Controlled molecular architectures in microfluidic immunosensors for detecting Staphylococcus aureus

Aptamer-modified paper-based analytical devices for the detection of food hazards: Emerging applications and future perspective

Food analysis plays a critical role in assessing human health risks and monitoring food quality and safety. Currently, there is a pressing need for a reliable, portable, and quick recognition element for point-of-care testing (POCT) to better serve the demands of on-site food analysis. Aptamer-modified paper-based analytical devices (Apt-PADs) have excellent characteristics of high portability, high sensitivity, high specificity, and on-site detection, which have been widely used and concerned in the field of food safety. The article reviews the basic components and working principles of Apt-PADs, and introduces their representative applications detecting food hazards. Finally, the advantages, challenges, and future directions of Apt-PADs-based sensing performance are discussed, to provide new directions and insights for researchers to select appropriate Apt-PADs according to specific applications.

Point-of-Care Electrochemical Immunosensor Applied against Nosocomial Infection: Staphylococcus aureus Detection in Human Hand Skin

Staphylococcus aureus is an important pathogen that causes nosocomial infections, resulting in unacceptable morbidity and mortality rates. In this work, we proposed the construction of a nanostructured ZnO-based electrochemical immunosensor for qualitative and semiquantitative detection of S. aureus using simple methods for growing zinc oxide nanorods (ZnO NRs) on a sensor board and immobilizing the anti-S. aureus antibody on ZnO NRs through cystamine and glutaraldehyde. The immunosensor detected S. aureus in the 103-107 colony-forming unit (CFU) mL-1 range and showed a limit of detection (LoD) around 0.792 × 103 CFU mL-1. Beyond a satisfactory LoD, the developed immunosensor presented other advantages, such as high versatility for point-of-care assays and a suitable selective factor that admits the detection of the S. aureus concentration range in human hand skin after washing. Moreover, the immunosensor showed the potential to be an excellent device to control nosocomial infection by detecting the presence of S. aureus in human hand skin.

Multidimensional calibration spaces in Staphylococcus Aureus detection using chitosan-based genosensors and electronic tongue

Mastitis diagnosis can be made by detecting Staphylococcus aureus (S. aureus), which requires high sensitivity and selectivity. Here, we report on microfluidic genosensors and electronic tongues to detect S. aureus DNA using impedance spectroscopy with data analysis employing visual analytics and machine learning techniques. The genosensors were made with layer-by-layer films containing either 10 bilayers of chitosan/chondroitin sulfate or 8 bilayers of chitosan/sericin functionalized with an active layer of cpDNA S. aureus. The specific interactions leading to hybridization in these genosensors allowed for a low limit of detection of 5.90 × 10-19 mol/L. The electronic tongue had four sensing units made with 6-bilayer chitosan/chondroitin sulfate films, 10-bilayer chitosan/chondroitin sulfate, 8-bilayer chitosan/sericin, and 8-bilayer chitosan/gold nanoparticles modified with sericin. Despite the absence of specific interactions, various concentrations of DNA S. aureus could be distinguished when the impedance data were plotted using a dimensionality reduction technique. Selectivity of S. aureus DNA was confirmed using multidimensional calibration spaces, based on machine learning, with accuracy up to 89 % for the genosensors and 66 % for the electronic tongue. Hence, with these computational methods one may opt for the more expensive genosensors or the simpler and cheaper electronic tongue, depending on the sensitivity level required to diagnose mastitis.

Vancomycin-modified nitrogen and chloride doped carbon dots and their application as a Staphylococcus aureus probe

In this research, N, Cl-doped carbon dots (N, Cl-CDs) were prepared in choline chloride-glycerol deep eutectic solvent (DES) by microwave method. N, Cl-CDs surface was modified with vancomycin for detection of Staphylococcus aureus (S. aureus) bacteria in the range of 10²-10⁷ colony-forming unit per milliliter (CFU/mL). The detection limit was 10¹ CFU/mL. Morphology and structure of N, Cl-CDs were characterized by transmission electron microscopy (TEM), X-ray photon spectroscopy (XPS), photoluminescence spectroscopy, FT-IR spectroscopy, energy dispersive X-ray spectroscopy (EDXS) and zeta potential. The prepared N, Cl-CDs had excellent dispersion in water, particle size range of 2-3 nm, and quantum yield of 38.75%. Speed, wide linear range and more convenient were advantages of new probe with respect to other methods.

Nanoarchitectonic E-Tongue of Electrospun Zein/Curcumin Carbon Dots for Detecting Staphylococcus aureusin Milk

We report a nanoarchitectonic electronic tongue made with flexible electrodes coated with curcumin carbon dots and zein electrospun nanofibers, which could detect Staphylococcus aureus(S. aureus) in milk using electrical impedance spectroscopy. Electronic tongues are based on the global selectivity concept in which the electrical responses of distinct sensing units are combined to provide a unique pattern, which in this case allowed the detection of S. aureus through non-specific interactions. The electronic tongue used here comprised 3 sensors with electrodes coated with zein nanofibers, carbon dots, and carbon dots with zein nanofibers. The capacitance data obtained with the three sensors were processed with a multidimensional projection technique referred to as interactive document mapping (IDMAP) and analyzed using the machine learning-based concept of multidimensional calibration space (MCS). The concentration of S. aureus could be determined with the sensing units, especially with the one containing zein as the limit of detection was 0.83 CFU/mL (CFU stands for colony-forming unit). This high sensitivity is attributed to molecular-level interactions between the protein zein and C-H groups in S. aureus according to polarization-modulated infrared reflection-absorption spectroscopy (PM-IRRAS) data. Using machine learning and IDMAP, we demonstrated the selectivity of the electronic tongue in distinguishing milk samples from mastitis-infected cows from milk collected from healthy cows, and from milk spiked with possible interferents. Calibration of the electronic tongue can also be reached with the MCS concept employing decision tree algorithms, with an 80.1% accuracy in the diagnosis of mastitis. The low-cost electronic tongue presented here may be exploited in diagnosing mastitis at early stages, with tests performed in the farms without requiring specialized laboratories or personnel.

Ag NP-filter paper based SERS sensor coupled with multivariate analysis for rapid identification of bacteria

Rapid and accurate identification of bacteria is essential to ensure food safety and prevent pathogenic bacterial infection. In this study, a highly efficient method was established for accurately identifying bacterial species by applying Ag NP-filter paper based Surface enhanced Raman spectroscopy (SERS) analysis and Partial Least Squares-Discriminant Analysis (PLS-DA) statistical methods. The flexible Ag NP filter paper substrate with high sensitivity and uniformity was prepared by a facile and low-cost silver mirror reaction at room temperature, which exhibited desirable SERS activity in bacteria detection. Furthermore, PLS-DA was successfully employed to distinguish SERS spectra from S. aureus CMCC 26003, E. faecalis ATCC29212 and L. monocytogenes ATCC 19115 with a sensitivity of 93.3-100%, specificity of 96.7-97%, and overall predicting accuracy of 95.8%. This exploratory study demonstrates that a Ag NP-filter paper based SERS sensor coupled with PLS-DA has great potential for rapid and effective detection and identification of bacteria.

An ultrasensitive fluorescence detection template of pathogenic bacteria based on dual catalytic hairpin DNA Walker@Gold nanoparticles enzyme-free amplification

Integrating the advantages of catalytic hairpin components and multi-foot DNA walker, we designed a 16S rRNA detection probe template for pathogen bacteria, which utilizes DNA ligation quencher and dual catalytic hairpin@DNA walker to induce signal recovery. The dual catalytic hairpin@DNA walker uses the walking position of the target on the AuNP as a foothold to promote the reaction, so that the biosensing of the low-abundance target sequence can induce signal recovery. During the entire experiment, no enzyme is required, which can avoid the limitation of enzyme degradation under unfavorable conditions and the inability to detect the target. Most importantly, the detection template has the advantages of high sensitivity, and its detection limit is significantly better than that of single hairpin DNA walker probe. As the detection system can sensitively and rapidly detect its targeted bacteria and not rely on any enzyme and sophisticated instrumentation, it has great potential for sensitive and specific pathogenic bacteria detection.

Diagnostics of SARS-CoV-2 infection using electrical impedance spectroscopy with an immunosensor to detect the spike protein

Mass testing for the diagnostics of COVID-19 has been hampered in many countries owing to the high cost of the methodologies to detect genetic material of SARS-CoV-2. In this paper, we report on a low-cost immunosensor capable of detecting the spike protein of SARS-CoV-2, including in samples of inactivated virus. Detection is performed with electrical impedance spectroscopy using an immunosensor that contains a monolayer film of carboxymethyl chitosan as matrix, coated with an active layer of antibodies specific to the spike protein. In addition to a low limit of detection of 0.179 fg/mL within an almost linear behavior from 10⁻²⁰ g/mL to 10⁻¹⁴ g/mL, the immunosensor was highly selective. For the samples with the spike protein could be distinguished in multidimensional projection plots from samples with other biomarkers and analytes that could be interfering species for healthy and infected patients. The excellent analytical performance of the immunosensors was validated with the distinction between control samples and those containing inactivated SARS-CoV-2 at different concentrations. The mechanism behind the immunosensor performance is the specific antibody-protein interaction, as confirmed with the changes induced in C–H stretching and protein bands in polarization-modulated infrared reflection absorption spectra (PM-IRRAS). Because impedance spectroscopy measurements can be made with low-cost portable instruments, the immunosensor proposed here can be applied in point-of-care diagnostics for mass testing even in places with limited resources.

Recent Advances in Microfluidic Devices for Contamination Detection and Quality Inspection of Milk

Milk is a necessity for human life. However, it is susceptible to contamination and adulteration. Microfluidic analysis devices have attracted significant attention for the high-throughput quality inspection and contaminant analysis of milk samples in recent years. This review describes the major proposals presented in the literature for the pretreatment, contaminant detection, and quality inspection of milk samples using microfluidic lab-on-a-chip and lab-on-paper platforms in the past five years. The review focuses on the sample separation, sample extraction, and sample preconcentration/amplification steps of the pretreatment process and the determination of aflatoxins, antibiotics, drugs, melamine, and foodborne pathogens in the detection process. Recent proposals for the general quality inspection of milk samples, including the viscosity and presence of adulteration, are also discussed. The review concludes with a brief perspective on the challenges facing the future development of microfluidic devices for the analysis of milk samples in the coming years.