A unique “turn-on” fluorescence signalling strategy for highly specific detection of ascorbic acid using carbon dots as sensing probe

Carbon dots (CDs) that showed strong blue fluorescence were successfully synthesised from sodium alginate via furnace pyrolysis. The single step pyrolytic synthesis was simple to perform while yielded CDs with high photostability, good water solubility and minimum by-products. In order to design the probe with “turn-on” sensing capability, the CDs were screened against a series of metal cations to first “turn-off” the fluorescence. It was found that ferric ions (Fe3þ) were most responsive and effective in quenching the fluorescence of CDs. Based on this observation, the conditioning of the probe was performed to ensure the fluorescence was completely quenched, while not overloading the system with Fe3þ. At the optimised condition, the CDs-Fe3þ mixture served as a highly specific detection probe for ascorbic acid (AA). The analytical potential of the probe was evaluated and showed a good linear range of response for AA concentration of 24–40 μg/mL. The selectivity study against other possible co-existing species was carried out and proved that our unique “turn-on” fluorescence signalling strategy was highly effective and selective towards AA as the target analyte. The probe was demonstrated for quantification of AA in real samples, which was the commercially available vitamin C supplement. The result showed good accuracy with minimum deviation from standard method adopted for validation purpose

Corrigendum to “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 12V 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 0.45mM (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

Detection of Sn(II) ions via quenching of the fluorescence of carbon nanodots

Abstract We report that fluorescent carbon nanodots (Cdots) can act as an optical probe for quantifying Sn(II) ions in aqueous solution. C-dots are synthesized by carbonization and surface oxidation of preformed sago starch nanoparticles. Their fluorescence is significantly quenched by Sn(II) ions, and the effect can be used to determine Sn(II) ions. The highest fluorescence intensity is obtained at a concentration of 1.75 mM of C-dots in aqueous solution. The probe is highly selective and hardly interfered by other ions. The quenching mechanism appears to be predominantly of the static (rather than dynamic) type. Under optimum conditions, there is a linear relationship between fluorescence intensity and Sn(II) ions concentration up to 4 mM, and with a detection limit of 0.36 μM

Facile synthesis of fluorescent carbon nanodots from starch nanoparticles

Fluorescent carbon dots were synthesized by the carbonization of preformed native sago starch nanoparticles, followed by surface oxidation in an aqueous medium. The morphology and particle sizes of carbon nanodots (CDs) were observed to be very similar to starch nanoparticles that were used as precursors. The particle sizes of CDs synthesized in this study were within the range 50–80 nm, which were much larger than those of very tiny CDs (1–5 nm) previously reported. The CDs portrayed fluorescent with constant emission wavelength peak at 430 nm when excited with various higher energy photons. The non-shifting of the emission wavelength peak suggested that CDs prepared in this study were highly homogenous and possessed mono-dispersed physiochemical properties

Sustainable alternative in environmental monitoring using carbon nanoparticles as optical probes

Environmental monitoring is getting more important nowadays due to the greater stress faced by the natural environment in the era of urbanisation and industrialisation. To accomplish the task, rapid and reliable analytical probes are essentially needed to perform the monitoring at real time basis with high sensitivity and accuracy. In view of this, analytical probes developed using carbon nanoparticles are one of the latest alternatives that are proven with capability to detect various analytes of the environment. Carbon nanoparticles portray good fluorescence property that enables the integration onto optical sensing transducers. Further engineering via surface functionalization can be performed in the interest to improve the selectivity and sensitivity of the probes. There are several advantages of using carbon nanoparticles and the most significant benefit is the sustainability prospect as compared to other groups of fluorophores. Carbon nanoparticles can be synthesised with greener approach via simple pyrolysis or hydrolysis processes that involve minimum use of toxic or harmful starting precursors, besides able to tap on using renewable resources such as carbon rich agricultural wastes. The synthesis is often performed under mild condition and produces less or no side chemical products. Carbon nanoparticles by nature show low toxicity effect to the environment. This review focuses specifically of the sustainable significances, advantages and achievements in adopting carbon nanoparticles as an alternative for environmental monitoring

Portable NMR-based sensors in medical diagnosis

Nuclear magnetic resonance (NMR) is a well-established analytical method used for qualitative and quantitative analyses in various areas and applications. It utilizes a phenomenon where nuclei of a certain atom is resonating at a specific secondary oscillating magnetic field under a strong static magnetic field. The energy absorbed during resonance is highly specific and governed by the micro magnetic environment of the nuclei. During the early stage of development, NMR analyses were performed in laboratory by placing the sample of interest inside a strong stationary magnet. Then it followed by monitoring the absorption frequency occurred on the secondary radio-wave directed to the sample. In order to obtain high resolution in the absorption frequency, high magnetic field is required and often generated using superconductor wire surrounded with cooling coils. Although the configuration produces accurate results, the instrument is rather large, heavy, and non-portable. This has made the practical utilization less possible for on-site applications or for samples having sizes larger that the core of the permanent magnet. Continuous development based on the fundamental principle of NMR has resulted in great advancement in hardware and the detection sensitivity. One of the most remarkable achievements will be the development of portable NMR-based sensors. This class of sensor is far more flexible due to its smaller size and suits on-site in situ measurements. Furthermore, such sensors are cheaper to develop and less costly to maintain as compared to the conventional instruments. However, the sensors have lower resolution as due the weaker magnetic field generated from smaller permanent magnets. Despite this, the results recorded are still significantly useful. Data analysis and optimization of the sensor configuration can be employed to achieve better resolution. For instance, the NMR-MOUSE is one of the portable NMR-based sensor types that can be used for bio-imaging and characterization of polymers. This chapter discusses some fundamental developments of the portable NMR-based sensors and its practical application in the field of medical diagnosis. Future prospects and challenges faced in this area are highlighted

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