Portable paper-based colorimetric nanoprobe for the detection of Stachybotrys chartarum using peptide labeled magnetic nanoparticles

Magnetic Nanobead Paper-Based Biosensors for Colorimetric Detection of Candida albicans

Candida albicans (C. albicans) infections pose significant challenges in clinical settings due to their high morbidity and mortality rates in addition to their role in tumor progression. Current diagnostic methods, while effective, often suffer from limitations that hinder a timely intervention. Therefore, there is an urgent need for a simple, sensitive, specific, and low-cost colorimetric biosensor for the rapid detection of C. albicans. This new biosensing platform comprises a gold platform carrying a specific C. albicans peptide substrate conjugated with magnetic nanobeads. Hence, the sensing platform was black, and the operation was based on the proteolytic activity of C. albicans, offering a visual color change to yellow upon cleavage of the conjugated peptide substrates on the magnetic nanobeads. Specificity testing demonstrated the biosensor's ability to distinguish C. albicans from other Candida species and microorganisms, while stability testing confirmed its long-term performance. Clinical testing revealed the biosensor's high sensitivity in detecting C. albicans in both standard cultures and clinically isolated samples with a lower limit of detestation of 3.5 × 103 CFU/mL. Although further validation against conventional and molecular methods is warranted, our colorimetric biosensor holds promise as a rapid (5 min) and cheap (Less than 2 $) point-of-care solution for the early detection of C. albicans infections, facilitating a timely intervention and improving patient outcomes in clinical practice.

Digitalization of Colorimetric Sensor Technologies for Food Safety

Colorimetric sensors play a crucial role in promoting on-site testing, enabling the detection and/or quantification of various analytes based on changes in color. These sensors offer several advantages, such as simplicity, cost-effectiveness, and visual readouts, making them suitable for a wide range of applications, including food safety and monitoring. A critical component in portable colorimetric sensors involves their integration with color models for effective analysis and interpretation of output signals. The most commonly used models include CIELAB (Commission Internationale de l'Eclairage), RGB (Red, Green, Blue), and HSV (Hue, Saturation, Value). This review outlines the use of color models via digitalization in sensing applications within the food safety and monitoring field. Additionally, challenges, future directions, and considerations are discussed, highlighting a significant gap in integrating a comparative analysis toward determining the color model that results in the highest sensor performance. The aim of this review is to underline the potential of this integration in mitigating the global impact of food spoilage and contamination on health and the economy, proposing a multidisciplinary approach to harness the full capabilities of colorimetric sensors in ensuring food safety.

Paper-based sensors: affordable, versatile, and emerging analyte detection platforms

Paper-based sensors, often referred to as paper-based analytical devices (PADs), stand as a transformative technology in the field of analytical chemistry. They offer an affordable, versatile, and accessible solution for diverse analyte detection. These sensors harness the unique properties of paper substrates to provide a cost-effective and adaptable platform for rapid analyte detection, spanning chemical species, biomolecules, and pathogens. This review highlights the key attributes that make paper-based sensors an attractive choice for analyte detection. PADs demonstrate their versatility by accommodating a wide range of analytes, from ions and gases to proteins, nucleic acids, and more, with customizable designs for specific applications. Their user-friendly operation and minimal infrastructure requirements suit point-of-care diagnostics, environmental monitoring, food safety, and more. This review also explores various fabrication methods such as inkjet printing, wax printing, screen printing, dip coating, and photolithography. Incorporating nanomaterials and biorecognition elements promises even more sophisticated and sensitive applications.

Microfluidics in environmental analysis: advancements, challenges, and future prospects for rapid and efficient monitoring

Microfluidic devices have emerged as advantageous tools for detecting environmental contaminants due to their portability, ease of use, cost-effectiveness, and rapid response capabilities. These devices have wide-ranging applications in environmental monitoring of air, water, and soil matrices, and have also been applied to agricultural monitoring. Although several previous reviews have explored microfluidic devices' utility, this paper presents an up-to-date account of the latest advancements in this field for environmental monitoring, looking back at the past five years. In this review, we discuss devices for prominent contaminants such as heavy metals, pesticides, nutrients, microorganisms, per- and polyfluoroalkyl substances (PFAS), etc. We cover numerous detection methods (electrochemical, colorimetric, fluorescent, etc.) and critically assess the current state of microfluidic devices for environmental monitoring, highlighting both their successes and limitations. Moreover, we propose potential strategies to mitigate these limitations and offer valuable insights into future research and development directions.

Microfluidics: a concise review of the history, principles, design, applications, and future outlook

Microfluidic technologies have garnered significant attention due to their ability to rapidly process samples and precisely manipulate fluids in assays, making them an attractive alternative to conventional experimental methods. With the potential for revolutionary capabilities in the future, this concise review provides readers with insights into the fascinating world of microfluidics. It begins by introducing the subject's historical background, allowing readers to familiarize themselves with the basics. The review then delves into the fundamental principles, discussing the underlying phenomena at play. Additionally, it highlights the different aspects of microfluidic device design, classification, and fabrication. Furthermore, the paper explores various applications, the global market, recent advancements, and challenges in the field. Finally, the review presents a positive outlook on trends and draws lessons to support the future flourishing of microfluidic technologies.

A Portable Nanoprobe for Rapid and Sensitive Detection of SARS-CoV-2 S1 Protein

Simple, timely, and precise detection of SARS-CoV-2 in clinical samples and contaminated surfaces aids in lowering attendant morbidity/mortality related to this infectious virus. Currently applied diagnostic techniques depend on a timely laboratory report following PCR testing. However, the application of these tests is associated with inherent shortcomings due to the need for trained personnel, long-time centralized laboratories, and expensive instruments. Therefore, there is an interest in developing biosensing diagnostic frontiers that can help in eliminating these shortcomings with a relatively economical, easy-to-use, well-timed, precise and sensitive technology. This study reports the development of fabricated Q-tips designed to qualitatively and semi-quantitatively detect SARS-CoV-2 in clinical samples and contaminated non-absorbable surfaces. This colorimetric sensor is engineered to sandwich SARS-CoV-2 spike protein between the lactoferrin general capturing agent and the complementary ACE2-labeled receptor. The ACE2 receptor is decorated with an orange-colored polymeric nanoparticle to generate an optical visual signal upon pairing with the SARS-CoV-2 spike protein. This colorimetric change of the Q-tip testing zone from white to orange confirms a positive result. The visual detection limit of the COVID-19 engineered colorimetric Q-tip sensor was 100 pfu/mL within a relatively short turnaround time of 5 min. The linear working range of quantitation was 10³-10⁸ pfu/mL. The engineered sensor selectively targeted SARS-CoV-2 spike protein and did not bind to another coronavirus such as MERS-CoV, Flu A, or Flu B present on the contaminated surface. This novel detection tool is relatively cheap to produce and suitable for onsite detection of COVID-19 infection.

Simple and rapid peptide nanoprobe biosensor for the detection of Legionellaceae

This study demonstrates the development of a sensitive, specific, and quantitative peptide-based nanoprobe prototype assay for the detection of Legionellaceae in a simple way and in a short time. In this work, proteases present in the culture supernatants of Legionella spp. were used as a biomarker. Fluorogenic peptide substrates, specific to Legionella strains culture supernatant proteases, were identified. Peptidases produced a significant increase in the fluorescence intensity following the cleavage of the dipeptide fluorogenic substrates. The specific substrates were identified and coupled with carboxyl-terminated nano-magnetic particles (NMPs). On the other hand, the C-terminal was conjugated with the cysteine residue to covalently integrate with a gold sensing platform via the Au-S linkage. Four different sensors were fabricated from the four specific substrates, which were treated with the protesase of six different species of Legionella. In the presence of specific protease, the peptide sequence is digested and the magnetic nanobeads moved out of the gold surface, resulting in the apparence of gold color. One of the nanoprobes sensitivity detects as low as 60 CFU mL^-1 of Legionella anisa, Legionella micdadei, and Fluoribacter dumoffii. The cross-reactivity of the sensors was tested using other closely associated bacterial species and no significant cross-reactivity of the sensors was found. It is envisaged that this assay could be useful for screening purposes or might be supportive for the fast and easy detection of Legionella protease activity for water monitoring purposes.

Low-cost colorimetric diagnostic screening assay for methicillin resistant Staphylococcus aureus

The timely diagnosis of MRSA in clinical samples helps to reduce the attendant morbidity/mortality associated with infection due to the organism. The early institution of appropriate therapy or deployment of infection control protocols are dependent on a timely report from the microbiology laboratory. Various assays currently used in the identification of MRSA are associated with inherent shortcomings, thus there is a need to explore newer diagnostic frontiers that can eliminate some of these short comings at a relatively cheap, timely, specific and sensitive manner. We present in this study a MRSA specific optical immunosensor to detect the presence of the pathogen on contaminated surface using control and patient strains. Results revealed a detection limits of 10³ CFU mL-1 upon visual observation, and 29 CFU mL-1 as determined by the linear regression equation, following the use of ImageJ to quantify activated cotton swab color intensity. The specificity of the sensor was examined by blind testing a panel of non-MRSA bacteria (E. coli, S. aureus and S. epidermis). Negative visual read-out was observed for all tested non-specific bacteria except for MRSA. Assay takes an average of 5 min and presents a powerful point-of-care diagnostic platform for the detection of MRSA.

Aptasensor for the detection of Methicillin resistant Staphylococcus aureus on contaminated surfaces

There is mounting evidence that contaminated hospital environment plays a crucial role in the transmission of nosocomial pathogens such as MRSA. The institution of infection control protocols is predicated on the early laboratory detection of the pathogen from relevant samples. Processing of environmental samples for the presence of bacterial contaminants in the clinical environment is poorly standardized when compared with analysis of clinical samples. The various laboratory methods available for processing environmental samples are difficult to standardized and most require a long turnaround time before results are available. In this study, we present a report of the performance of a novel pathogen aptasensor swab designed to qualitatively and quantitatively detect MRSA, on contaminated non-absorbable surfaces. The visual detection limit of the MRSA aptasensor swab was less than 100 CFU/ml and theoretically using a standard curve, was 2 CFU/ml. A relatively short turnaround time of 5 min was established for the assay while the linear range of quantitation was 10²-10⁵ CFU/ml. Engineered aptasensor targets MRSA selectively and binds to none of the other tested bacterial pathogen, on a multi-contaminated surface. This novel detection tool was easy to use and relatively cheap to produce.

Rapid Colorimetric Detection of Pseudomonas aeruginosa in Clinical Isolates Using a Magnetic Nanoparticle Biosensor

A rapid, sensitive, and specific colorimetric biosensor based on the use of magnetic nanoparticles (MNPs) was designed for the detection of Pseudomonas aeruginosa in clinical samples. The biosensing platform was based on the measurement of P. aeruginosa proteolytic activity using a specific protease substrate. At the N-terminus, this substrate was covalently bound to MNPs and was linked to a gold sensor surface via cystine at the C-terminus of the substrates. The golden sensor appears black to naked eyes because of the coverage of the MNPs. However, upon proteolysis, the cleaved peptide-MNP moieties will be attracted by an external magnet, revealing the golden color of the sensor surface, which can be observed by the naked eye. In vitro, the biosensor was able to detect specifically and quantitatively the presence of P. aeruginosa with a detection limit of 10² cfu/mL in less than 1 min. The colorimetric biosensor was used to test its ability to detect in situ P. aeruginosa in clinical isolates from patients. This biochip is anticipated to be useful as a rapid point-of-care device for the diagnosis of P. aeruginosa-related infections.

The Efficiency of Color Space Channels to Quantify Color and Color Intensity Change in Liquids, pH Strips, and Lateral Flow Assays with Smartphones

Bottom-up, end-user based feed, and food analysis through smartphone quantification of lateral flow assays (LFA) has the potential to cause a paradigm shift in testing capabilities. However, most developed devices do not test the presence of and implications of inter-phone variation. Much discussion remains regarding optimum color space for smartphone colorimetric analyses and, an in-depth comparison of color space performance is missing. Moreover, a light-shielding box is often used to avoid variations caused by background illumination while the use of such a bulky add-on may be avoidable through image background correction. Here, quantification performance of individual channels of RGB, HSV, and LAB color space and ΔRGB was determined for color and color intensity variation using pH strips, filter paper with dropped nanoparticles, and colored solutions. LAB and HSV color space channels never outperformed the best RGB channels in any test. Background correction avoided measurement variation if no direct sunlight was used and functioned more efficiently outside a light-shielding box (prediction errors < 5%/35% for color/color intensity change). The system was validated using various phones for quantification of major allergens (i.e., gluten in buffer, bovine milk in goat milk and goat cheese), and, pH in soil extracts with commercial pH strips and LFA. Inter-phone variation was significant for LFA quantification but low using pH strips (prediction errors < 10% for all six phones compared). Thus, assays based on color change hold the strongest promise for end-user adapted smartphone diagnostics.