Sing Muk Ng

Synthesis of fluorescent carbon dots via simple acid hydrolysis of bovine serum albumin and its potential as sensitive sensing probe for lead (II) ions

Carbon dots have great potential to be utilised as an optical sensing probe due to its unique photoluminescence and less toxic properties. This work reports a simple and novel synthesis method of carbon dots via direct acid hydrolysis of bovine serum albumin protein in a one-pot approach. Optimisation of the important synthetic parameters has been performed which consists of temperature effect, acid to protein ratio and kinetics of reaction. Higher temperature has promoted better yield with shorter reaction time. The carbon dots obtained shows a strong emission at the wavelength of 400 nm with an optimum excitation of 305 nm. The potential of the carbon dots as optical sensing probe has been investigated on with different cations that are of environmental and health concern. The fluorescence of the carbon dots was significantly quenched particularly by lead (II) ions in a selective manner. Further analytical study has been performed to leverage the performance of the carbon dots for lead (II) ions sensing using the standard Stern-Volmer relationship. The sensing probe has a dynamic linear range up to 6.0 mM with a Stern-Volmer constant of 605.99 M(-1) and a limit of detection (LOD) of 5.05 μM. The probe performance was highly repeatable with a standard deviation below 3.0%. The probe suggested in this study demonstrates the potential of a more economical and greener approach that uses protein based carbon dots for sensing of heavy metal ions.

A review on fluorescent inorganic nanoparticles for optical sensing applications

Fluorescence is one of the techniques adopted for a large number of optical bioassays and chemical sensing probes. The key driving motivation is basically governed by the ease of operational process, simple setup, high sensitivity, online throughput readouts, and most importantly the well understood principles behind fluorescence spectroscopy. Typically, an optical sensor adopting this technique requires sensing receptors that will interact with an analyte, subsequently causing a change that can be correlated to the identity and/or quantity of the analyte of interest. For this instance, various fluorophores are suitable to be used as the receptor and the most recent class is the fluorescent inorganic nanoparticles; portraying similar fluorescence properties to conventional organic dyes, but having special features and nature that are unique by themselves. This paper offers a rational review particularly on the development of these fluorescent inorganic nanoparticles in the area of optical sensing, excluding the coverage on fluorescent nanoparticles made of organic based fluorophores. It will cover the fundamental properties, basic methods of synthesis, engineering features, and the available characterisation options of the nanoparticles. Specifically, the application aspects for use as optical sensing receptors is highlighted with the focus on the possible sensing mechanisms, the crucial optimisation processes during the development of a sensor, and the options available for data analysis on the signals recorded from the optical sensors. Various successful demonstrations of the utilisation of such fluorescent nanoparticles for detecting different analytes will be given in this review. This paper offers a good insight on real practical ways to utilise the unique optical properties of fluorescent inorganic nanoparticles for sensing applications.

Novel microencapsulation of potential drugs with low molecular weight and high hydrophilicity: hydrogen peroxide as a candidate compound.

Microencapsulation of drugs into solid biodegradable polymeric microspheres via solvent evaporation technique remains challenging especially with those having low molecular weight and high hydrophilicity nature. This paper presents an efficient encapsulation protocol for this group of drugs, demonstrated using hydrogen peroxide as a model compound that is encapsulated into poly(lactic-co-glycolic acid) microspheres. Hydrogen peroxide can be employed as antiseptic agent or its decomposed form into oxygen can be useful in various pharmaceutical applications. The new encapsulation technique was developed based on the modification of conventional double emulsion and solvent evaporation protocol with a backward concentration gradient of hydrogen peroxide. This was achieved by adding and controlling the concentration of hydrogen peroxide at the continuous phase during the solidification stage of the microspheres. Parameters involved in the production and the formulation aspect were optimized to achieve the best protocol having controlled efficiency of encapsulation that is simple, safe, practical, and economical. Evaluation on the encapsulation efficiency and the release profile has been made indirectly by monitoring the dissolved oxygen level of the solution where the microspheres were incubated. Morphology of the microspheres was investigated using scanning electron microscopy. This proposed method has successfully used to prepare batches of microspheres having different encapsulation efficiencies and its potential applications have been demonstrated accordingly.

Fluorescein-labeled starch maleate nanoparticles as sensitive fluorescent sensing probes for metal ions

Fluorescein 5(6)-isothiocyanate starch maleate (FISM) nanoparticles were prepared by covalently attached fluorescein 5(6)- isothiocyanate (FITC) with starch maleate. FISM nanoparticles with a mean particle size of 87 nm were formed via selfassembly upon precipitation in ethanolic solution. FISM nanoparticles were strongly fluorescent with maximum emission wavelength of 518 nm. The fluorescence of FISM nanoparticles can be quenched by silver (Ag+) and lead (Pb2+) ions in a concentration dependent manner. We have demonstrated the first use of FISM nanoparticles as cheap and effective fluorescent sensing probes for Ag+ and Pb2+ ions with detection limits as low as 2.55 × 10-5M and 3.64 × 10-5 M, respectively.

An enzyme-modulated oxygen-producing micro-system for regenerative therapeutics

This study suggests the idea of treating oxygen as a drug in a biological environment and demonstrates that it will exhibit a dosage-dependent trend. To accomplish this, a micro-system was fabricated, having hydrogen peroxide as the oxygen-generating source, which was decomposed using catalase, a common enzyme found in nearly all living organisms. The relevance of the proposed micro-system was justified using cell viability assays under well-controlled and fixed conditions. This study was performed under two controlled conditions, normoxia and hypoxia, and tests were carried out using three different configurations of samples under each condition: direct addition of H(2)O(2), H(2)O(2) encapsulated with single layer, and H(2)O(2) encapsulated with double layers. This study demonstrates that the elegantly designed micro-system managed to control the decomposition of H(2)O(2) and avoided direct contact with cells, while also maintaining cell viability under a low oxygen environment.

Integrated miniature fluorescent probe to leverage the sensing potential of ZnO quantum dots for the detection of copper (II) ions

Quantum dots are fluorescent semiconductor nanoparticles that can be utilised for sensing applications. This paper evaluates the ability to leverage their analytical potential using an integrated fluorescent sensing probe that is portable, cost effective and simple to handle. ZnO quantum dots were prepared using the simple sol-gel hydrolysis method at ambient conditions and found to be significantly and specifically quenched by copper (II) ions. This ZnO quantum dots system has been incorporated into an in-house developed miniature fluorescent probe for the detection of copper (II) ions in aqueous medium. The probe was developed using a low power handheld black light as excitation source and three photo-detectors as sensor. The sensing chamber placed between the light source and detectors was made of 4-sided clear quartz windows. The chamber was housed within a dark compartment to avoid stray light interference. The probe was operated using a microcontroller (Arduino Uno Revision 3) that has been programmed with the analytical response and the working algorithm of the electronics. The probe was sourced with a 12 V rechargeable battery pack and the analytical readouts were given directly using a LCD display panel. Analytical optimisations of the ZnO quantum dots system and the probe have been performed and further described. The probe was found to have a linear response range up to 0.45 mM (R(2)=0.9930) towards copper (II) ion with a limit of detection of 7.68×10(-7) M. The probe has high repeatable and reliable performance.

Accurate Zirconium Detection at Visible Wavelength Using Artificial Neural Network

Abstract A quantitative analysis has been carried out to determine the concentration of Zr4+ ion in aqueous solution by using alizarin red S (ARS) as reagent to form ARS‐Zr complex. ARS‐Zr complex gives a maximum absorption peak at wavelength of 520 nm with pH 2.5. The repeatability study at two different Zr4+ ion concentrations of 10 mg/l and 200 mg/l was found to give RSD values of 1.16% and 0.55%, respectively. The study of interfering ions was carried out with K+, Na+, Ca2+, Pb2+, Al3+ and Fe3+ ions with Zr4+ ion: interfering ions at mole ratio of 1:1, 1:10 and 1:100. The study showed a significant interfering effect at the ratio of 1:100 for all the ions except K+ and Na+ ions. Characterization of ARS‐Zr complex gives a dynamic Zr4+ concentration range of 5–35 mg/l. However, the use of artificial neural network (ANN) was able to extend the dynamic concentration range of Zr4+ to a larger range of 5–200 mg/l with optimized ANN parameters of 14 hidden neurons, 20 epochs, and training rate of 0.001. The sum square error (SSE) was found to have a value of 0.33 with an average error of 0.38.

Molecularly imprinted polymers as optical sensing receptors: Correlation between analytical signals and binding isotherms

Despite the increasing number of usage of molecularly imprinted polymers (MIPs) in optical sensor application, the correlation between the analytical signals and the binding isotherms has yet to be fully understood. This work investigates the relationship between the signals generated from MIPs sensors to its respective binding affinity variables generated using binding isotherm models. Two different systems based on the imprinting of metal ion and organic compound have been selected for the study, which employed reflectance and fluorescence sensing schemes, respectively. Batch binding analysis using the standard binding isotherm models was employed to evaluate the affinity of the binding sites. Evaluation using the discrete bi-Langmuir isotherm model found both the MIPs studied have generally two classes of binding sites that was of low and high affinities, while the continuous Freundlich isotherm model has successfully generated a distribution of affinities within the investigated analytical window. When the MIPs were incorporated as sensing receptors, the changes in the analytical signal due to different analyte concentrations were found to have direct correlation with the binding isotherm variables. Further data analyses based on this observation have generated robust models representing the analytical performance of the optical sensors. The best constructed model describing the sensing trend for each of the sensor has been tested and demonstrated to give accurate prediction of concentration for a series of spiked analytes.

Synthesis of carbon nanoparticles from waste rice husk used for the optical sensing of metal ions

Abstract This work reports on a synthesis of carbon nanoparticles (CNPs) from waste rice husk by thermally-assisted carbonization in the presence of concentrated sulfuric acid. The fluorescent emmision characteristics of the CNPs, their quenching effects by metal ions and their use as a sensing material for Sn(II) ions were investigated. Results indicated that the yield of CNPs was optimized at a sulphuric acid concentration of 12 mol/L, heating temperature of 120 °C and heating time of 30 min. The sample showed a strong blue luminescence in water with a maximum emission at 439 nm. The fluorescence can be quenched by adding various metal ions by the formation of complexes between the metal ions and surface of the CNPs. Sn(II) ions had the most significant quenching effect on the fluorescence of the CNPs, which is concentration-dependent. The concentration dependent quenching was linearized with the Stern-Volmer equation, and showed a linear response up to a Sn(II) concentration of 6.13 mmol/L. The limit of detection for Sn(II) ions is 18.7 µmol/L with good repeatability.

Interface Study on Zinc Oxide Quantum Dots Using Fluorometric and Regression Analysis in View of Optical Sensing

A study has been performed to investigate the interface property of zinc oxide quantum dots (ZnO-Qdots) for optical sensing ability. Bare and L-cysteine capped ZnO-Qdots were prepared using simple sol-gel hydrolysis method at ambient conditions and the surface property was evaluated using a fluorometric technique. Data were interpreted and modeled using regression analysis, taking into account the effect of temperature and quencher concentration. The capping of L-cysteine caused the fluorescent yield to decrease up to 16-fold as compared to the bare ZnO-Qdots. Upon addition of an external quencher, emission of both bare and capped samples was quenched accordingly and dependent upon the concentration of the quencher. Regression analysis has confirmed with a significant low p-value (<0.05) that bare ZnO-Qdots obtained a dynamic quenching mechanism in the presence of copper (II) ion. Conversely, the capped ZnO-Qdots had a static quenching mechanism. Based on the interface mechanism understanding, it was found that capping effort reduced the sensing sensitivity while the bare one portrayed good sensing potential with a detection limit down to 41.30 ± 0.05 nM. A multi-variable model was constructed for the bare ZnO-Qdots and successfully predicted the concentration of copper (II) ion accurately even at different temperature conditions.