Detection of phenol by incorporation of gold modified-enzyme based graphene oxide thin film with surface plasmon resonance technique

Determination of Phenol with Peroxidase Immobilized on CaCO3

Phenols are widely used in industries despite their toxicity, which requires governments to limit their concentration in water to 5 mg/L before discharge to the city sewer. Thus, it is essential to develop a rapid, simple, and low-cost detection method for phenol. This study explored two pathways of peroxidase immobilization to develop a phenol detection system: peroxidase encapsulation into polyelectrolyte microcapsules and peroxidase captured by CaCO3. The encapsulation of peroxidase decreased enzyme activity by 96%; thus, this method cannot be used for detection systems. The capturing process of peroxidase by CaCO3 microspherulites did not affect the maximum reaction rate and the Michaelis constant of peroxidase. The native peroxidase—Vmax = 109 µM/min, Km = 994 µM; CaCO3–peroxidase—Vmax = 93.5 µM/min, Km = 956 µM. Ultimately, a reusable phenol detection system based on CaCO3 microparticles with immobilized peroxidase was developed, capable of detecting phenol in the range of 700 ng/mL to 14 µg/mL, with an error not exceeding 5%, and having a relatively low cost and production time. The efficiency of the system was confirmed by determining the content of phenol in a paintwork product.

Practical and Rapid Membrane-Based Biosensor for Phenol Using Copper/Calcium-Enzyme Hybrid Nanoflowers

Phenol, a pollutant frequently found in chemical industries effluents, is highly toxic even in low concentrations. This study reports a green, simple, and rapid method for qualitative phenol biosensing using horseradish peroxidase (HRP) hybrid nanoflowers made with copper (Cu²⁺-hNF) or calcium (Ca²⁺-hNF) ions. The enzyme was immobilized through protein-inorganic self-assembly into hybrid structures and subsequently supported onto a polyvinylidene fluoride (PVDF) membrane. SEM, EDS, FTIR, and XRD techniques sustained the effective enzyme encapsulation into hybrid structures. The protein concentration in the structures was 0.25 mg.mL^-1 for both ions. The best temperature and pH were 60 °C and 7.4, respectively, for both hybrids and the free enzyme, suggesting that the immobilization did not affect the optimal conditions of the free HRP. Thermal stability from 25 to 70 °C and pH stability from 4.0 to 9.0 of the hybrids were also determined. Finally, using copper and calcium hybrids, both biosensors produced onto a PVDF membrane could detect phenol in concentrations ranging from 0.72 to 24.00 µmol.mL^-1 in 1 min. In contrast, control biosensors produced with free enzyme have not presented a visible color change in the same conditions. The findings suggest a promising application of the developed biosensors in functional phenol detection.

Plasmonic Refractive Index Sensor Enhanced with Chitosan/Au Bilayer Thin Film for Dopamine Detection

Surface plasmonic sensors have received considerable attention, found extensive applications, and outperformed conventional optical sensors. In this work, biopolymer chitosan (CS) was used to prepare the bilayer structure (CS/Au) of a plasmonic refractive index sensor for dopamine (DA) detection. The sensing characteristics of the developed plasmonic sensor were evaluated. Increasing DA concentrations significantly shifted the SPR dips. The sensor exhibited stability and a refractive index sensitivity of 8.850°/RIU in the linear range 0.1 nM to 1 µM with a detection limit of 0.007 nM and affinity constant of 1.383 × 10⁸ M^-1. The refractive index and thickness of the CS/Au structure were measured simultaneously by fitting the obtained experimental findings to theoretical data based on Fresnel equations. The fitting yielded the refractive index values n (1.5350 ± 0.0001) and k (0.0150 ± 0.0001) for the CS layer contacting 0.1 nM of DA, and the thickness, d was (15.00 ± 0.01) nm. Then, both n and d values increased by increasing DA concentrations. In addition, the changes in the FTIR spectrum and the variations in sensor surface roughness and structure obtained by AFM analysis confirmed DA adsorption on the sensing layer. Based on these observations, CS/Au bilayer has enhanced the performance of this plasmonic sensor, which showed promising importance as a simple, low-cost, and reliable platform for DA sensing.

Structural and Optical Properties of Graphene Quantum Dots-Polyvinyl Alcohol Composite Thin Film and Its Potential in Plasmonic Sensing of Carbaryl

In this study, graphene quantum dots (GQDs) and polyvinyl alcohol (PVA) composite was prepared and then coated on the surface of gold thin film via the spin coating technique. Subsequently, Fourier transform infrared spectroscopy (FT-IR), atomic force microscopy (AFM), and ultraviolet-visible spectroscopy (UV-Vis) were adopted to understand the structure, surface morphology, and optical properties of the prepared samples. The FT-IR spectral analysis revealed important bands, such as O-H stretching, C=O stretching, C-H stretching, and O=C=O stretching vibrations. The surface roughness of the GQDs-PVA composite thin film was found to be increased after exposure to carbaryl. On the other hand, the optical absorbance of the GQDs-PVA thin film was obtained and further analysis was conducted, revealing a band gap E_g value of 4.090 eV. The sensing potential of the thin film was analyzed using surface plasmon resonance (SPR) spectroscopy. The findings demonstrated that the developed sensor's lowest detection limit for carbaryl was 0.001 ppb, which was lower than that previously reported, i.e., 0.007 ppb. Moreover, other sensing performance parameters, such as full width at half maximum, detection accuracy, and signal-to-noise ratio, were also investigated to evaluate the sensor's efficiency.

Smartphone-based Surface Plasmon Resonance Sensors: a Review

The surface plasmon resonance (SPR) is a phenomenon based on the combination of quantum mechanics and electromagnetism, which leads to the creation of charge oscillations on a metal-dielectric interface. The SPR phenomenon creates a signal which measures refractive index change at the metal-dielectric interface. SPR-based sensors are being developed for real-time and label-free detection of water pollutants, toxins, disease biomarkers, etc., which are highly sensitive and selective. Smartphones provide hardware and software capability which can be incorporated into SPR sensors, enabling the possibility of economical and accurate on-site portable sensing. The camera, screen, and LED flashlight of the smartphone can be employed as components of the sensor. The current article explores the recent advances in smartphone-based SPR sensors by studying their principle, components, application, and signal processing. Furthermore, the general theoretical and practical aspects of SPR sensors are discussed.

Direct and Sensitive Detection of Dopamine Using Carbon Quantum Dots Based Refractive Index Surface Plasmon Resonance Sensor

Abnormality of dopamine (DA), a vital neurotransmitter in the brain’s neuronal pathways, causes several neurological diseases. Rapid and sensitive sensors for DA detection are required for early diagnosis of such disorders. Herein, a carbon quantum dot (CQD)-based refractive index surface plasmon resonance (SPR) sensor was designed. The sensor performance was evaluated for various concentrations of DA. Increasing DA levels yielded blue-shifted SPR dips. The experimental findings revealed an excellent sensitivity response of 0.138°/pM in a linear range from 0.001 to 100 pM and a high binding affinity of 6.234 TM⁻¹. The effects of varied concentrations of DA on the optical characteristics of CQD thin film were further proved theoretically. Increased DA levels decreased the thickness and real part of the refractive index of CQD film, according to fitting results. Furthermore, the observed reduction in surface roughness using AFM demonstrated that DA was bound to the sensor layer. This, in turn, explained the blue shift in SPR reflectance curves. This optical sensor offers great potential as a trustworthy solution for direct measurement due to its simple construction, high sensitivity, and other sensing features.

Evaluation of Structural and Optical Properties of Graphene Oxide-Polyvinyl Alcohol Thin Film and Its Potential for Pesticide Detection Using an Optical Method

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.

Femtomolar detection of dopamine using surface plasmon resonance sensor based on chitosan/graphene quantum dots thin film

Due to the crucial role of dopamine (DA) in health and peripheral nervous systems, it is particularly important to develop an efficient and accurate sensor to monitor and determine DA concentrations for diagnostic purposes and diseases prevention. Up to now, using surface plasmon resonance (SPR) sensors in DA determination is very limited and its application still at the primary stage. In this work, a simple and ultra-sensitive SPR sensor was constructed for DA detection by preparation of chitosan- graphene quantum dots (CS-GQDs) thin film as the sensing layer. Other SPR measurements were conducted using different sensing layers; GQDs, CS for comparison. The proposed thin films were prepared by spin coating technique. The developed CS-GQDs thin film-based SPR sensor was successfully tested in DA concentration range from 0 fM to 1 pM. The designed SPR sensor showed outstanding performance in detecting DA sensitively (S = 0.011°/fM, R² = 0.8174) with low detection limit of 1.0 fM has been achieved for the first time. The increased angular shift of SPR dip, narrow full width half maximum of the SPR curves, excellent signal-to-noise ratio and figure of merit, and a binding affinity constant (K_A) of 2.962 PM^-1 demonstrated the potential of this sensor to detect DA with high accuracy. Overall, it was concluded that the proposed sensor would serve as a valuable tool in clinical diagnostic for the serious neurological disorders. This in turns has a significant socio-economic impact.

Advanced Optical Sensing of Phenolic Compounds for Environmental Applications

Phenolic compounds are particularly dangerous due to their ability to remain in the environment for a long period of time and their toxic effects. They enter in the environment in different ways, such as waste from paper manufacturing, agriculture (pesticides, insecticides, herbicides), pharmaceuticals, the petrochemical industry, and coal processing. Conventional methods for phenolic compounds detection present some disadvantages, such as cumbersome sample preparation, complex and time-consuming procedures, and need of expensive equipment. Therefore, there is a very large interest in developing sensors and new sensing schemes for fast and easy-to-use methods for detecting and monitoring the phenolic compound concentration in the environment, with special attention to water. Good analytical properties, reliability, and adaptability are required for the developed sensors. The present paper aims at revising the most generally used optical methods for designing and fabricating biosensors and sensors for phenolic compounds. Some selected examples of the most interesting applications of these techniques are also proposed.

Recent Developments in Plasmonic Sensors of Phenol and Its Derivatives

Many scientists are increasingly interested in on-site detection methods of phenol and its derivatives because these substances have been universally used as a significant raw material in the industrial manufacturing of various chemicals of antimicrobials, anti-inflammatory drugs, antioxidants, and so on. The contamination of phenolic compounds in the natural environment is a toxic response that induces harsh impacts on plants, animals, and human health. This mini-review updates recent developments and trends of novel plasmonic resonance nanomaterials, which are assisted by various optical sensors, including colorimetric, fluorescence, localized surface plasmon resonance (LSPR), and plasmon-enhanced Raman spectroscopy. These advanced and powerful analytical tools exhibit potential application for ultrahigh sensitivity, selectivity, and rapid detection of phenol and its derivatives. In this report, we mainly emphasize the recent progress and novel trends in the optical sensors of phenolic compounds. The applications of Raman technologies based on pure noble metals, hybrid nanomaterials, and metal–organic frameworks (MOFs) are presented, in which the remaining establishments and challenges are discussed and summarized to inspire the future improvement of scientific optical sensors into easy-to-operate effective platforms for the rapid and trace detection of phenol and its derivatives.

2D material assisted SMF-MCF-MMF-SMF based LSPR sensor for creatinine detection

The purpose of this work is to propose a simple, portable, and sensitive biosensor structure based on singlemode fiber-multicore fiber-multimode fiber-singlemode fiber (SMF-MCF-MMF-SMF) for the detection of creatinine in the human body. Chemical etching has been used to modify the diameter of the sensing probe to approximately 90 μm in order to generate strong evanescent waves (EWs). The sensor probe is functionalized with graphene oxide (GO), gold nanoparticles (AuNPs), molybdenum disulfide nanoparticles (MoS₂-NPs), and creatininase (CA) enzyme. The concentration of creatinine is determined using fiber optic localized surface plasmon resonance (LSPR). While EWs are used to enhance the LSPR effect of AuNPs, two-dimensional (2D) materials (GO and MoS₂-NPs) are used to increase biocompatibility, and CA is used to increase probe specificity. Additionally, HR-TEM and UV-visible spectroscopy are used to characterize and measure the nanoparticle (NP) morphology and absorption spectrum, respectively. SEM is used to characterize the NPs immobilized on the surface of the fiber probe. The sensor probe's reusability, reproducibility, stability, selectivity, and pH test results are also tested to verify the sensor performance. The sensitivity of proposed sensor is 0.0025 nm/μM, has a standard deviation of 0.107, and has a limit of detection of 128.4 μM over a linear detection range of 0 - 2000 μM.

Sensing Methods for Hazardous Phenolic Compounds Based on Graphene and Conducting Polymers-Based 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.

Exploration on Structural and Optical Properties of Nanocrystalline Cellulose/Poly(3,4-Ethylenedioxythiophene) Thin Film for Potential Plasmonic Sensing Application

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.

Recent Advances on Detection of Insecticides Using Optical Sensors

Insecticides are enormously important to industry requirements and market demands in agriculture. Despite their usefulness, these insecticides can pose a dangerous risk to the safety of food, environment and all living things through various mechanisms of action. Concern about the environmental impact of repeated use of insecticides has prompted many researchers to develop rapid, economical, uncomplicated and user-friendly analytical method for the detection of insecticides. In this regards, optical sensors are considered as favorable methods for insecticides analysis because of their special features including rapid detection time, low cost, easy to use and high selectivity and sensitivity. In this review, current progresses of incorporation between recognition elements and optical sensors for insecticide detection are discussed and evaluated well, by categorizing it based on insecticide chemical classes, including the range of detection and limit of detection. Additionally, this review aims to provide powerful insights to researchers for the future development of optical sensors in the detection of insecticides.

Nonlinear interferometric surface-plasmon-resonance sensor

A nonlinear interferometer can be constructed by replacing the beam splitter in the Mach-Zehnder interferometer with four-wave mixing (FWM) process. Meanwhile, the conventional surface plasmon resonance (SPR) sensors can be extensively used to infer the information of refractive index of the sample to be measured via either angle demodulation technique or intensity demodulation technique. Combined with a single FWM process, a quantum SPR sensor has been realized, whose noise floor is reduced below standard quantum limit with sensitivity unobtainable with classical SPR sensor. Therefore, in this work we have theoretically proposed a nonlinear interferometric SPR sensor, in which a conventional SPR sensor is placed inside nonlinear interferometer, which is called as I-type nonlinear interferometric SPR sensor. We demonstrate that near resonance angle I-type nonlinear interferometric SPR sensor has the following advantages: its degree of intensity-difference squeezing, estimation precision ratio, and signal-noise-ratio are improved by the factors of 4.6 dB, 2.3 dB, and 4.6 dB respectively than that obtained with a quantum SPR sensor based on a single FWM process. In addition, the theoretical principle of this work can also be expanded to other types of sensing, such as bending, pressure, and temperature sensors based on a nonlinear interferometer.

Cellulose and Vanadium Plasmonic Sensor to Measure Ni2+ Ions

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.

Clinical Application for Screening Down's Syndrome by Using Carboxylated Graphene Oxide-Based Surface Plasmon Resonance Aptasensors

BACKGROUND

Advanced medical detection technology requires high sensitivity and accuracy to increase the disease detection rate. We showed that carboxyl-functionalized graphene oxide (carboxyl-GO) biosensing materials are capable of accurate detection.

METHODS

We developed a carboxylated GO-based surface plasmon resonance (SPR) aptasensor suitable for screening Down's syndrome in clinical serum. This biosensing material could rapidly and accurately detect hCG protein with a low concentration to identify fetal Down's syndrome. The developed carboxyl-GO-based SPR aptasensor showed excellent sensitivity and limit of detection without the use of antibodies and without any specific preference.

RESULTS

hCG protein detection limits of 1 pM in buffer samples and 1.9 pM in clinical serum samples were achieved. The results showed that the carboxyl-GO-based chip could detect hCG well below the normal physiological level of serum protein (5.0 mIU/mL). High affinity, sensitivity, and better detection limit were obtained in the range of 1.9 pM to 135 pM. The results showed a 5k-fold dilution factor, and that an SPR angle shift of more than 20 millidegrees (mo) was associated with a significant risk of fetal Down's syndrome compared to normal pregnant women. The results clearly showed that the detection of hCG protein in serum samples from pregnant women at 12-19 weeks could be used to screen Down's syndrome with high selectivity and sensitivity.

CONCLUSION

Our findings suggest the potential application of carboxyl-GO film in proof-of-concept studies for serum assays as a new type of SPR material. In addition, peptide and carboxyl-GO films may be conducive to the development of future point of care testing and rapid diagnostic devices for other diseases such as cancer.

Cationically Modified Nanocrystalline Cellulose/Carboxyl-Functionalized Graphene Quantum Dots Nanocomposite Thin Film: Characterization and Potential Sensing Application

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 plasmon resonance phenomenon. This work suggests that the novel nanocomposite thin film has potential for a sensing application in glucose detection.

Enhanced sensitivity in graphene-based SPR biosensors using electrical bias

A theoretical framework to increase the sensitivity of graphene-based surface plasmon resonance (SPR) biosensors by the application of electrical bias voltage across the sensor surface is presented. Graphene layers deposited on thin gold film (50 nm) form the sensor surface system where the surface plasmon is excited. The real and imaginary parts of the refractive index of this gold-graphene system can be controlled by tuning its chemical potential using electrical modulation. Numerical calculations show a promising method to enhance the sensitivity of graphene-based SPR biosensors.