Electrochemical methods for the determination of antibiotic residues in milk: A critical review

Several antibiotics have been applied to veterinary medicine due to their broad-spectrum of antibacterial activity and prophylactic power. Residues of these antibiotics can be accumulated in dairy cattle, in addition to promoting contamination of the environment and, in more serious cases, in milk, causing a public health problem. Different regulatory agencies establish maximum residue limits for these antibiotics in milk, so it becomes important to develop sensitive analytical methods for monitoring these compounds. Electrochemical techniques are important analytical tools in analytical chemistry because they present low cost, simplicity, high sensitivity, and adequate analytical frequency (sample throughput) for routine analyses. In this sense, this review summarizes the state of the art of the main electrochemical sensors and biosensors, instrumental techniques, and sample preparation used for the development of analytical methods, published in the last five years, for the monitoring of different classes of antibiotics: aminoglycosides, amphenicols, beta-lactams, fluoroquinolones, sulfonamides, and tetracyclines, in milk samples. The different strategies to develop electrochemical sensors and biosensors are critically compared considering their analytical features. The mechanisms of electrochemical oxidation/reduction of the antibiotics are revised and discussed considering strategies to improve the selectivity of the method. In addition, current challenges and future prospects are discussed.

A novel electrochemical aptasensor for the sensitive detection of kanamycin based on UiO-66-NH2/MCA/MWCNT@rGONR nanocomposites

In this work, we designed and synthesized a nanocomposite comprising an amine-functionalized metal organic framework (UiO-66-NH₂), a multiwalled carbon nanotube@reduced graphene oxide nanoribbon (MWCNT@rGONR) and a covalent organic framework (COF) synthesized using melamine and cyanuric acidmonomers via polycondensation (represented by MCA). The UiO-66-NH₂/MCA/MWCNT@rGONR nanocomposite was used as a sensitive platform for an electrochemical aptasensor to detect kanamycin (kana). Owing to the rich chemical functionality, amino-rich structure and excellent electrochemical activity, the cDNA strands with terminal amino groups can not only anchor over the UiO-66-NH₂/MCA/MWCNT@rGONR surface but also penetrate into the interior of porous UiO-66-NH₂/MCA/MWCNT@rGONR networks. The characterization of the UiO-66-NH₂/MCA/MWCNT@rGONR nanocomposite was performed by scanning electronic microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR) spectroscopy and X-ray diffraction (XRD). Furthermore, cyclic voltammetry (CV) and square wave voltammetry (SWV) were employed for the electrochemical performance study of this biosensor. The results indicated that the UiO-66-NH₂/MCA/MWCNT@rGONR nanocomposite exhibited high bioaffinity toward the aptamer and the lowest limit of detection at 13 nM (S/N = 3) within a linearity of the kana concentration of 25-900 nM. In addition, it possessed great repeatability, stability and selectivity and obtained satisfactory recovery results in the real analysis of fish meat and milk, indicating the great potential for analytical measurements in food safety.

Two kanamycin electrochemical aptamer-based sensors using different signal transduction mechanisms: A comparison of electrochemical behavior and sensing performance

Two typical kanamycin-A (KAN-A) electrochemical aptamer-based sensors employing different signal transduction mechanisms were deliberately designed and constructed with a similar structure. One sensor (sensor-1) was based on the classical probe conformation changing mode (PCCM) with a methylene blue (MB) label used as an electrochemical tag; the other sensor (sensor-2) used the target-induced signal probe shifting (TISPS) method with a free MB label in the assay solution. The difference in signal transduction mechanisms resulted in big differences in basic electrochemical behavior and comprehensive sensing performance. The results show that both sensor types exhibit different electrochemical behavior in square wave voltammetry, cyclic voltammetry, and in sensitivity, with detection limits of 3.0 nM for sensor-1 and 60.0 pM for sensor-2 in buffer. When validated for practical and quantitative detection of tap water and milk samples, both sensing methods performed well with detection limits of <260 nM and measurement times of <40 min. In addition, accuracy was good with mean recoveries of 72.3-92.6% and precision was acceptable with a relative standard deviation (RSD) of ≤14.2%. The basis for the similarities and differences in performance is also presented.

Smartphone-based kanamycin sensing with ratiometric FRET

Smartphone-based fluorescence detection is a promising avenue for biosensing that can aid on-site analysis. However, quantitative detection with fluorescence in the field has been limited due to challenges with robust excitation and calibration requirements. Here, we show that ratiometric analysis with Förster resonance energy transfer (FRET) between dye pairs on DNA aptamers can enable rapid and sensitive kanamycin detection. Since our detection scheme relies on ligand binding-induced changes in the aptamer tertiary structure, it is limited only by the kinetics of ligand binding to the aptamer. Our FRET-based kanamycin binding aptamer (KBA) sensor displays two linear ranges of 0.05-5 nM (detection limit of 0.18 nM) and 50-900 nM of kanamycin. The aptamer displays high specificity even in the presence of the 'natural' background from milk. By immobilizing the aptamer in the flow cell, our KBA sensor design is also suitable for repeated kanamycin detection. Finally, we show that the ratiometric FRET-based analysis can be implemented on a cheap custom-built smartphone setup. This smartphone-based FRET aptamer scheme detects kanamycin in a linear range of 50-500 nM with a limit of detection (LOD) of 28 nM.

Voltammetric kanamycin aptasensor based on the use of thionine incorporated into Au@Pt core-shell nanoparticles

A signal-on aptasensor is described for the voltammetric determination of kanamycin (KANA). Au@Pt core-shell nanoparticles with large surface and good electrical conductivity were synthetized and act as both a conductive material and as the carrier for complementary strands (CS2) and thionine (TH). In the presence of KANA, the electrochemical response of TH changes due to hybridization between CS1 immobilized on the electrode and the Au@Pt-CS2/TH system. The peak current increases linearly with the logarithm of the KANA concentration in the range from 1 pM to 1 μM, and the limit of detection is 0.16 pM. The sensor was characterized in terms of selectivity, reproducibility and stability, and satisfactory results were obtained. It was also utilized for the determination of KANA in (spiked) chicken samples. The recoveries (95.8-103.2%) demonstrate the potential of the method for KANA detection in real samples. Graphical abstract A signal-on aptasensor for kanamycin (KANA) was developed by using Au@Pt core-shell nanoparticles as nanocarrier for probe aptamer and as a sensing probe.

A label-free, versatile and low-background chemiluminescence aptasensing strategy based on gold nanocluster catalysis combined with the separation of magnetic beads

A label-free, versatile and low-background chemiluminescence sensing strategy based on gold nanocluster catalysis combined with magnetic separation was developed.