LISzyme Biosensors: DNAzymes Embedded in an Anti-biofouling Platform for Hands-free Real-Time Detection of Bacterial Contamination in Milk

Comprehensive fluorescence profiles of contamination-prone foods applied to the design of microcontact-printed in situ functional oligonucleotide sensors

With both foodborne illness and food spoilage detrimentally impacting human health and the economy, there is growing interest in the development of in situ sensors that offer real-time monitoring of food quality within enclosed food packages. While oligonucleotide-based fluorescent sensors have illustrated significant promise, the development of such on-food sensors requires consideration towards sensing-relevant fluorescence properties of target food products-information that has not yet been reported. To address this need, comprehensive fluorescence profiles for various contamination-prone food products are established in this study across several wavelengths and timepoints. The intensity of these food backgrounds is further contextualized to biomolecule-mediated sensing using overlaid fluorescent oligonucleotide arrays, which offer perspective towards the viability of distinct wavelengths and fluorophores for in situ food monitoring. Results show that biosensing in the Cyanine3 range is optimal for all tested foods, with the Cyanine5 range offering comparable performance with meat products specifically. Moreover, recognizing that mass fabrication of on-food sensors requires rapid and simple deposition of sensing agents onto packaging substrates, RNA-cleaving fluorescent nucleic acid probes are successfully deposited via microcontact printing for the first time. Direct incorporation onto food packaging yields cost-effective sensors with performance comparable to ones produced using conventional deposition strategies.

Material Breakthroughs in Smart Food Monitoring: Intelligent Packaging and On-Site Testing Technologies for Spoilage and Contamination Detection

Despite extensive commercial and regulatory interventions, food spoilage and contamination continue to impose massive ramifications on human health and the global economy. Recognizing that such issues will be significantly eliminated by the accurate and timely monitoring of food quality markers, smart food sensors have garnered significant interest as platforms for both real-time, in-package food monitoring and on-site commercial testing. In both cases, the sensitivity, stability, and efficiency of the developed sensors are largely informed by underlying material design, driving focus toward the creation of advanced materials optimized for such applications. Herein, a comprehensive review of emerging intelligent materials and sensors developed in this space is provided, through the lens of three key food quality markers - biogenic amines, pH, and pathogenic microbes. Each sensing platform is presented with targeted consideration toward the contributions of the underlying metallic or polymeric substrate to the sensing mechanism and detection performance. Further, the real-world applicability of presented works is considered with respect to their capabilities, regulatory adherence, and commercial potential. Finally, a situational assessment of the current state of intelligent food monitoring technologies is provided, discussing material-centric strategies to address their existing limitations, regulatory concerns, and commercial considerations.

Superomniphobic and Photoactive Surface Presents Antimicrobial Properties by Repelling and Killing Pathogens

Healthcare-acquired infections place a significant burden on the cost and quality of patient care in hospitals. Reducing contamination on surfaces within healthcare environments is critical for halting the spread of these infections. Herein, we report a bifunctional─repel and kill─surface developed using photoactive TiO2 nanoparticles integrated into a hierarchical scaffold (OmniKill). To quantify the repellency of OmniKill, we developed a touch-based assay, capable of simulating the transfer of individual pathogens, multiple pathogens, or pathogen-latent fecal matter from hands to surfaces. OmniKill repels bacterial pathogens by at least 2.77-log (99.8%). The photoactive material within OmniKill further reduces the viability of transferred pathogens on the surface by an additional 2.43-log (99.6%) after 1 h of light exposure. The antipathogenic effects─repel and kill─remain robust under complex biological contaminates such as feces. These findings show the potential use of OmniKill in reducing the physical transmission of bacterial pathogens in healthcare settings.

Synthesis of γ-Cyclodextrin-Reduced Fe(III) Nanoparticles with Peroxidase-like Catalytic Activity for Bacteriostasis of Food

Foodborne pathogens are a primary cause of human foodborne illness, making it imperative to explore novel antibacterial strategies for their control. In this study, Fe-γ-CD was successfully synthesized as a food antibacterial agent for use in milk and orange juice. The Fe-γ-CD consists of 6/11 Fe(II) and 5/11 Fe(III), which catalyze a Fenton-like catalytic reaction with H2O2 to generate •OH. Consequently, Fe-γ-CD exhibits exceptional peroxidase-like activity and broad-spectrum antibacterial efficacy. Fe-γ-CD not only disrupts the wall structure of ESBL-E. coli but also induces protein leakage and genetic destruction, ultimately leading to its death. Furthermore, Fe-γ-CD inhibits biofilm formation by MRSA and eradicates mature biofilms, resulting in MRSA's demise. Importantly, Fe-γ-CD demonstrates negligible cytotoxicity toward normal mammalian cells, making it an ideal candidate for application as an antibacterial agent in foodstuffs. These findings highlight that Fe-γ-CD is an effective tool for combating the spread of foodborne pathogens and food safety.

In Vitro Selection of M2+-Independent, Fast-Responding Acidic Deoxyribozymes for Bacterial Detection

We report on the first efforts to isolate acidic RNA-cleaving DNAzymes (aRCDs) from a random-sequence DNA pool by in vitro selection that are activated by a microbe Escherichia coli (E. coli), at pH 5.3. Importantly, these E. coli-responsive aRCDs only require monovalent metal ions as cofactors for cleaving a fluorogenic chimeric DNA/RNA substrate. Such characteristics can be used to efficiently protect RCDs from both intrinsic chemical instability and external enzymatic degradation. One remarkable DNAzyme, aRCD-EC1, is specific for E. coli, and its target is likely a protein. Furthermore, truncated aRCD-EC1 had significantly improved catalytic activity with an observed rate constant (kobs) of 1.18 min-1, making it the fastest bacteria-responding RCD reported to date. Clinical evaluation of this aRCD-based fluorescent assay using 40 patient urine samples demonstrated a diagnostic sensitivity of 100% and a specificity of 100% at a total analysis time of 50 min without a bacterial culture. This work can expand the repertoire of DNAzymes that are active under nonphysiological conditions, thus facilitating the development of diverse DNAzyme-based biosensors in clinical diagnosis.

Advancing In Situ Food Monitoring through a Smart Lab-in-a-Package System Demonstrated by the Detection of Salmonella in Whole Chicken

With food production shifting away from traditional farm-to-table approaches to efficient multistep supply chains, the incidence of food contamination has increased. Consequently, pathogen testing via inefficient culture-based methods has increased, despite its lack of real-time capabilities and need for centralized facilities. While in situ pathogen detection would address these limitations and enable individual product monitoring, accurate detection within unprocessed, packaged food products without user manipulation has proven elusive. Herein, "Lab-in-a-Package" is presented, a platform capable of sampling, concentrating, and detecting target pathogens within closed food packaging, without intervention. This system consists of a newly designed packaging tray and reagent-infused membrane that can be paired universally with diverse pathogen sensors. The inclined food packaging tray maximizes fluid localization onto the sensing interface, while the membrane acts as a reagent-immobilizing matrix and an antifouling barrier for the sensor. The platform is substantiated using a newly discovered Salmonella-responsive nucleic acid probe, which enables hands-free detection of 103 colony forming units (CFU) g-1 target pathogen in a packaged whole chicken. The platform remains effective when contamination is introduced with toolsand surfaces, ensuring widespread efficacy. Its real-world use for in situ detection is simulated using a handheld fluorescence scanner with smartphone connectivity.

An electrochemical biosensor for HER2 detection in complex biological media based on two antifouling materials of designed recognizing peptide and PEG

A simple tactic for electrochemical determination of a typical biomarker for breast cancer, human epidermal growth factor receptor 2 (HER2), was presented via the construction of a low fouling sensing interface functionalized with polyethylene glycol (PEG) and peptide. The HER2 biosensor was developed based on an electrode modified by the conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) and Au nanoparticles (AuNPs) as the sensing substrate, and followed by the immobilization of an antifouling PEG and a peptide with both recognizing and antifouling properties. Thanks to the combined antifouling effect of the PEG and peptide, and the specific recognizing ability of the peptide to the target HER2, the developed electrochemical biosensor exhibited strong antifouling performances in complex biofluids, such as human blood and serum, and it was capable of assaying target HER2 within a very wide linear range (1.0 pg mL^-1 to 1.0 μg mL^-1), with an ultralow limit of detection (0.44 pg mL^-1). The combination of two kinds of antifouling biomaterials (PEG and peptide) offered an effective strategy for the development of low fouling sensing platforms suitable for practical assay in complex biotic environments.

Liquid NanoBiosensors Enable One-Pot Electrochemical Detection of Bacteria in Complex Matrices

There is a need for point-of-care bacterial sensing and identification technologies that are rapid and simple to operate. Technologies that do not rely on growth cultures, nucleic acid amplification, step-wise reagent addition, and complex sample processing are the key for meeting this need. Herein, multiple materials technologies are integrated for overcoming the obstacles in creating rapid and one-pot bacterial sensing platforms. Liquid-infused nanoelectrodes are developed for reducing nonspecific binding on the transducer surface; bacterium-specific RNA-cleaving DNAzymes are used for bacterial identification; and redox DNA barcodes embedded into DNAzymes are used for binding-induced electrochemical signal transduction. The resultant single-step and one-pot assay demonstrates a limit-of-detection of 10² CFU mL^-1 , with high specificity in identifying Escherichia coli amongst other Gram positive and negative bacteria including Klebsiella pneumoniae, Staphylococcus aureus, and Bacillus subtilis. Additionally, this assay is evaluated for analyzing 31 clinically obtained urine samples, demonstrating a clinical sensitivity of 100% and specify of 100%. When challenging this assay with nine clinical blood cultures, E. coli-positive and E. coli-negative samples can be distinguished with a probability of p < 0.001.

Portable dual-aptamer microfluidic chip biosensor for Bacillus cereus based on aptamer tailoring and dumbbell-shaped probes

As food-borne pathogens, Bacillus cereus not only produce toxins that contaminate food and threaten human health, but also rely on spores to resist extreme environments. At present, the detection of B. cereus is still at the genome level and it is not easily distinguished from other Bacilli of the same group. Herein, we obtained the aptamers of B. cereus in different phases through Cell-SELEX technology. Then, through step-by-step tailoring and molecular docking, the two best performing aptamers were ascertained and the interaction revealed between the repeated G bases in the aptamer and the polar amino acids in the α-helix of the epiprotein. Based on these aptamers, a multifunctional dumbbell-shaped probe and an ultrasensitive microfluidic chip biosensor were designed. Tests showed that the novel sensor is able to complete detection within 1 h with a limit of detection (LOD) of 9.27 CFU/mL. Moreover, the sensor can be used in complex food environments, such as milk and rice, is able to detect both vegetative cells and spores, and it can also distinguish B. thuringiensis from the same flora. This study can provide a reference for the future development of food-borne pathogenic bacteria aptamer selecting, target interaction analysis, detection methods and equipment.

Highly Stable Hierarchically Structured All-Polymeric Lubricant-Infused Films Prevent Thrombosis and Repel Multidrug-Resistant Pathogens

Thrombus formation and infections caused by bacterial adhesion are the most common causes of failure in blood-contacting medical devices. Reducing the interaction of pathogens using repellent surfaces has proven to be a successful strategy in preventing device failure. However, designing scale-up methodologies to create large-scale repellent surfaces remains challenging. To address this need, we have created an all-polymeric lubricant-infused system using an industrially viable swelling-coagulation solvent (S-C) method. This induces hierarchically structured micro/nano features onto the surface, enabling improved lubricant infusion. Poly(3,3,3-trifluoropropylmethylsiloxane) (PTFS) was used as the lubricant of choice, a previously unexplored omniphobic nonvolatile silicone oil. This resulted in all-polymeric liquid-infused surfaces that are transparent and flexible with long-term stability. Repellent properties have been demonstrated using human whole blood and methicillin-resistant Staphylococcus aureus (MRSA) bacteria matrices, with lubricated surfaces showing 93% reduction in blood stains and 96.7% reduction in bacterial adherence. The developed material has the potential to prevent blood and pathogenic contamination for a range biomedical devices within healthcare settings.

Bioinspired liquid-infused surface for biomedical and biosensing applications

Nature always inspires us to develop advanced materials for diverse applications. The liquid-infused surface (LIS) inspired by Nepenthes pitcher plants has aroused broad interest in fabricating anti-biofouling materials over the past decade. The infused liquid layer on the solid substrate repels immiscible fluids and displays ultralow adhesion to various biomolecules. Due to these fascinating features, bioinspired LIS has been applied in biomedical-related fields. Here, we review the recent progress of LIS in bioengineering, medical devices, and biosensing, and highlight how the infused liquid layer affects the performance of medical materials. The prospects for the future trend of LIS are also presented.

Contamination and carryover free handling of complex fluids using lubricant-infused pipette tips

Cross-contamination of biological samples during handling and preparation, is a major issue in laboratory setups, leading to false-positives or false-negatives. Sample carryover residue in pipette tips contributes greatly to this issue. Most pipette tips on the market are manufactured with hydrophobic polymers that are able to repel high surface tension liquids, yet they lack in performance when low surface tension liquids and viscous fluids are involved. Moreover, hydrophobicity of pipette tips can result in hydrophobic adsorption of biomolecules, causing inaccuracies and loss in precision during pipetting. Here we propose the use of lubricant-infused surface (LIS) technology to achieve omniphobic properties in pipette tips. Using a versatile and simple design, the inner lumen of commercially available pipette tips was coated with a fluorosilane (FS) layer using chemical vapor deposition (CVD). The presence of FS groups on the tips is confirmed by x-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) tests. After lubrication of the tips through a fluorinated lubricant, the omniphobicity and repellent behaviour of the tips drastically enhanced which are revealed via static and hysteresis contact angle measurements. The repellency of the lubricant-infused pipette tips against physical adsorption is investigated through pipetting a food coloring dye as well as human blood samples and are compared to the untreated tips. The results show significantly less amount carryover residue when the lubricant-infused tips are utilized compared to commercially available ones. We also demonstrate the lubricant-infused tips reduce bacteria contamination of the inner lumen by 3 to 6-log (over 99%, depending on the tip size) after pipetting up and down the bacteria solution.

DNA-based enzymatic systems and their applications

DNA strands with unique secondary structures can catalyze various chemical reactions and mimic natural enzymes with the assistance of cofactors, which have attracted much research attention. At the same time, the emerging DNA nanotechnology provides an efficient platform to organize functional components of the enzymatic systems and regulate their catalytic performances. In this review, we summarize the recent progress of DNA-based enzymatic systems. First, DNAzymes (Dzs) are introduced, and their versatile utilities are summarized. Then, G-quadruplex/hemin (G4/hemin) Dzs with unique oxidase/peroxidase-mimicking activities and representative examples where these Dzs served as biosensors are explicitly elaborated. Next, the DNA-based enzymatic cascade systems fabricated by the structural DNA nanotechnology are depicted. In addition, the applications of catalytic DNA nanostructures in biosensing and biomedicine are included. At last, the challenges and the perspectives of the DNA-based enzymatic systems for practical applications are also discussed.

Enhancing osseointegration and mitigating bacterial biofilms on medical-grade titanium with chitosan-conjugated liquid-infused coatings

Titanium alloys, in particular, medical-grade Ti-6Al-4 V, are heavily used in orthopaedic applications due to their high moduli, strength, and biocompatibility. Implant infection can result in biofilm formation and failure of prosthesis. The formation of a biofilm on implants protects bacteria from antibiotics and the immune response, resulting in the propagation of the infection and ultimately resulting in device failure. Recently, slippery liquid-infused surfaces (LIS) have been investigated for their stable liquid interface, which provides excellent repellent properties to suppress biofilm formation. One of the current limitations of LIS coatings lies in the indistinctive repellency of bone cells in orthopaedic applications, resulting in poor tissue integration and bone ingrowth with the implant. Here, we report a chitosan impregnated LIS coating that facilitates cell adhesion while preventing biofilm formation. The fabricated coating displayed high contact angles (108.2 ± 5.2°) and low sliding angles (3.56 ± 4.3°). Elemental analysis obtained using X-ray photoelectron spectroscopy (XPS) confirmed the availability of fluorine and nitrogen, indicating the presence of fluorosilane and chitosan in the final coating. Furthermore, our results suggest that chitosan-conjugated LIS increased cell adhesion of osteoblast-like SaOS-2 cells and significantly promoted proliferation (a fourfold increase at 7-day incubation) compared to conventional titanium liquid-infused surfaces. Furthermore, the chitosan conjugated LIS significantly reduced biofilm formation of methicillin-resistant Staphylococcus aureus (MRSA) by up to 50% and 75% when compared to untreated titanium and chitosan-coated titanium, respectively. The engineered coating can be easily modified with other biopolymers or capture molecules to be applied to other biomaterials where tissue integration and biofilm prevention are needed.