Sensitive and selective electrochemical detection of artemisinin based on its reaction with p-aminophenylboronic acid

Self-Immolative Electrochemical Redox Substrates: Emerging Artificial Receptors in Sensing and Biosensing

The development of artificial receptors has great significance in measurement science and technology. The need for a robust version of natural receptors is getting increased attention because the cost of natural receptors is still high along with storage difficulties. Aptamers, imprinted polymers, and nanozymes are some of the matured artificial receptors in analytical chemistry. Recently, a new direction has been discovered by organic chemists, who can synthesize robust, activity-based, self-immolative organic molecules that have artificial receptor properties for the targeted analytes. Specifically designed trigger moieties implant selectivity and sensitivity. These latent electrochemical redox substrates are highly stable, mass-producible, inexpensive, and eco-friendly. Combining redox substrates with the merits of electrochemical techniques is a good opportunity to establish a new direction in artificial receptors. This Review provides an overview of electrochemical redox substrate design, anatomy, benefits, and biosensing potential. A proper understanding of molecular design can lead to the development of a library of novel self-immolative redox molecules that would have huge implications for measurement science and technology.

Ratiometric fluorescence detection of artemisinin based on photoluminescent Zn-MOF combined with hemin as catalyst

Artemisinin (ART) is a type of frontline drug to treat drug-resistant falciparum malaria. Simple, accurate and selective determination of ART is significant to monitor its clinical pharmaceutical efficacy. Herein, a new ratiometric fluorescence method has been designed for the determination of ART with Zn-MOF as fluorescence reference and hemin as catalyst, respectively. Zn-MOF possesses intrinsic fluorescence at 443 nm owing to 2-aminoterephthalic acid ligand. When o-phenylenediamine (OPD) is mixed with hemin, a weak fluorescent signal at 570 nm ascribed to oxidized product of OPD (oxOPD) is observed. In the presence of ART, hemin can catalyze ART to break its peroxide bridge and release a large number of reactive oxygen species, which effectively oxidize OPD into luminescent oxOPD. Therefore, the fluorescence at 570 nm is enhanced significantly while the fluorescence of Zn-MOF remains basically unchanged. Thus, a ratiometric fluorescence sensing platform has been constructed for the detection of ART. This method exhibits wider linear range (0.15 μM-150 μM) with detection limit of 50 nM. This novel and selective method has been used to detect ART in compound naphthoquinone phosphate tablets.

An electrochemical sensor for the voltammetric determination of artemisinin based on carbon materials and cobalt phthalocyanine

An electrochemical sensor for the determination of artemisinin has been developed based on a glassy carbon electrode modified with hybrid nanocomposites of cobalt phthalocyanine, graphene nanoplatelets, multi-walled carbon nanotubes and ionic liquids (IL). To improve the sensitivity and selectivity of the sensor, cobalt phthalocyanine (CoPc) was used as an effective redox mediator to promote and catalyze the artemisinin reduction. Furthermore, the graphene nanoplatelets and multi-walled carbon nanotubes were used as excellent conducting supporting materials to improve the sensitivity of the electrochemical sensor. Moreover, IL with a surface charge was also employed to prevent aggregation of the graphene nanoplatelets and multi-walled carbon nanotubes. The analytical signal was generated from the reduction of Co(III)Pc generated by artemisinin. The proposed electrochemical sensor was applied to the detection of artemisinin using differential pulse voltammetry and provided a signal with wide linearity ranging from 1.5-60 μM and 60-600 μM and a detection limit of 0.70 μM (3SD/m). Furthermore, the proposed sensor displayed good repeatability and reproducibility of 2.9-3.0 and 3.1-4.4% RSD, respectively. Applications of the sensor to drug and plant samples demonstrated accuracy in a range of 105-116% recoveries. In addition, the results were in good agreement with those obtained from the HPLC method as a reference technique. Thus, the proposed electrochemical sensor provides a new alternative platform for sensitive and selective determination of artemisinin in the analysis of pharmaceuticals with good precision and accuracy.

Analytical Methods for the Determination of Major Drugs Used for the Treatment of COVID-19. A Review

At the beginning of the COVID-19 outbreak (end 2019 - 2020), therapeutic treatments based on approved drugs have been the fastest approaches to combat the new coronavirus pandemic. Nowadays several vaccines are available. However, the worldwide vaccination program is going to take a long time and its success will depend on the vaccine public's acceptance. Therefore, outside of vaccination, the repurposing of existing antiviral, anti-inflammatory and other types of drugs, have been considered an alternative medical strategy for the COVI-19 infection. Due to the broad clinical potential of the drugs, but also to their possible side effects, analytical methods are needed to monitor the drug concentrations in biological fluids and pharmaceutical products. This review deals with analytical methods developed in the period 2015 - July 2021 to detect potential drugs that, according to a literature survey, have been taken into consideration for the treatment of COVID-19. The drugs considered here have been selected on the basis of the number of articles published in the period January 2020-July 2021, using the combination of the keywords: COVID-19 and drugs or SARS-CoV-2 and drugs. A section is also devoted to monoclonal antibodies. Over the period considered, the analytical methods have been employed in a variety of real samples, such as body fluids (plasma, blood and urine), pharmaceutical products, environmental matrices and food.

Capillary-based fluorescence microsensor with polyoxometalates as nanozyme for rapid and ultrasensitive detection of artemisinin

A novel capillary-based fluorescence microsensor for artemisinin was developed with functional polyoxometalates (POMs) as nanozyme by a layer-by-layer self-assembly strategy. Vanadomolybdophosphoric heteropoly acid (H₅PMo₁₀V₂O₄₀, PMoV₂) and tungstophosphoric heteropoly acid (Na₅PW₁₁O₃₉Cu, PW₁₁Cu) with high peroxidase-like activity were synthesized and immobilized on capillary to catalyze artemisinin/thiamine reaction and generate the amplified fluorescence signal. The wide linear range up to 13.0 μM with the low limit of detection of 0.03 μM (S/N = 3) was achieved for the determination of artemisinin by using the proposed POMs-microsensor. The method has been successfully used to detect artemisinin in human plasma and antimalarial drugs with satisfactory accuracy. This work developed a novel capillary fluorescence microsensor with functional POMs as nanozyme, which can serve as a promising candidate in fluorescence microanalysis.

Detection of ascorbic acid based on its quenching effect on luminol-artemisinin chemiluminescence

We find that luminol can react with artemisinin (ART) to produce chemiluminescence (CL) in the absence of a catalyst and ascorbic acid (AA) can quench luminol-ART CL. Based on its efficient inhibition effect on luminol-ART CL, a new AA detection method is established. The calibration curve for the determination of AA is in the linear range of 5 × 10^-7 M to 1 × 10^-4 M with a detection limit of 50 nM, which is more sensitive than many other reported methods. This CL approach was utilized to detect AA in vitamin C tablets by applying the standard addition method, and the recoveries of 104.0%, 96.8% and 103.4% were obtained, respectively, at concentrations of 1 μM, 5 μM and 10 μM with a RSD value of less than 3.6%. This developed method for AA assay is distinguished by its fastness, reproducibility, easy operation and good selectivity.

Electrochemical determination of artemisinin based on signal inhibition for the reduction of hemin

A novel electrochemical sensor was constructed for the determination of artemisinin (ART) based on the inhibition of redox for hemin caused by ART. As far as we know, this strategy for ART determination may be proposed for the first time. In this work, untreated multi-walled carbon nanotubes were cast on the glassy carbon electrode (GCE) as conductive carrier. We prepared a bimetallic organic framework named FeGd-MOF and combined it with hemin by a simple physical mixed method. Then, we fabricated the working electrode by layer-by-layer modification and immobilization. The sensor measured by the differential pulse voltammetry (DPV) technique had calibration curves for the determination of ART, which was 0.3-350 μM with the correlation coefficient R² = 0.9998. Furthermore, the obtained linear range could be practically used in real sample analysis such as dried leaves of Artemisia apiacea. Under the optimized condition, the electrochemical sensor exhibited high sensitivity, good stability, and excellent anti-interference performance. The limit of detection (LOD) for this sensor was 0.17 μM (signal to noise ratio, S/N = 3), which was much lower than that for some other reported electrochemical sensors. The recovery rates were in the range of 99.54-104.34% in real samples, indicating that the sensor had good repetition and high accuracy. Graphical abstract.

A novel and sensitive fluorescent assay for artemisinin with graphene quantum dots based on inner filter effect

The authors describe a novel method for the determination of artemisinin (ART) by using graphene quantum dots (GQDs) as the fluorescent probes. This method is based on the fact that ART can react with p-aminophenylboronic acid (p-ABA) to produce p-aminophenol (p-AP). While in the presence of tyrosinase (TYR), p-AP can be oxidized into 4-amino-1,2-benzoquinone, which effectively quenched the fluorescence of GQDs due to the inner filter effect (IFE). By making use of these reactions, a novel and sensitive fluorescent assay for ART has been developed. The calibration curve for the determination of ART is linear in the range of 0.1-5 μM and 5-55 μM with the detection limit of 33 nM, which is more sensitive than most of other methods. Some common coexisting substances including Ca²⁺, Na⁺, Mg²⁺, K⁺, PO₄^3-, starch, lactose, dextrin, and magnesium stearat have negligible effects on the fluorescence intensity of GQDs-TYR-p-ABA system. Finally, the sensing system was successfully applied to the detection of the compound naphthoquine phosphate tablet samples with satisfactory recoveries. This IFE-based GQDs fluorescence sensing strategy is facile and sensitive for the determination of ART because neither the surface modification nor the linking between the receptor and the fluorophore is required.