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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.

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.

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.

As a new promising carbonic nanomaterial with a lot of outstanding advantages, graphene quantum dots (GQDs) opened up a new field for the development of excellent sensors. Herein, the preparation of hydroxyl-functionalized graphene quantum dots (HGQDs) based thin film with different materials that are chitosan and cetyltrimethylammonium bromide (CTAB) have been described namely chitosan/hydroxyl-functionalized graphene quantum dots (Cs/HGQDs) thin film and cetyltrimethylammonium bromide/hydroxyl-functionalized graphene quantum dots (CTAB/HGQDs) thin film. The Cs/HGQDs and CTAB/HGQDs were deposited homogenously using the spin coating technique. The synthesized thin films were then characterized using Fourier transform infrared spectroscopy (FTIR) to confirm the existence of functional groups in the composites such as hydroxyl, carboxyl, and carboxylic acid. From the atomic force microscope (AFM) analysis, the addition of chitosan and CTAB increased the roughness of the thin films. Meanwhile, the optical properties of the thin films were studied using UV-Vis absorption spectroscopy and photoluminescence (PL) spectroscopy. The absorbance peaks of Cs/HGQDs and CTAB/HGQDs thin films can be observed around the wavelength of 270 nm to 300 nm with optical band gap values of 3.80 eV and 4.16 eV, respectively. Moreover, the intensity of PL spectra for both thin films were noticed around the wavelength of 420 nm to 450 nm. The development of optical sensors for heavy metal ions detection has been rapidly growing. However, the current methods suffer limitations which then led to the emergence of an outstanding technique called surface plasmon resonance (SPR) spectroscopy. In this study, the as developed thin films have been incorporated with SPR for the detection of ferric ion (Fe3+). The sensors produce positive responses upon exposure to Fe3+ of various concentration. At lower Fe3+ concentration, the CTAB/HGQDs thin film showed higher sensitivity equals to 29.886° ppm-1 compa

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

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.

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.