film-based sensor and demonstrates a wide and promising technology candidate for environmental monitoring applications in the future.

In this paper, the structural and optical properties of ZnO-SiO2-based ceramics fabricated from oil palm empty fruit bunch (OPEFB) were investigated. The OPEFB waste was burned at 600, 700 and 800 °C to form palm ash and was then treated with sulfuric acid to extract silica from the ash. X-ray fluorescence (XRF) and X-ray diffraction (XRD) analyses confirmed the existence of SiO2 in the sample. Field emission scanning electron microscopy (FESEM) showed that the particles displayed an irregular shape and became finer after leaching. Then, the solid-state method was used to produce the ZnO-SiO2 composite and the samples were sintered at 600, 800, 1000, 1200 and 1400 °C. The XRD peaks of the Zn2SiO4 showed high intensity, which indicated high crystallinity of the composite. FESEM images proved that the grain boundaries were larger as the temperature increased. Upon obtaining the absorbance spectrum from ultraviolet–visible (UV–Vis) spectroscopy, the energy band gaps obtained were 3.192, 3.202 and 3.214 eV at room temperature, 600 and 800 °C, respectively, and decreased to 3.127, 2.854 and 2.609 eV at 1000, 1200 and 1400 °C, respectively. OPEFB shows high potential as a silica source in producing promising optical materials.

It has been known for years that the phenolic compounds are able to exert harmful effects toward living organisms including humans due to their high toxicity. Living organisms were exposed to these phenolic compounds as they were released into the environment as waste products from several fast-growing industries. In this regard, tremendous efforts have been made by researchers to develop sensing methods for the detection of these phenolic compounds. Graphene and conducting polymers-based materials have arisen as a high potential sensing layer to improve the performance of the developed sensors. Henceforth, this paper reviews the existing investigations on graphene and conducting polymer-based materials incorporated with various sensors that aimed to detect hazardous phenolic compounds, i.e., phenol, 2-chlorophenol, 2,4-dichlorophenol, 2,4,6-trichlorophenol, pentachlorophenol, 2-nitrophenol, 4-nitrophenol, 2,4-dinitrophenol, and 2,4 dimethylphenol. The whole picture and up-to-date information on the graphene and conducting polymers-based sensors are arranged in systematic chronological order to provide a clearer insight in this research area. The future perspectives of this study are also included, and the development of sensing methods for hazardous phenolic compounds using graphene and conducting polymers-based materials is expected to grow more in the future.

There are extensive studies on the development of composite solutions involving various types of materials. Therefore, this works aims to incorporate two polymers of nanocrystalline cellulose (NCC) and poly(3,4-ethylenethiophene) (PEDOT) to develop a composite thin film via the spin-coating method. Then, Fourier transform infrared (FTIR) spectroscopy is employed to confirm the functional groups of the NCC/PEDOT thin film. The atomic force microscopy (AFM) results revealed a relatively homogeneous surface with the roughness of the NCC/PEDOT thin film being slightly higher compared with individual thin films. Meanwhile, the ultraviolet/visible (UV/vis) spectrometer evaluated the optical properties of synthesized thin films, where the absorbance peaks can be observed around a wavelength of 220 to 700 nm. An optical band gap of 4.082 eV was obtained for the composite thin film, which is slightly lower as compared with a single material thin film. The NCC/PEDOT thin film was also incorporated into a plasmonic sensor based on the surface plasmon resonance principle to evaluate the potential for sensing mercury ions in an aqueous medium. Resultantly, the NCC/PEDOT thin film shows a positive response in detecting the various concentrations of mercury ions. In conclusion, this work has successfully developed a new sensing layer in fabricating an effective and potential heavy metal ions sensor.

Dengue viral infection is one of the most common deadliest diseases and has become a recurrent issue for public health in tropical countries. Although the spectrum of clinical diagnosis and treatment have recently been established, the efficient and rapid detection of dengue virus (DENV) during viremia and the early febrile phase is still a great challenge. In this study, a dithiobis (succinimidyl undecanoate, DSU)/amine-functionalized reduced graphene oxide-–polyamidoamine dendrimer (DSU/amine-functionalized rGO–PAMAM) thin film-based surface plasmon resonance (SPR) sensor was developed for the detection of DENV 2 E-proteins. Different concentrations of DENV 2 E-proteins were successfully tested by the developed SPR sensor-based system. The performance of the developed sensor showed increased shift in the SPR angle, narrow full-width–half-maximum of the SPR curve, high detection accuracy, excellent figure of merit and signal-to-noise ratio, good sensitivity values in the range of 0.08–0.5 pM (S = 0.2576°/pM, R2 = 0.92), and a high equilibrium association constant (KA) of 7.6452 TM−1. The developed sensor also showed a sensitive and selective response towards DENV 2 E-proteins compared to DENV 1 E-proteins and ZIKV (Zika virus) E-proteins. Overall, it was concluded that the Au/DSU/amine-functionalized rGO–PAMAM thin film-based SPR sensor has potential to serve as a rapid clinical diagnostic tool for DENV infection.

Great efforts have been devoted to the invention of environmental sensors as the amount of water pollution has increased in recent decades. Chitosan, cellulose and nanocrystalline cellulose are examples of biopolymers that have been intensively studied due to their potential applications, particularly as sensors. Furthermore, the rapid use of conducting polymer materials as a sensing layer in environmental monitoring has also been developed. Thus, the incorporation of biopolymer and conducting polymer materials with various methods has shown promising potential with sensitively and selectively toward heavy metal ions. In this feature paper, selected recent and updated investigations are reviewed on biopolymer and conducting polymer-based materials in sensors aimed at the detection of heavy metal ions by optical methods. This review intends to provide sufficient evidence of the potential of polymer-based materials as sensing layers, and future outlooks are considered in developing surface plasmon resonance as an excellent and valid sensor for heavy metal ion detection.

In this study, the incorporation between gold modified-tyrosinase (Tyr) enzyme based graphene oxide (GO) thin film with surface plasmon resonance (SPR) technique has been developed for the detection of phenol. SPR signal for the thin film contacted with phenol solution was monitored using SPR technique. From the SPR curve, sensitivity, full width at half maximum (FWHM), detection accuracy (DA) and signal-to-noise ratio (SNR) have been analyzed. The sensor produces a linear response for phenol up to 100 µM with sensitivity of 0.00193° µM-1. Next, it can be observed that deionized water has the lowest FWHM, with a value of 1.87° and also the highest value of DA. Besides, the SNR of the SPR signal was proportional to the phenol concentrations. Furthermore, the surface morphology of the modified thin film after exposed with phenol solution observed using atomic force microscopy showed a lot of sharp peaks compared to the image before in contact with phenol proved the interaction between the thin film and phenol.

Dengue viral infection is one of the most common deadliest diseases and has become a recurrent issue for public health in tropical countries. Although the spectrum of clinical diagnosis and treatment have recently been established, the efficient and rapid detection of dengue virus (DENV) during viremia and the early febrile phase is still a great challenge. In this study, a dithiobis (succinimidyl undecanoate, DSU)/amine-functionalized reduced graphene oxide-–polyamidoamine dendrimer (DSU/amine-functionalized rGO–PAMAM) thin film-based surface plasmon resonance (SPR) sensor was developed for the detection of DENV 2 E-proteins. Different concentrations of DENV 2 E-proteins were successfully tested by the developed SPR sensor-based system. The performance of the developed sensor showed increased shift in the SPR angle, narrow full-width–half-maximum of the SPR curve, high detection accuracy, excellent figure of merit and signal-to-noise ratio, good sensitivity values in the range of 0.08–0.5 pM (S = 0.2576°/pM, R2 = 0.92), and a high equilibrium association constant (KA) of 7.6452 TM−1. The developed sensor also showed a sensitive and selective response towards DENV 2 E-proteins compared to DENV 1 E-proteins and ZIKV (Zika virus) E-proteins. Overall, it was concluded that the Au/DSU/amine-functionalized rGO–PAMAM thin film-based SPR sensor has potential to serve as a rapid clinical diagnostic tool for DENV infection.

In this research, influence of zinc oxide (ZnO) addition in silica matrix to produce zinc silicate glass system (ZnO–SiO2) derived from white rice husk ash (WRHA) have been investigated via solid state method. The 90 wt percentage (wt.%) of silica content in WRHA has been proved by X-ray fluorescence spectroscopy (XRF). Hence, the compositions of (ZnOx–WRHA1-x) glass system were varied by x = 0.50, 0.55, 0.60, 0.65 and 0.70 wt% to study their structural and optical behaviors. The X-ray diffraction (XRD) patterns revealed that with the addition of ZnO in the silica matrix, the broad halo peaks became weaker and caused a few crystalline peaks to appear. Meanwhile, Fourier transform infrared spectroscopy (FTIR) revealed that absorption bands related to SiO4 unit group are weakened as amount of ZnO increased. This is due to the increase of non-bridging oxygen's (NBO's) formation in the glass structure which also affects the absorbance measurement by ultra violet visible spectroscopy (UV–Vis) to be shifted towards higher in wavelength as the composition of ZnO increases. Lattice distortion due to NBO's formation had decreased the band gap values from 4.28 eV to 3.95 eV. Overall, 60:40 ratio of ZnO against WRHA was selected as the best ratio to produce zinc silicate (Zn2SiO4) glass ceramics. Lastly, the characterization of europium (Eu3+) doped Zn2SiO4 glass ceramics with subject to sintering temperature also has been studied to prove that this material can be a great potential host matrix for red-emitting phosphor.

In this study, highly functional cationically modified nanocrystalline cellulose (NCC)/carboxyl-functionalized graphene quantum dots (CGQD) has been described. The surface of NCC was first modified with hexadecyltrimethylammonium bromide (CTA) before combining with CGQD. The CGQD, CTA-NCC and CTA-NCC/CGQD nanocomposites thin films were prepared using spin coating technique. The obtained nanocomposite thin films were then characterized by using the Fourier transform infrared spectroscopy (FTIR) which confirmed the existence of hydroxyl groups, carboxyl groups and alkyl groups in CTA-NCC/CGQD. The optical properties of the thin films were characterized using UV–Vis spectroscopy. The absorption of CTA-NCC/CGQD was high with an optical band gap of 4.127 eV. On the other hand, the CTA-NCC/CGQD nanocomposite thin film showed positive responses towards glucose solution of different concentration using an optical method based on surface pla.smon resonance phenomenon. This work suggests that the novel nanocomposite thin film has potential for a sensing application in glucose detection

In this paper, the ZnO–SiO2 was synthesized using ZnO nanopowders and SiO2 developed from coconut husk ash by using conventional solid state method. The ZnO–SiO2 crystal system was heat-treated and the properties was studied. The XRD results showed high intensity peaks due to its high crystallinity when sintered at high temperature. The morphological differences can also be observed through FESEM images as the heat-treated crystal system showed well-distinct boundaries. Meanwhile, the absorbance intensity decreased and shifted to the lower wavelength after heat-treated. The optical band gap value of the ZnO–SiO2 was 3.22 eV before treated and increased to 4.05 eV after heat treated. The presented results showed good properties of zinc silicate and it has a great potential as phosphors in optical application.

In this study, synthesis and characterization of chitosan/maghemite (Cs/Fe2O3) composites thin film has been described. Its properties were characterized using Fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM) and ultraviolet-visible spectroscopy (UV-Vis). FTIR confirmed the existence of Fe–O bond, C–N bond, C–C bond, C–O bond, O=C=O bond and O–H bond in Cs/Fe2O3 thin film. The surface morphology of the thin film indicated the relatively smooth and homogenous thin film, and also confirmed the interaction of Fe2O3 with the chitosan. Next, the UV-Vis result showed high absorbance value with an optical band gap of 4.013 eV. The incorporation of this Cs/Fe2O3 thin film with an optical-based method, i.e., surface plasmon resonance spectroscopy showed positive response where mercury ion (Hg2+) can be detected down to 0.01 ppm (49.9 nM). These results validate the potential of Cs/Fe2O3 thin film for optical sensing applications in Hg2+ detection.

The growing demand for early detection of dengue virus (DENV) has contributed to integrated thin films with surface plasmon resonance (SPR) technique, i.e. Au/Fe-NCCCTAB/ IgM, Au/CdSQDs-RGO/IgM, Au/CdSQDs-PAMAM/IgM, and Au/DSU/RGOPAMAM/ IgM. Their sensing performances such as sensitivity, binding affinity, fullwidth- half-maximum (FWHM), detection accuracy (DA), and figure-of-merit (FOM) were analysed. The first developed Au/Fe-NCC-CTAB/IgM sensor film yielded the sensitivity of 27.051 °/nM, binding affinity of 0.862 TM-1, and high performances of DA and FOM on detection of 0.001 nM of DENV E-proteins. For Au/CdSQDs-RGO/IgM sensor film, the detection performance showed the sensitivity and binding affinity values of 5.496 °/nM and 0.775 TM-1, respectively. The results also showed that the sensor film had the highest DA and FOM values when detecting 0.001 nM of DENV E-proteins. The third developed Au/CdSQDs-PAMAM/IgM sensor film showed the sensitivity of 7.577 °/nM, binding affinity of 2.696 TM-1, and high performances of DA and FOM on detection of 0.001 nM of DENV E-proteins. The final development of SPR sensor integrated Au/DSU/RGOPAMAM/ IgM sensor film resulted in the sensitivity of 10.939 °/nM, binding affinity of 9.783 TM-1, and high performances of DA and FOM on detection of 0.0001 nM of DENV E-proteins. Structural investigations using Raman spectroscopy, Ultraviolet-visible near infrared (UV-Vis-NIR) spectroscopy, and Atomic force microscopy (AFM) have confirmed the presence of the conjugate DENV E-proteins-antibodies-nanocomposite layer. Most importantly, by comparing the performances of the sensor films described above, the results found that the Au/DSU/RGO-PAMAM/IgM is a very effective sensor film because it has the lowest quantitation limit and strongest binding affinity. Despite its low sensitivity, the sensitivity of detection was further enhanced by optimizing the fabrication of Au/DSU/RGO-PAMAM/IgM sensor film. The excellent sensitivity and binding affi

Label-free measurements of small-molecule binding interactions are of high interest to researchers across multiple scientific disciplines. Label-free optical sensors based on surface plasmon resonance (SPR) have been widely used for detecting various targets including toxic heavy metals in solutions. In this research, an SPR optical sensor enhanced with a 4-(2-pyridylazo)-resorcinol (PAR)-based composite layer was employed for the detection of the cobalt ion (Co2+). A binding analysis study was conducted by monitoring the interaction between Co2+ and the sensing layer thin film. In our experiment, there were no changes in SPR angle for a gold layer in contact with Co2+ of different concentrations, whereas the enhanced SPR sensor produced a maximum SPR angle shift of 0.328°. From the relationship between the angle shift and the concentration of Co2+, the sensor had a sensitivity of 0.2375° ppm−1 for concentrations of less than 1 ppm, 0.0044° ppm−1 for concentrations of 1 to 10 ppm, and 0.00069° ppm−1 for concentrations from 10 to 100 ppm. Further analysis was also carried out by calculating the full width at half maximum (FWHM), detection accuracy (DA), and signal-to-noise ratio (SNR). In the binding analysis, the experimental results were fitted with Langmuir, Freundlich, and Sips isotherm equations. It was found that the Sips isotherm equation most closely fitted the experimental data with an R2 value of 0.96716 and a binding affinity of 1.649 ppm−1.

The plethora of optical techniques have been developed to detect the dengue virus, regrettably, the existing techniques are cumbersome and have limitations to provide early identification of the low-level of dengue virus. For this purpose, surface plasmon resonance (SPR) optical sensor was designed with a highly sensitive thin film based on hyperbranched polymer nanocomposites for conjugation of antibodies that specifically detect the dengue virus type II (DENV). In particular, we investigate the SPR sensing performance for gold/cadmium sulfide quantum dots-polyamidoamine/antibody (Au/CdS QDs-PAMAM/IgM) sensor film in terms of linear sensitivity, binding affinity, detection accuracy, full-width-half-maximum, selectivity, and spike and recovery test. The results show a strong affinity value, good sensitivity and selectivity, high accuracy, and excellent recovery value, obeying the ideal value based on conventional assay analysis. Additionally, this Au/CdS QDs-PAMAM/IgM based SPR sensor was successfully applied for the lowest detection of 1 pM of DENV E-proteins. To this end, a highly sensitive Au/CdS QDs-PAMAM/IgM sensor film was characterized using Raman spectroscopy, ultraviolet-visible (UV–Vis-NIR) spectroscopy, and atomic force microscopy (AFM) to confirm the binding of DENV.

The development of optical sensors for heavy metal ion detection has been rapidly growing; unfortunately, the current methods suffer limitations that led to the emergence of an outstanding technique called surface plasmon resonance (SPR) spectroscopy. In this paper, the performance of the SPR optical sensor in detecting ferric ions (Fe3+) was successfully enhanced by depositing novel cetyltrimethylammonium bromide modified hydroxylated graphene quantum dots (CTAB/HGQDs) onto a gold (Au) thin film using the spin coating technique. Upon exposure to Fe3+, the SPR responses of both CTAB/HGQDs thin film and bare Au thin film were compared and studied, emphasizing the sensitivity, binding affinity, full width at half maxima, signal-to-noise ratio, and data accuracy. The CTAB/HGQDs thin film achieved a high sensitivity value of 29.886° ppm−1 for Fe3+ up to 0.1 ppm. The strong binding affinity was confirmed using the Langmuir isotherm model calculation. To the end, the CTAB/HGQDs thin film was characterized using atomic force microscopy for morphological study, confirming its interaction with Fe3+.

In this work, waste coconut husk ash was used to prepare a ZnO-SiO2 composite. Solid-state technique was used to fabricate the composite due to its producibility, simple procedure as well as lower production cost. At high sintering temperatures ranging from 600 °C to 1000 °C, the X-ray diffraction (XRD) peaks of the Zn2SiO4 showed high intensity, which indicated high crystallinity. Furthermore, the formation of broad bands of ZnO4, Si-O-Si, and SiO4 were detected by Fourier transform infrared (FTIR) spectroscopy and the bands became narrower with the increment of sintering temperature. Besides, the morphological image from field emission scanning electron microscopy (FESEM) showed the formation of densely packed grains and smooth surface composite with the increase of sintering temperature. Upon obtaining the absorbance spectrum from Ultraviolet–Visible (UV–Vis) spectroscopy, the optical band gap was calculated to be 4.05 eV at 1000 °C. The correlation between the structural and optical properties of ZnO-SiO2 composite was discussed in detail.

In this work, sensitive detection of dengue virus type 2 E-proteins (DENV-2 E-proteins) was performed in the range of 0.08 pM to 0.5 pM. The successful DENV detection at very low concentration is a matter of concern for targeting the early detection after the onset of dengue symptoms. Here, we developed a SPR sensor based on self-assembled monolayer/reduced graphene oxide-polyamidoamine dendrimer (SAM/NH2rGO/PAMAM) thin film to detect DENV-2 E-proteins. Surface characterizations involving X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR) confirms the incorporation of NH2rGO-PAMAM nanoparticles in the prepared sensor films. The specificity, sensitivity, binding affinity, and selectivity of the SPR sensor were then evaluated. Results indicated that the variation of the sensing layer due to different spin speed, time incubation, and concentration provided a better interaction between the analyte and sensing layer. The linear dependence of the SPR sensor showed good linearity (R2 = 0.92) with the lowest detection of 0.08 pM DENV-2 E-proteins. By using the Langmuir model, the equilibrium association constant was obtained at very high value of 6.6844 TM−1 (R2 = 0.99). High selectivity of the SPR sensor towards DENV-2 E-proteins was achieved in the presence of other competitors.

In this work, zinc silicate glass system (ZnO-SiO2) doped with various europium ion (Eu3+) concentrations derived from white rice husk ash (WRHA) were synthesized using melt and quench method. All samples determined by X-ray diffractometer (XRD) showed amorphous phase structure. The surface micrographs detected by Field emission scanning electron microscopy (FESEM) showed Eu3+ addition had reduced the sample’s porosity. Fourier transform infrared (FTIR) revealed the presence of Eu3+ ions had weakened the absorption peaks of SiO4. Meanwhile, ultra-violet visible spectroscopy (UV–vis) showed the absorption edges were shifted towards higher wavelength with Eu3+ addition. Band gap values were increased from 2.97 eV to 4.23 eV when Eu3+ dopant increased but decreased back to 3.98 eV at highest concentration. Photoluminescence spectroscopy (PL) analysis showed intense red emission at 600 nm corresponding to 5D0 → 7F2 transition were enhanced by Eu3+ doping. Hence, their luminescent properties are useful for optical device such as white light emitting diodes.

An optical sensor for the dengue virus (DENV) E-protein based on cadmium sulfide quantum dots composited with amine functionalized graphene oxide (CdS-NH2GO) thin film was successfully developed. A specific monoclonal antibodies (IgM) were covalently attached to CdS-NH2GO via EDC/NHS coupling to sense targeted E-proteins. The SPR sensor exhibited an excellent detection limit (0.001 nM/1 pM) with sensitivity of 5.49° nM−1 for the detection of DENV E-protein. The binding affinity, as well as the performance of the Au/CdS-NH2GO/EDC-NHS/IgM film, was successfully obtained at 486.54 nM−1 in detecting DENV E-proteins. These results indicated that the Au/CdS-NH2GO/EDC-NHS/IgM film shows high potential sensitive and stronger binding towards DENV E-protein.

In this research, the preparation of chitosan and hydroxyl-functionalized graphene quantum dots (HGQDs) composite has been described. The spin coating technique was used to prepare the chitosan/hydroxyl-functionalized graphene quantum dots (Cs/HGQDs) thin film. The Cs/HGQDs thin film was then characterized using the Fourier transform infrared spectroscopy which confirmed the existence of amino groups, carboxylic acid groups, carboxyl groups and hydroxyl groups in Cs/HGQDs. UV–Vis absorption spectroscopy and photoluminescence (PL) were used to study the optical properties of the thin film. The absorption of Cs/HGQDs thin film was high with optical band gap of 3.797 eV. The intensity of PL spectra of the thin film was observed around wavelength of 420 nm. The incorporation of Cs/HGQDs thin film with surface plasmon resonance spectroscopy produced positive responses towards the Fe³⁺ ion solutions of different concentration and it was found that Cs/HGQDs thin film able to detect Fe³⁺ as low as 0.5 ppm with a sensitivity of 0.11396° ppm⁻¹. Subsequently, Cs/HGQDs layer have high potential as sensing layer to detect Fe³⁺ due to high affinity of Fe³⁺ ion towards the thin film with a value of binding affinity constant, K equals to 5.79 ppm⁻¹. Atomic force microscopy was used to observe the surface morphology of the thin film and the result indicates that the thin film is relatively smooth and homogenous which also confirmed the interaction of Fe³⁺ with the thin film. Thus, Cs/HGQDs thin film shows potential for the detection of Fe³⁺ in solution.

About 71% of the Earth’s surface is covered with water. Human beings, animals, and plants need water in order to survive. Therefore, it is one of the most important substances that exist on Earth. However, most of the water resources nowadays are insufficiently clean, since they are contaminated with toxic metal ions due to the improper disposal of pollutants into water through industrial and agricultural activities. These toxic metal ions need to be detected as fast as possible so that the situation will not become more critical and cause more harm in the future. Since then, numerous sensing methods have been proposed, including chemical and optical sensors that aim to detect these toxic metal ions. All of the researchers compete with each other to build sensors with the lowest limit of detection and high sensitivity and selectivity. Graphene quantum dots (GQDs) have emerged as a highly potential sensing material to incorporate with the developed sensors due to the advantages of GQDs. Several recent studies showed that GQDs, functionalized GQDs, and their composites were able to enhance the optical detection of metal ions. The aim of this paper is to review the existing, latest, and updated studies on optical sensing applications of GQDs-based materials toward toxic metal ions and future developments of an excellent GQDs-based SPR sensor as an alternative toxic metal ion sensor.

The emergence of unintentional poisoning and uncontrolled vector diseases have contributed to sensor technologies development, leading to the more effective detection of diseases. In this study, we present the combination of graphene-based material with surface plasmon resonance technique. Two different graphene-based material sensor chips were prepared for rapid and quantitative detection of dengue virus (DENV) and cobalt ion (Co2+) as an example of typical metal ions. As the fundamental concept of surface plasmon resonance (SPR) sensor that relies on the refractive index of the sensor chip surface, this research focused on the SPR signal when the DENV and Co2+ interact with the graphene-based material sensor chip. The results demonstrated that the proposed sensor-based graphene layer was able to detect DENV and Co2+ as low as 0.1 pM and 0.1 ppm respectively. Further details in the detection and quantification of analyte were also discussed in terms of sensitivity, affinity, and selectivity of the sensor.

Semiconductor nanoparticles, cadmium sulfide quantum dots composited with amine functionalized graphene oxide (CdS-NH2GO) were functionalized with specific monoclonal antibodies (IgM) based on surface plasmon resonance (SPR) optical sensor for the detection of dengue virus (DENV) E-protein. The SPR results suggested that DENV E-protein can be detected in the range 0.0001–10 nM with the binding affinity of 486.54 nM−1. The successful binding between antibodies and antigens in an immunoassay sensor was further confirmed by Raman, UV–vis spectroscopy and atomic force microscopy (AFM). The Raman studies showed the depletion of protein molecules in the region of 120–1000 cm−1, which gives an evidence for the binding of DENV E-proteins to the antibodies. From UV–vis spectra, the absorption band was red shifted upon binding of DENV E-protein. The AFM measurement further confirmed the interaction occurred between DENV E-protein and the Au/CdS-NH2GO/IgM sensor surface.

In this study, surface plasmon resonance based on Kretschmann configuration is employed as an alternative method to detect adulteration of pure honey. The adulterated honey was prepared by diluting three types of sugar adulterants (fructose, glucose and sucrose) into pure honey. The concentration of each adulterant is tested from 2% until 10% adulteration with 0% adulteration represents the reference for pure honey. All the resonance angles of adulterated honey demonstrated similar behavior by shifting to smaller angle than pure honey. The measured sensitivities are 0.1266°/%, 0.1065°/%, and 0.0988°/% for fructose, glucose and sucrose adulterants, respectively. The shift of resonance angle as a function of adulterants concentration in pure honey was plotted with linear regression greater than 0.95 for all samples. The outcome has disclosed a real-time, rapid and non-destructive sensor to be promoted as well-developed honey sensor.

In this research, surface plasmon resonance (SPR) spectroscopy was used for sensing copper ion by combining the SPR with nanocrystalline cellulose modified by hexadecyltrimethylammonium bromide and graphene oxide composite (CTA-NCC/GO) thin film. The binding of Cu2+ on CTA-NCC/GO thin film was monitored by using SPR spectroscopy. By using the obtained SPR curve, detection range, binding affinity, sensitivity, full width at half maximum (FWHM), data accuracy (DA), and signal-to-noise ratio (SNR) have been calculated. The results showed that the sensor detection range was 0.01 until 0.5 ppm, and that it reached a saturation value. Moreover, the resonance angle shift followed the Langmuir isotherm model with a binding affinity constant of 4.075 × 103 M−1. A high sensitivity of 3.271° ppm−1 also was obtained for low Cu2+ concentration ranged from 0.01 to 0.1 ppm. For the FWHM, the lowest value calculated was at 0.08 and 0.1 ppm, which is 3.35°. The DA of the SPR signal consecutively highest at 0.08 and 0.1 ppm. Besides that, the SNR of the SPR signal increases with the Cu2+ concentrations. The CTA-NCC/GO thin film morphological properties were also studied by using atomic force microscopy. The rms roughness values, which were obtained before and after in contact with Cu2+, were 3.51 nm and 2.46 nm, respectively.

Purpose: This paper aims to review the potential application of surface plasmon resonance (SPR) in diagnosis of dengue virus (DENV-2) E-protein and the development of SPR to become an alternative DENV sensor. Design/methodology/approach: In this review, the existing standard laboratory techniques to diagnosis of DENV are discussed, together with their drawbacks. To overcome these drawbacks, SPR has been aimed to be a valuable optical biosensor for identification of antibodies to the DENV antigen. The review also includes the future studies on three-dimensional poly(amidoamine) (PAMAM) dendrimer-surface-assembled monolayer (SAM)-Au multilayer thin films, which are envisaged to have high potential sensitive and selective detection ability toward target E-proteins. Findings: Application of SPR in diagnosis of DENV emerged over recent years. A wide range of immobilized biorecognition molecules have been developed to combine with SPR as an effective sensor. The detection limit, sensitivity and selectivity of SPR sensing in DENV have been enhanced from time to time, until the present. Originality/value: The main purpose of this review is to provide authors with up-to-date and useful information on sensing DENV using SPR and to introduce a novel three-dimensional PAMAM-SAM-Au multilayer thin films for future research on SPR sensing applications.

In this study, the preparation of hexadecyltrimethylammonium bromide modified nanocrystalline cellulose/graphene oxide composite (CTA-NCC/GO) solution under mild condition has been described. The CTA-NCC/GO thin film then was prepared by spin coating technique. Moreover, the CTA-NCC/GO thin film was characterized by Fourier transform infrared spectroscopy (FTIR) and atomic force microscopy (AFM) for the structural properties while the optical properties were characterized by ultraviolet-visible (UV–vis). FTIR confirmed the functional group that is contained in CTA-NCC/GO thin film and the surface morphology obtained from AFM results showed that the thin film is homogenous. The UV–vis analysis also showed that CTA-NCC/GO thin film has high absorption with optical band gap of 4.00 eV. Furthermore, the CTA-NCC/GO thin film has been studied to be incorporated with surface plasmon resonance spectroscopy (SPR) to detect copper ion. The SPR results showed that copper ion can be detected as low as 0.01 ppm using this thin film.

In this study, the combination of novel valinomycin doped chitosan-graphene oxide (C–GO–V) thin film and surface plasmon resonance (SPR) system for potassium ion (K⁺) detection has been developed. The novel C–GO–V thin film was deposited on the gold surface using spin coating technique. The system was used to monitor SPR signal for K⁺ in solution with and without C–GO–V thin film. The K⁺ can be detected by measuring the SPR signal when C–GO–V thin film is exposed to K⁺ in solution. The sensor produces a linear response for K⁺ ion up to 100 ppm with sensitivity and detection limit of 0.00948° ppm⁻ᴵ and 0.001 ppm, respectively. These results indicate that the C–GO–V film is high potential as a sensor element for K⁺ that has been proved by the SPR measurement.

In this work, cadmium sulfide quantum dots composited with polyamidoamine dendrimer (CdSQDs-PAMAM) thin film had been successfully developed for use in the detection of dengue virus (DENV) E-proteins. Studies involving XRD, EDX, UV–Vis-NIR, and AFM analyses proved the presence of CdSQDs and PAMAM nanoparticles. The mechanism of sensor surface functionalization was confirmed using FTIR spectra. The SPR responses showed a significant shift in resonance angle after exposure to different concentrations of DENV E-protein solution. From this observation, the Au/CdSQDs-PAMAM/IgM sensor film obtained a quantification limit of 0.0001 nM with the association constant of 2.53 × 103 M−1, which was better compared to the Au/IgM and Au/PAMAM/IgM sensor films. The matrix analysis was successfully performed using spiked bovine serum albumin obtaining excellent recovery values in the results. The enhancement of the SPR responses thus showing the high potential of CdSQDs-PAMAM thin film as dengue sensing material in SPR techniques for the future development of dengue diagnostic.

Application of surface plasmon resonance (SPR) optical sensor in the diagnosis of dengue virus (DENV) emerged over recent years. Immobilized monoclonal antibody (IgM) on gold/Fe-MPA-NCC-CTAB/EDC-NHS thin film was prepared using a spin coating technique. DENV E-protein can be detected by measuring the SPR signal when IgM immobilized gold/Fe-MPA-NCC-CTAB/EDC-NHS thin film is exposed to the DENV E-protein solution, by varying the concentration ranging from 0.0001 nM to 10 nM. A linear relationship between the shift of SPR angle and concentration of DENV E-protein up to 0.01 nM, with sensitivity of 39.96° nM−1 has been observed. The surface morphology of sensor chip was also recorded using atomic force microscopy to confirm the presence of bound DENV E-protein into IgM surface.

The aim of this study is to prepare and study the cadmium sulfide quantum dot-graphene oxide-chitosan composite thin film. This composite material was coated on top of the gold layer by a spin-coating technique as a modification of the active layer for metal ion sensing using surface plasmon resonance spectroscopy (SPR). The composite material was prepared using a simple wet solution mixing method. An atomic force microscope (AFM) shows that the addition of GO increased the roughness of the composite thin film and the presence of CdS QDs cannot be observed as the size of the QDs are very small. The morphology of the nanocomposite material was observed using transmission electron microscopy (TEM). From the TEM images, it is observed that the materials mixed to form a nanocomposite material. The optical properties of the thin film via UV-Vis spectroscopy shows that the absorbance peaks of the thin film can be observed around 220 nm to near 300 nm, and the band gaps are around 4.0 eV. Lastly, the prepared thin film was tested as an active layer for metal ion detection via surface plasmon resonance (SPR), where the angle shift was observed to show that the prepared thin film has high potential for Co2+ ion detection.

An optical sensor based on surface plasmon resonance (SPR) phenomenon has been emerged for sensing a variety of analytes, including essential elements. It has numerous advantages, which include very high sensitivity, simple sample preparation, low cost, fast measurement capability, no requirement for reference solution, high reproducibility, ability to monitor kinetic behaviour, label-free detection, and nondestructive. The instrument and different developments on active layers or recognition molecules for sensitivity and selectivity improvements were explored. Further investigation in SPR optical sensor technology will expand SPR detection abilities and allow SPR sensing to be used widely including in environmental monitoring as an effective essential elements sensor in the future.

Combination of zinc oxide and white rice husk ash (ZnO0.60 – WRHA0.40) were prepared to produce zinc silicate glasses (Zn2SiO4) by conventional melt and quench technique at 1450 ˚C. X-Ray Fluorescent (XRF) results were being analyzed to confirm the chemical composition presents in WRHA sample. The glass behaviors were investigated using X-Ray Diffractometer (XRD). XRF shows that WRHA contains about 90% of silica dioxide (SiO2) while XRD shows that the glass amorphous nature phase was formed at composition of (ZnO0.60 – WRHA0.40). FESEM shows clear glassy surface which indicates the amorphous glass phase.

In this work, cadmium sulfide quantum dots composited with polyamidoamine (PAMAM) dendrimer (CdSQDs-PAMAM) thin film had been successfully developed for use in the detection of DENV E-proteins. The SPR results suggested that DENV E-protein can be detected in the range 0.0001 to 10 nM. The successful binding between antibodies and antigens in an immunoassay sensor was further confirmed using UV-Vis spectroscopy, by observing the red shift of absorption edge.

In this research, hexadecyltrimethylammonium bromide modified nanocrystalline cellulose/graphene oxide composite (CTA-NCC/GO) layer was prepared by using spin coating technique on gold-coated glass layer was prepared. The composite was used to detect copper ion using surface plasmon resonance spectroscopy and the sensor detection limit was 0.01 ppm until 0.5 ppm.

In this study, gold layer has been modified by introducing chitosan-graphene oxide-cadmium sulfide quantum dots on the gold layer for the detection of cobalt ion, Co2+. The composite material was deposited on the gold layer by using spin coater machine. The thin film was used as an active layer for the detection of Co2+ using surface plasmon spectroscopy and the optical changes of the thin film after contacting with different concentration of Co2+ ions had been obtained and graph fitted. The resonance angle shifted to a higher value as the concentration of Co2+ ions was increased. Changes of the resonance angle showed that Co2+ ion does react with the modified thin film with a binding affinity of 3.03 M-1.

In this study, the preparation of immobilized 4-(2-pyridylazo)resorcinol (PAR) in chitosan-graphene oxide composite has been described using spin coating technique. The optical properties of the composite thin film was characterized using UV–Vis-NIR absorption spectroscopy and its optical band gap was obtained. The characterization of the composite thin film was confirmed by the Fourier transform infrared spectrum obtained and the surface morphology of the composite thin film was observed using field emission scanning electron microscope (FESEM). Lastly, the experimental SPR curves were obtained for different concentration of Co2+ metal ion solution to study the potential of the composite for metal sensing. The sensor produces a linear response for higher concentration of Co2+ with a sensitivity of 0.00069° ppm−1. These results indicate that the composite thin film shows potential for the detection of Co2+ using surface plasmon resonance technique.

A series of MnO-doped zinc soda lime silica glass systems was prepared by a conventional melt and quenching technique. In this study, the x-ray diffraction analysis was applied to confirm the amorphous nature of the glasses. Fourier transform infrared spectroscopy shows the glass network consists of MnO4, SiO4, and ZnO4 units as basic structural units. The glass samples under field emission scanning electron microscopy observation demonstrated irregularity in shape and size with glassy phase-like structure. The optical absorption studies revealed that the optical bandgap (

A low cost method was employed to synthesize ZnO-SLS:xEu3+ phosphors using recyclable bottle glass as silica source. The structural and optical properties of ZnO-SLS:xEu3+ (x = 0, 1, 2, 3, 4 and 5 wt.%) glasses were determined using X-ray diffraction (XRD), Fourier transform infrared reflectance (FTIR), UV-visible (Uv-Vis) and photoluminescence (PL) spectroscopy. Structural investigation using XRD measurement had broadened the halo peak with the doping of dopants. FTIR spectra showed the glass system consists of –OH and SiO4 bands. Meanwhile, the optical measurement using UV-Vis absorption has been induced a blue shift of the electronic absorption edge. The emission peak intensity of ZnO-SLS:xEu3+ phosphors was enhanced with the progression of doping concentration and thus, revealed their potential as red emitting phosphors under 400 nm excitation.

In this paper, Zn2SiO4:xEu3+ phosphors were synthesized with different concentrations of Eu3+ ions (x = 1, 3 and 5 wt.%) by using waste bottle glasses as silicate source. The structure, morphology, and luminescent properties of the phosphors were characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and photoluminescence (PL) spectroscopy. The XRD analysis revealed that addition of dopant increased the crystallinity of the samples, and then were decreased dramatically when the dopant concentration further to 5 wt.%. The FESEM images showed the samples have irregular in shapes while their emission and excitation peak of Zn2SiO4:xEu3+ phosphor was observed at 600 and 400 nm, respectively.

To date, the demand for better light emitting diodes (LEDs) has led to growing interest in producing Zn2SiO4 based glass ceramic phosphors using waste materials. In this research, low cost Zn2SiO4:xEu3+ phosphors were prepared based on a solid state method using recyclable glass wastes as silica source. The influence of Eu3+ ions (x = 0, 1, 2, 3, 4 and 5 wt.%) and the effect of sintering temperatures, ranging from 600 to 1000 °C on the structural, morphological and optical properties of the phosphors were also investigated using X-ray diffraction (XRD), Field emission scanning electron microscopy (FESEM), Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, Ultraviolet-visible near infrared (UV-Vis-NIR) spectroscopy and Photoluminescence (PL) spectroscopy. These glass ceramics showed the increasing densities with increasing Eu3+ and sintering temperature. Structural investigation using XRD had revealed that the higher intensities of the diffraction peaks were due to sintering temperatures. Furthermore, their diffraction peaks had slightly shifted to lower diffraction angles when the dopant’s concentration was increased. The morphologies from FESEM analysis showed the formation of densely packed grains and smooth surfaces with the increment of sintering temperatures and addition of dopants. FTIR spectra showed that the progression of sintering temperature has narrowed the broad bands of SiO4 and ZnO4 at 1000 °C. All the broad bands were reduced to smaller bands after the addition of dopant. Additionally, the effects of sintering temperatures and dopants on the samples were apparent on the Raman spectra, which showed the narrow width of Raman lines and the shifted energy region in the spectrum. Most importantly, the largest optical band gaps of the samples were found at the highest sintering temperature. Meanwhile, Eu3+ doped samples have shown the largest optical band gap at 1000 °C upon the examination of the Moss- Burstein effect. Results for the pho

This paper presents a study on synthesis and optical properties of Zn2SiO4:1 wt% Eu3+ at different heat treatments. The objective of the research is to synthesize Zn2SiO4:1 wt% Eu3+ phosphor by using low cost solid state reaction method with recycled waste bottle glasses as the silicate source. The X-ray diffraction results showed that the prepared Zn2SiO4:1 wt% Eu3+ phosphors have a sharp diffraction peak as the heat treatment temperatures were increased from 600 to 1000 °C. Furthermore, the morphology from the Field emission scanning electron microscope analysis were shown the formation of well crystalline samples with dense packed grains due to the increment of heat treatment temperatures. Fourier transform infrared spectra has confirmed the present elements in Zn2SiO4:1 wt% Eu3+ phosphors while the narrow width of Raman line spectra were observed at temperatures ranging from 700 to 1000 °C indicates good homogeneity and crystallinity of synthesized powders. In addition, the energy band gap of europium doped zinc silicate increased dramatically up to 3.62 eV at temperature of 1000 °C. Photoluminescence measurements has also exhibited the red emission corresponding to the 5D0 → 7F2 (600 nm) when viewed under blue excitation.

In this study, the preparation of ionophore doped chitosan biopolymer solution using chitosan, glutaraldehyde and p-tert-butylcalix[4]arene-tetrakis(N,N-dimethylacetamide) in acetic acid under mild condition has been described. After the reaction, the ionophore doped chitosan biopolymer thin film was prepared using spin coating technique. The obtained chitosan derivative was confirmed and characterized by Fourier transform infrared spectroscopy (FTIR) and ultraviolet–visible near infra-red (UV–Vis–NIR) spectroscopy. Surface morphology, evaluated by atomic force microscopy (AFM), indicates the biopolymer thin film is relatively smooth and homogeneous. Absorption of the thin film is high with optical band gap of 3.177 eV. The incorporation of this derivative thin film with an optical spectroscopy can produce positive responses towards metal ion. This ionophore doped chitosan thin film can be considered as a novel optical material for practical application especially in the field of metal ion sensing.