Authors: Cheng Peng, Y Sungtaek Ju

Portable microfluidic devices are promising for point-of-care (POC) diagnosis and bio- and environmental surveillance in resource-constrained or non-laboratory environments. Lateral-flow devices, some built off paper or strings, have been widely developed but the fixed layouts of their underlying wicking/microchannel structures limit their flexibility and present challenges in implementing multistep reactions. Digital microfluidics can circumvent these difficulties by addressing discrete droplets individually. Existing approaches to digital microfluidics, however, often require bulky power supplies/batteries and high voltage circuits. We present a scheme to drive digital microfluidic devices by converting mechanical energy of human fingers to electrical energy using an array of piezoelectric elements. We describe the integration our scheme into two promising digital microfluidics platforms: one based on the electro-wetting-on-dielectric (EWOD) phenomenon and the other on the electrophoretic control of droplet (EPD). Basic operations of droplet manipulations, such as droplet transport, merging and splitting, are demonstrated using the finger-powered digital-microfluidics.

Topics: Colorimetry; Electrochemical Techniques; Enzyme-Linked Immunosorbent Assay; Equipment Design; Fingers; Humans; Microfluidic Analytical Techniques; Microfluidics

PubMed: 28299696
DOI: 10.1007/978-1-4939-6911-1_20

Review

Authors: Zihan Gao, Yin Wang, Haijian Wang...

Cd, a major environmental pollutant, is heavily toxic to human health. Many traditional techniques are high-cost and complicated; thus, developing a simple, sensitive, convenient, and cheap monitoring approach is necessary. The aptamer can be obtained from a novel method called SELEX, which is widely used as a DNA biosensor for its easy acquisition and high affinity of the target, especially for heavy metal ions detection, such as Cd. In recent years, highly stable Cd aptamer oligonucleotides (CAOs) were observed, and electrochemical, fluorescent, and colorimetric biosensors based on aptamers have been designed to monitor Cd. In addition, the monitoring sensitivity of aptamer-based biosensors is improved with signal amplification mechanisms such as hybridization chain reactions and enzyme-free methods. This paper reviews approaches to building biosensors for inspecting Cd by electrochemical, fluorescent, and colorimetric methods. Finally, many practical applications of sensors and their implications for humans and the environment are discussed.

Topics: Humans; Aptamers, Nucleotide; Cadmium; Biosensing Techniques; Colorimetry; Environmental Pollutants

PubMed: 37366977
DOI: 10.3390/bios13060612

Review

Authors: A C Evans, N N Thadani, J Suh...

Biocomputing nanoplatforms are designed to detect and integrate single or multiple inputs under defined algorithms, such as Boolean logic gates, and generate functionally useful outputs, such as delivery of therapeutics or release of optically detectable signals. Using sensing modules composed of small molecules, polymers, nucleic acids, or proteins/peptides, nanoplatforms have been programmed to detect and process extrinsic stimuli, such as magnetic fields or light, or intrinsic stimuli, such as nucleic acids, enzymes, or pH. Stimulus detection can be transduced by the nanomaterial via three different mechanisms: system assembly, system disassembly, or system transformation. The increasingly sophisticated suite of biocomputing nanoplatforms may be invaluable for a multitude of applications, including medical diagnostics, biomedical imaging, environmental monitoring, and delivery of therapeutics to target cell populations.

Topics: Animals; Colorimetry; Computers, Molecular; Diagnostic Imaging; Drug Delivery Systems; Humans; Molecular Imaging; Nanoparticles; Nanotechnology

PubMed: 26826305
DOI: 10.1016/j.jconrel.2016.01.045

Review

Authors: Hee-Jae Jeon, Hyung Shik Kim, Euiheon Chung...

Diabetes mellitus accompanies an abnormally high glucose level in the bloodstream. Early diagnosis and proper glycemic management of blood glucose are essential to prevent further progression and complications. Biosensor-based colorimetric detection has progressed and shown potential in portable and inexpensive daily assessment of glucose levels because of its simplicity, low-cost, and convenient operation without sophisticated instrumentation. Colorimetric glucose biosensors commonly use natural enzymes that recognize glucose and chromophores that detect enzymatic reaction products. However, many natural enzymes have inherent defects, limiting their extensive application. Recently, nanozyme-based colorimetric detection has drawn attention due to its merits including high sensitivity, stability under strict reaction conditions, flexible structural design with low-cost materials, and adjustable catalytic activities. This review discusses various nanozyme materials, colorimetric analytic methods and mechanisms, recent machine learning based analytic methods, quantification systems, applications and future directions for monitoring and managing diabetes.

Topics: Algorithms; Biosensing Techniques; Blood Glucose; Blood Glucose Self-Monitoring; Colorimetry; Diabetes Mellitus; Glucose; Humans

PubMed: 36168630
DOI: 10.7150/thno.72152

Review

Authors: Dingran Chang, Sandy Zakaria, Mimi Deng...

Biosensors are analytical devices that have found a variety of applications in medical diagnostics, food quality control, environmental monitoring and biodefense. In recent years, functional nucleic acids, such as aptamers and nucleic acid enzymes, have shown great potential in biosensor development due to their excellent ability in target recognition and catalysis. Deoxyribozymes (or DNAzymes) are single-stranded DNA molecules with catalytic activity and can be isolated to recognize a wide range of analytes through the process of in vitro selection. By using various signal transduction mechanisms, DNAzymes can be engineered into fluorescent, colorimetric, electrochemical and chemiluminescent biosensors. Among them, colorimetric sensors represent an attractive option as the signal can be easily detected by the naked eye. This reduces reliance on complex and expensive equipment. In this review, we will discuss the recent progress in the development of colorimetric biosensors that make use of DNAzymes and the prospect of employing these sensors in a range of chemical and biological applications.

Topics: Biosensing Techniques; Colorimetry; Coloring Agents; DNA, Catalytic; Gold; Metal Nanoparticles

PubMed: 27918487
DOI: 10.3390/s16122061

Authors: Han Yang, Xiaoxin Ji, Xiao Li...

DNA detection, which includes the measurement of variants in sequences or the presence of certain genes, is widely used in research and clinical diagnosis. Both require DNA-dependent DNA polymerase-catalyzed strand extension. Currently, these techniques rely heavily on the instruments used to visualize the results. This study introduced a simple and direct colorimetric method to measure polymerase-directed elongation. First, pyrophosphate (PPi), a by-product of strand extension, is converted into phosphate (Pi). Phosphate levels were measured using either Mo-Sb or BIOMOL Green reagent. This study showed that this colorimetry can distinguish single-base variants and detect PCR products in preset stringent conditions, implicating the potential value of this strategy to detect DNA.

Topics: Colorimetry; DNA; Polymerase Chain Reaction; Nucleic Acid Amplification Techniques; DNA-Directed DNA Polymerase

PubMed: 36726843
DOI: 10.1155/2023/8296847

Review

Authors: Bao Chau K Ly, Ethan B Dyer, Jessica L Feig...

Skin color evaluation contributes to assessment of an individual's cutaneous phenotype. Skin color changes provide important clues to disease progression or treatment response. Skin color is also a predictor of skin cancer risk. Melanin pigment, blood flow, skin thickness, and photoaging contribute to skin color. Melanin, hemoglobin, bilirubin, and carotene are the primary chromophores of skin color. Their concentrations vary depending on the individual's phenotype, anatomic location, external insults of chemical irritants and UVR, and physiological changes. The evaluation and perception of skin color are often subjective. Objective quantification of skin color can be achieved with colorimetric devices such as tristimulus colorimeters. These devices compute the intensity of light reflected from skin and correlate with pigmentation and erythema. Cutaneous color and color changes can be quantified under color organization systems, such as the CIELAB color space, which is standardized by the Commission Internationale de l'Eclairage (CIE). The CIELAB expresses color's lightness, red/green intensity, and yellow/blue intensity, as L*, a*, and b* values, respectively. Additionally, skin color's full spectral characteristics and cutaneous physiology can be measured with spectrophotometers. This article outlines basic principles of the CIELAB color system and how to optimally use colorimetric devices as a skin research tool.

Topics: Colorimetry; Erythema; Humans; Melanins; Skin; Skin Neoplasms; Skin Physiological Phenomena; Skin Pigmentation; Spectrophotometry; Ultraviolet Rays

PubMed: 31864431
DOI: 10.1016/j.jid.2019.11.003

Review

Authors: Xuan Weng, Yuejun Kang, Qian Guo...

Over the past decades, researchers have been seeking attractive substrate materials to keep microfluidics improving to outbalance the drawbacks and issues. Cellulose substrates, including thread, paper and hydrogels are alternatives due to their distinct structural and mechanical properties for a number of applications. Thread have gained considerable attention and become promising powerful tool due to its advantages over paper-based systems thus finds numerous applications in the development of diagnostic systems, smart bandages and tissue engineering. To the best of our knowledge, no comprehensive review articles on the topic of thread-based microfluidics have been published and it is of significance for many scientific communities working on Microfluidics, Biosensors and Lab-on-Chip. This review gives an overview of the advances of thread-based microfluidic diagnostic devices in a variety of applications. It begins with an overall introduction of the fabrication followed by an in-depth review on the detection techniques in such devices and various applications with respect to effort and performance to date. A few perspective directions of thread-based microfluidics in its development are also discussed. Thread-based microfluidics are still at an early development stage and further improvements in terms of fabrication, analytical strategies, and function to become low-cost, low-volume and easy-to-use point-of-care (POC) diagnostic devices that can be adapted or commercialized for real world applications.

Topics: Animals; Biosensing Techniques; Cellulose; Colorimetry; Cotton Fiber; Electrochemical Techniques; Gossypium; Humans; Microfluidic Analytical Techniques; Paper; Point-of-Care Systems

PubMed: 30875629
DOI: 10.1016/j.bios.2019.03.009

Review

Authors: Yanyun Cui, Jun Zhao, Huidan Li...

The colorimetric signal readout method is widely used in visualized analyses for its advantages, including visualization of test results, simple and fast operations, low detection cost and fast response time. Gold nanoparticles (Au NPs), which not only exhibit enzyme-like activity but also have the advantages of tunable localized surface plasmon resonance (LSPR), high stability, good biocompatibility and easily modified properties, provide excellent platforms for the construction of colorimetric sensors. They are widely used in environmental monitoring, biomedicine, the food industry and other fields. This review focuses on the chromogenic mechanisms of colorimetric sensors based on Au NPs adopting two different sensing strategies and summarizes significant advances in Au NP-based colorimetric sensing with enzyme-like activity and tunable LSPR characteristics. In addition, the sensing strategies based on the LSPR properties of Au NPs are classified into four modulation methods: aggregation, surface modification, deposition and etching, and the current status of visual detection of various analytes is discussed. Finally, the review further discusses the limitations of current Au NP-based detection strategies and the promising prospects of Au NPs as colorimetric sensors, guiding the design of novel colorimetric sensors.

Topics: Humans; Metal Nanoparticles; Gold; Colorimetry; Biosensing Techniques; Surface Properties; Static Electricity

PubMed: 37622887
DOI: 10.3390/bios13080801

Review

Authors: Guangyang Liu, Meng Lu, Xiaodong Huang...

Due to their unique optical properties, narrow size distributions, and good biological affinity, gold nanoparticles have been widely applied in sensing analysis, catalytic, environmental monitoring, and disease therapy. The color of a gold nanoparticle solution and its maximum characteristic absorption wavelength will change with the particle size and inter-particle spacing. These properties are often used in the detection of hazardous chemicals, such as pesticide residues, heavy metals, banned additives, and biotoxins, in food. Because the gold nanoparticles-colorimetric sensing strategy is simple, quick, and sensitive, this method has extensive applications in real-time on-site monitoring and rapid testing of food quality and safety. Herein, we review the preparation methods, functional modification, photochemical properties, and applications of gold nanoparticle sensors in rapid testing. In addition, we elaborate on the colorimetric sensing mechanisms. Finally, we discuss the advantages and disadvantages of colorimetric sensors based on gold nanoparticles, and directions for future development.

Topics: Biosensing Techniques; Colorimetry; Food Safety; Gold; Metal Nanoparticles

PubMed: 30486466
DOI: 10.3390/s18124166