Ultrasensitive Detection of Staphylococcus aureus and Listeria monocytogenes Genomic DNA by Nanoparticle-Enhanced Surface Plasmon Resonance Imaging

Naked-eye detection of Staphylococcus aureus in powdered milk and infant formula using gold nanoparticles

Nonspecific binding of proteins from complex food matrices is a significant challenge associated with a biosensor using gold nanoparticles (AuNPs). To overcome this, we developed an efficient EDTA chelating treatment to denature milk proteins and prevent their adsorption on AuNPs. The use of EDTA to solubilize proteins enabled a sensitive label-free apta-sensor platform for colorimetric detection of Staphylococcus aureus in milk and infant formula. In the assay, S. aureus depleted aptamers from the test solution, and the reduction of aptamers enabled aggregation of AuNPs upon salt addition, a process characterized by a color change from red to purple. Under optimized conditions, S. aureus could be visually detected within 30 min with the detection limit of 7.5 × 10⁴ CFU/mL and 8.4 × 10⁴ CFU/mL in milk and infant formula, respectively. The EDTA treatment provides new opportunities for monitoring milk contamination and may prove valuable for biosensor point-of-need applications.

Nanoparticle-Enhanced Surface Plasmon Resonance Imaging Enables the Ultrasensitive Detection of Non-Amplified Cell-Free Fetal DNA for Non-Invasive Prenatal Testing

Although many potential applications in early clinical diagnosis have been proposed, the use of a surface plasmon resonance imaging (SPRI) technique for non-invasive prenatal diagnostic approaches based on maternal blood analysis is confined. Here, we report a nanoparticle-enhanced SPRI strategy for a non-invasive prenatal fetal sex determination based on the detection of a Y-chromosome specific sequence (single-gene SRY) in cell-free fetal DNA from maternal plasma. The SPR assay proposed here allows for detection of male DNA in mixtures of 2.5 aM male and female genomic DNAs with no preliminary amplification of the DNA target sequence, thus establishing an analytical protocol that does not require costly, time-consuming, and prone to sample contamination PCR-based procedures. Afterward, the developed protocol was successfully applied to reveal male cell-free fetal DNA in the plasma of pregnant women at different gestational ages, including early gestational ages. This approach would pave the way for the establishment of faster and cost-effective non-invasive prenatal testing.

Influence of citrate buffer and flash heating in enhancing the sensitivity of ratiometric genosensing of Hepatitis C virus using plasmonic gold nanoparticles

Gold nanoparticles (Au NPs) based technology has been shown to possess enormous potential in the viral nucleic acid diagnosis. Despite significant advancement in this domain, the existing literature reveals the diversity in the conditions employed for hybridization and tagging of thiolated nucleic acid probes over the Au NPs. Here we employ the probe sequence derived from the Hepatitis C virus to identify the optimal hybridization and thiol-Au NP tagging conditions. In a typical polymerase chain reaction, the probes are initially subjected to flash heating at elevated temperatures to obtain efficient annealing. Motivated by this, in the current study, the hybridization between the target and the antisense oligonucleotide (ASO) has been studied at 65 °C with and without employing flash heating at temperatures from 75 to 95 °C. Besides, the efficiency of the thiolated ASO’s tagging over the Au NPs with and without citrate buffer has been explored. The study has revealed the beneficial role of flash heating at 95 °C for efficient hybridization and the presence of citrate buffer for rapid and effective thiol tagging over the Au NPs. The combinatorial effect of these conditions has been found to be advantageous in enhancing the sensitivity of ratiometric genosensing using Au NPs.

Recent advances in Surface Plasmon Resonance (SPR) biosensors for food analysis: a review

Food safety is the prime area of concern that builds trust. With the prevailing advancements, it has become facile to ensure safety in almost all aspects. Technology has grown from tedious lab techniques to modern chromatographic techniques and immunoassays, progressed with more precise and rapid sensing through the advent of Biosensors. Biosensors provide an automated technology by presenting superfast, nondestructive and cost-effective detection in food analysis. SPR biosensor is an optical biosensor known for its versatility and has wider applications in food testing and analysis. It has an optical system for excitation and interrogation of surface plasmons, and a biomolecular recognition element to detect and seize the target analyte present in a sample. The optical signal detects the binding analyte, on the recognition element, which results in a change in refractive index at the surface and modifies the surface plasmons' propagation constant. SPR aids in label-free detection of various components such as adulterants, antibiotics, biomolecules, genetically modified foods, pesticides, insecticides, herbicides, microorganisms and microbial toxins in food and assures safety. The distinct advancements of SPR in food analysis have been found and discussed. The review also provides knowledge on the advantages and the key challenges encountered by SPR.

Recent Advances in Antifouling Materials for Surface Plasmon Resonance Biosensing in Clinical Diagnostics and Food Safety

Strategies to develop antifouling surface coatings are crucial for surface plasmon resonance (SPR) sensing in many analytical application fields, such as detecting human disease biomarkers for clinical diagnostics and monitoring foodborne pathogens and toxins involved in food quality control. In this review, firstly, we provide a brief discussion with considerations about the importance of adopting appropriate antifouling materials for achieving excellent performances in biosensing for food safety and clinical diagnosis. Secondly, a non-exhaustive landscape of polymeric layers is given in the context of surface modification and the mechanism of fouling resistance. Finally, we present an overview of some selected developments in SPR sensing, emphasizing applications of antifouling materials and progress to overcome the challenges related to the detection of targets in complex matrices relevant for diagnosis and food biosensing.

A fluorescent aptasensor for Staphylococcus aureus based on strand displacement amplification and self-assembled DNA hexagonal structure

A fluorescent aptasensor for Staphylococcus aureus (S. aureus) is designed, which takes advantage of strand displacement amplification (SDA) technology and unique self-assembled DNA hexagonal structure. In the presence of S. aureus, a partially complementary strand of S. aureus aptamer (cDNA) is competitively released from cDNA/aptamer duplex immobilized on magnetic beads due to the affinity of the aptamer for S. aureus. The addition of primer starts the SDA reaction. With the catalysis of Bsm DNA polymerase and Nb.bpu10I endonuclease, a large number of single-stranded DNA (ssDNA) is produced, which induces the opening of a hairpin probe and the subsequent self-assembly to form a hexagonal structure. The staining of the DNA hexagon with SYBR Green I excites the fluorescence signal, which is used for detection. The aptasensor exhibits a broad linear range from 7 to 7 × 10⁷ CFU/mL, with a detection limit of 1.7 CFU/mL for S. aureus. The sensor shows negligible responses to other bacteria. Moreover, the aptasensor has been applied to detect S. aureus in milk samples, and the results demonstrate the general applicability of the sensor and its prospect in systematic detection of S. aureus in food safety control and medicine-related fields. Graphical abstract The presence of S. aureus can be converted to the formation of unique DNA hexagonal structure and subsequent fluorescent signal by the combination of SDA with self-assembly technology.

Surface Plasmon Resonance for Biomarker Detection: Advances in Non-invasive Cancer Diagnosis

Biomarker-based cancer analysis has great potential to lead to a better understanding of disease at the molecular level and to improve early diagnosis and monitoring. Unlike conventional tissue biopsy, liquid biopsy allows the detection of a large variety of circulating biomarkers, such as microRNA (miRNA), exosomes, circulating tumor DNA (ctDNA), circulating tumor cells (CTCs), and proteins, in an easily accessible and minimally invasive way. In this review, we describe and evaluate the relevance and applicability of surface plasmon resonance (SPR) and localized SPR (LSPR)-based platforms for the detection of different classes of cancer biomarkers in liquid biopsy samples. Firstly, we critically discuss unsolved problems and issues in capturing and analyzing biomarkers. Secondly, we highlight current challenges which need to be resolved in applying SPR biosensors into clinical practice. Then, we mainly focus on applications of SPR-based platforms that process a patient sample aiming to detect and quantify biomarkers as a minimally invasive liquid biopsy tool for cancer patients appearing over the last 5 years. Finally, we describe the analytical performances of selected SPR biosensor assays and their significant advantages in terms of high sensitivity and specificity as well as accuracy and workflow simplicity.

Point-of-Need DNA Testing for Detection of Foodborne Pathogenic Bacteria

Foodborne pathogenic bacteria present a crucial food safety issue. Conventional diagnostic methods are time-consuming and can be only performed on previously produced food. The advancing field of point-of-need diagnostic devices integrating molecular methods, biosensors, microfluidics, and nanomaterials offers new avenues for swift, low-cost detection of pathogens with high sensitivity and specificity. These analyses and screening of food items can be performed during all phases of production. This review presents major developments achieved in recent years in point-of-need diagnostics in land-based sector and sheds light on current challenges in achieving wider acceptance of portable devices in the food industry. Particular emphasis is placed on methods for testing nucleic acids, protocols for portable nucleic acid extraction and amplification, as well as on the means for low-cost detection and read-out signal amplification.