Colorimetric biosensing using smart materials

Transcriptional regulator-based biosensors for biomanufacturing in Corynebacterium glutamicum

Intracellular biosensors based on transcriptional regulators have become essential instruments in biomanufacturing, extensively employed for the semi-quantitative assessment of intracellular metabolites, high-throughput screening of production strains, and the directed evolution of enzymes. Corynebacterium glutamicum serves as an industrial chassis for the production of amino acids and a variety of high-value-added chemicals. This paper discusses the varieties and modes of action of transcriptional regulators employed in the construction of intracellular biosensors in C. glutamicum. It also reviews the design principles and progress in the application of transcriptional regulator-based biosensors. Furthermore, measures designed to improve the efficacy of these biosensors are delineated. The challenges and future prospects of biosensors based on transcriptional regulators in practical applications are analyzed. This review seeks to offer theoretical direction for the systematic design and development of transcriptional regulator-based biosensors and to aid researchers in enhancing the growth and productivity of microbial production strains.

Convenient Biochemical Testing Technologies for Oral Disease Risk Warning: Opportunities and Challenges

In recent years, attention toward oral health issues has increased with economic development and improvements in quality of life. Biochemical testing technologies offer an efficient method for identifying insidious pathological changes in the oral cavity. Frequent home-based self-screening can enable early identification of dental disease risks, thus facilitating timely interventions. Convenient home-based biochemical testing methods must be user-friendly, cost-effective, and operable without specialized equipment or extensive training. This review summarizes recent advances in convenient biochemical testing methods for the detection and diagnosis of oral diseases, focusing on their reliability, user compliance, and practicality for home-based applications. This review highlights the significance of biomarker distribution imaging for simultaneously identifying multiple lesions and provides perspectives on future research directions. By promoting interdisciplinary collaboration in biochemical diagnostics, this review outlines pathways toward personalized oral healthcare, precision dentistry, and enhanced overall health outcomes.

Bio-fabrication of chitosan-stabilized magnesium oxide nanomaterials: Investigation of photocatalytic, in vitro cytotoxicity activities and apoptosis in oral squamous carcinoma cells

A bio-fabrication approach is a novel way to develop chitosan-stabilized magnesium oxide nanomaterials (cMgO-NMs). The process involves utilizing polymeric chitosan as the reducing and stabilizing agent. The characteristics of the developed cMgO-NMs were determined using various spectroscopical techniques. Fourier-transform infrared spectroscopy (FTIR) analysis revealed crucial functional groups, Ultraviolet-visible spectroscopy (UV-Vis) spectrum showed nanomaterial development with a peak at 358 nm, and powder X-ray diffraction (PXRD) pattern confirmed a pure cubic crystalline structure. Field emission scanning electron microscopy (FE-SEM) images depicted spherical shape, while energy dispersive X-ray analysis (EDX) confirmed Mg presence. The photocatalytic efficacy of these nanomaterials in degrading dye methylene blue (MB) was examined, and the findings demonstrated the remarkable proficiency of cMgO-NMs in breaking down the dye. The cytotoxic effects of cMgO-NMs were assessed for the first time on PCI-9A and PCI-13 cancer cell lines, yielding an IC50 value of 51 μg/mL and 42 μg/mL. The cMgO-NMs treated PCI-9A and PCI-13 cancer cells morphological changes were observed via acridine orange and ethidium bromide and DAPI staining assay, and apoptotic mode of cell death was examined through flow cytometry and comet assay. Polymeric chitosan proved effective in extensive cMgO-NMs production, showing potential as an anticancer drug, although requiring further preclinical development.

PSMA-targeted delivery of docetaxel in prostate cancer using small-sized PDA-based micellar nanovectors

In this study, we present the first comparative analysis of active and passive drug delivery systems for docetaxel (DTX) in prostate cancer using supramolecular self-assembled micellar nanovectors. Specifically, we developed two novel micelles based on polydiacetylenic amphiphiles (PDA) for passive and active targeting. The active targeting micelles were designed with a prostate-specific membrane antigen (PSMA) ligand, ACUPA, to facilitate recognition by PSMA-positive cancer cells. These PDA-based micelles feature a well-defined structure with a hydrophobic PDA core and a surface functionalized with PEG, and for active targeting, ACUPA. Our micelles demonstrated excellent encapsulation capacity, significantly improving DTX solubility in water, a crucial factor for clinical drug use. In vitro studies confirmed the safety and cytotoxic profiles of both systems, with ACUPA-functionalized micelles showing notable internalization into PSMA-positive LNCaP cells, mediated through the PSMA-ACUPA interaction. In vivo imaging revealed preferential accumulation of ACUPA-functionalized nanomicelles in LNCaP xenograft tumors, suggesting enhanced retention via specific ACUPA-PSMA interactions and active uptake by LNCaP cells. Notably, Balb/c-Foxn1nu/nu early in vivo studies showed a marked reduction in tumor volume and tumor expression levels of proliferation, cell cycle progression, cell survival and anti-apoptotic markers with DTX-loaded micelles functionalized with ACUPA compared to those without ACUPA. Overall, our studies collect initial evidence regarding the feasibility of supramolecular self-assembly of ACUPA-PDA-based nanomicelles for PSMA-targeted drug chemotherapy delivery developments.

Design and Synthesis of Multi-compartment Microcapsules via Pickering Emulsion Polymerization for Infrared Stealth and Adaptive Camouflage Applications

High-performance color-changing compounds, recognized as prominent smart materials, dynamically alter their color in response to external environmental stimuli. However, existing compounds exhibit limited responsiveness and color diversity, presenting challenges in the development of textiles responsive to multiple stimuli. This research introduces a novel design for dual-responsive color-changing microcapsules, employing a Pickering emulsion template method. The larger compartment encloses photosensitive dyes, whereas the smaller one contains thermochromic phase-change colorants. Adjusting the density of nanocapsules in the smaller compartment on the microcapsule surface enables a spectrum of colors, including red, yellow, blue, and green, triggered by light and heat. When incorporated into textiles, these microcapsules bestow adaptive color-changing attributes and infrared stealth capabilities onto the fabrics. Additionally, by modulating the color via surface micro/nanostructures, textile surfaces can exhibit hydrophobic and oleophobic properties. Such enhancements extend the textiles' potential applications in areas like anti-counterfeiting and military operations.

2D Fe/Co-MOF/SOX cascade reactors for fast noninvasive detection of sarcosine level in prostate cancer urine

Sarcosine plays a key role in screening for early prostate cancer. However, the several already reported peroxidase mimics immobilized with sarcosine oxidase (SOX) utilized to detect uriary sarcosine still have some limitations such as complex synthesis process, using of expensive heavy metals to mimic enzyme activity and long color development time. Herein, an inexpensive peroxidase-like 2D Fe/Co-MOF nanosheet was prepared by a simple solvent modulation method. The resultant 2D Fe/Co-MOF nanosheets have strong peroxidase activity, with its Vmax value for H2O2 of 15.3 × 10-8 M/s, being 1.76 times that of HRP. Then, using the 2D Fe/Co-MOF as a peroxidase model for anchoring natural SOX to construct 2D Fe/Co-MOF/SOX , which can act as a cascade reactor for detection of sarcosine. Considering the above properties, a platform for the detection of sarcosine was built based on a colorimetric method. Because of presence of the high ratio of Fe2+ caused by the electron transfer from Co2+ to Fe3+, large specific surface area and plentiful active sites, 2D Fe/Co-MOF/SOX with TMB (3,3',5,5'-tetramethylbenzidine) colorimetric reagent could have fast color development and can be applied conveniently and fastly in an early screening tool for prostate cancer patients. The sarcosine could be quantified by peroxidase activity with a detection range of 1-400 μM and a limit of detection (LOD) of 0.324 μM. More importantly, the average sarcosine concentration of 21.367 μM and 1.871 μM was detected in patient's and normal urine (n = 5), respectively, which showed an excellent screening effect and a great potential in early prostate cancer.

Fabrication of natural enzyme-covered / amino-modified Pd-Pt bimetallic-doped zeolitic imidazolate framework for ultrasensitive detection of metabolites

The present article introduced an natural enzyme-covered/amino-modified Pd-Pt bimetallic-doped zeolitic imidazolate framework (NAPPZ) for ultrasensitive and specific detection of glucose. The dodecahedral nanomaterial zeolitic imidazolate framework (ZIF-8)-loaded Pd-Pt bimetallic nanoparticles endowed the composite with peroxidase-like activity. The modification with glucose oxidase (GOx) facilitated the rapid access of H2O2 produced through glucose oxidation to the Pd-Pt nanoparticles vicinity reducing diffusion. GOx specifically catalyzes the transformation of glucose into H2O2, which then H2O2 rapidly migrates to the Pd-Pt nanoparticles, catalyzing the oxidation of colorless o-phenylenediamine into the orange-yellow product 2,3-diaminophenazine. Based on the aforementioned cascade reaction, the NAPPZ and NAPPZ based on ChOx were utilized for detecting glucose in human urine samples and cholesterol in milk, respectively. The NAPPZ strategy presented a broad detection range (20-1100 μmol L-1) and a low detection limit (15.9 μmol L-1) for glucose, and the NAPPZ based on ChOx strategy approach offered a broad detection range (10-500 μmol L-1) and low detection limit (6.4 μmol L-1) for cholesterol. Therefore, this novel method holds significant potential in the areas of clinical diagnostics and food safety.

Development of a Novel Colorimetric pH Biosensor Based on A-Motif Structures for Rapid Food Freshness Monitoring and Spoilage Detection

Accurate methods for assessing food freshness through colorimetric pH response play a critical role in determining food spoilage and ensuring food quality standards. This study introduces a novel unlabeled DNA sequence, poly-dA20, designed to exploit the colorimetric properties of both the single strand and the fold-back A-motif structure in conjunction with gold nanoparticles (AuNPs) under varying pH conditions. When exposed to storage temperatures of 4 °C and 25 °C, the color variations in the AuNP solution, influenced by pH level changes in mutton and sea bass samples' different storage periods, are easily discernible to the naked eye within a minute. The ratio of UV absorption values at 527 nm and 700 nm (A527/A700) demonstrates a strong linear correlation with both the storage duration and pH of the food samples. Furthermore, a comprehensive analysis combining the total volatile basic nitrogen (TVB-N) value with the A527/A700 ratio is employed for precise assessment of food freshness. The innovative pH-responsive sensing strategy not only provides a new approach for on-site food freshness and spoilage detection systems but also serves as a valuable tool for pH-related biological detection in clinical diagnostic applications.

Layered Architectural Fabrication of a Novel Sulfite Nanobiosensor by Encapsulation of Sulfite Oxidase on a Polypyrrole-Multiwalled Carbon Nanotubes Composite Decorated with Platinum Nanoparticles

The fabrication of a highly selective and ultrasensitive sulfite nanobiosensor based on a layered architectural fabrication aided by the encapsulation of sulfite oxidase (SOx) in Nafion (Naf) matrix on a multiwalled carbon nanotubes-polypyrrole (MWCNTs-PPy) composite decorated with platinum nanoparticles (PtNPs) is described. The MWCNTs are deposited in the inner layer on a Pt electrode during electropolymerization of pyrrole (Py), followed by decoration with a PtNPs layer and subsequent encapsulation of SOx with Naf in the third layer capped with a fourth thin PtNPs layer. Images obtained by field emission scanning electron microscopy (FESEM) reveal that high-density PtNPs are deposited onto the 3D nanostructured inner MWCNTs-PPy layer and the electrochemical behavior is investigated. A large surface area provided by the incorporation of MWCNTs in the composite and decoration with PtNPs enables increased SOx loading, SOx retention, and substantial improvement in sensing performance. The resulting layered PtNPs/SOx-Naf/PtNPs/MWCNTs-PPy nanobiosensor exhibits a fast response time (within 3 s), a linear calibration range of 20 nmm - 6 m with an excellent sensitivity of 71 µA mm-1 cm-2 and a detection limit of 5.4 nm. The nanobiosensor  was effective in discriminating against common interferants and  was successfully applied to sulfite determination in real samples.

Customizable Colorimetric Sensor Array via a High-Throughput Robot for Mitigation of Humidity Interference in Gas Sensing

One challenge for gas sensors is humidity interference, as dynamic humidity conditions can cause unpredictable fluctuations in the response signal to analytes, increasing quantitative detection errors. Here, we introduce a concept: Select humidity sensors from a pool to compensate for the humidity signal for each gas sensor. In contrast to traditional methods that extremely suppress the humidity response, the sensor pool allows for more accurate gas quantification across a broader range of application scenarios by supplying customized, high-dimensional humidity response data as extrinsic compensation. As a proof-of-concept, mitigation of humidity interference in colorimetric gas quantification was achieved in three steps. First, across a ten-dimensional variable space, an algorithm-driven high-throughput experimental robot discovered multiple local optimum regions where colorimetric humidity sensing formulations exhibited high evaluations on sensitivity, reversibility, response time, and color change extent for 10-90% relative humidity (RH) in room temperature (25 °C). Second, from the local optimum regions, 91 sensing formulations with diverse variables were selected to construct a parent colorimetric humidity sensor array as the sensor pool for humidity signal compensation. Third, the quasi-optimal sensor subarrays were identified as customized humidity signal compensation solutions for different gas sensing scenarios across an approximately full dynamic range of humidity (10-90% RH) using an ingenious combination optimization strategy, and two accurate quantitative detections were attained: one with a mean absolute percentage error (MAPE) reduction from 4.4 to 0.75% and the other from 5.48 to 1.37%. Moreover, the parent sensor array's excellent humidity selectivity was validated against 10 gases. This work demonstrates the feasibility and superiority of robot-assisted construction of a customizable parent colorimetric sensor array to mitigate humidity interference in gas quantification.

Lysozyme-sensitive plasmonic hydrogel nanocomposite for colorimetric dry-eye inflammation biosensing

Detection of lysozyme levels in ocular fluids is considered crucial for diagnosing and monitoring various health and eye conditions, including dry-eye syndrome. Hydrogel-based nanocomposites have been demonstrated to be one of the most promising platforms for fast and accurate sensing of different biomolecules. In this work, hydrogel, electrospun nanofibers, and plasmonic nanoparticles are combined to fabricate a sensitive and easy-to-use biosensor for lysozyme. Poly(L-lactide-co-caprolactone) (PLCL) nanofibers were covered with silver nanoplates (AgNPls), providing a stable plasmonic platform, where a poly(N-isopropylacrylamide)-based (PNIPAAm) hydrogel layer allows mobility and good integration of the biomolecules. By integrating these components, the platform can also exhibit a colorimetric response to the concentration of lysozyme, allowing for easy and non-invasive monitoring. Quantitative biosensing operates on the principle of localized surface plasmon resonance (LSPR) induced by plasmonic nanoparticles. Chemical, structural, thermal, and optical characterizations were performed on each platform layer, and the platform's ability to detect lysozyme at concentrations relevant to those found in tears of patients with dry-eye syndrome and other related diseases was investigated by colorimetry and UV-Vis spectroscopy. This biosensor's sensitivity and rapid response time, alongside the easy detection by the naked eye, make it a promising tool for early diagnosis and treatment monitoring of eye diseases.

Functionalized Chiral Materials for Use in Chiral Sensors

Chirality represents a fundamental attribute within living systems and is a pervasive phenomenon in the natural world. The identification and analysis of chiral materials within natural environments and biological systems hold paramount importance in clinical, chemical, and biological sciences. Within chiral analysis, there is a burgeoning focus on developing chiral sensors exhibiting exceptional selectivity, sensitivity, and stability, marking it as a forefront area of research. In the past decade (2013-2023), approximately 1990 papers concerning the application of various chiral materials in chiral sensors have been published. Biological materials and nanomaterials have important applications in the development of chiral sensors, which accounting for 26.67% and 45.24% of the material-related applications in these sensors, respectively; moreover, the development of chiral nanomaterials is closely related to the development of portable and stable chiral sensors. Natural chiral materials, utilized as selective recognition units, are combined with carriers characterized by good physical and chemical properties through functionalization to form various functional chiral materials, which improve the recognition efficiency of chiral sensors. In this article, from the perspective of biological materials, polymer materials, nanomaterials, and other functional chiral materials, the applications of chiral sensors are summarized and the research prospects of chiral sensors are discussed.

A papain-based colorimetric catalytic sensing system for immunoassay detection of carcinoembryonic antigen

A colorimetric immunoassay was built for determination of carcinoembryonic antigen (CEA) based on papain-based colorimetric catalytic sensing system through the use of glucose oxidase (GOx). In the presence of GOx, glucose was catalytically oxidized to produce H2O2. Through the assistance of papain (as a peroxide mimetic enzyme), the signal came from the oxidative color development of 3,3',5,5'-tetramethylbenzidine (TMB, from colorless to blue) catalyzed by the generated H2O2. Herein, a sandwich-type immunoassay was built based on GOx as labels. As the concentration of CEA increased, more GOx-labeled antibodies specifically associate with target, which leaded to more H2O2 generation. Immediately following this, more TMB were oxidized with the addition of papain. Accordingly, the absorbance increased further. As a result, the concentration of CEA is positively correlated with the change in absorbance of the solution. Under optimal conditions, the CEA concentration was linear in the range of 0.05-20.0 ng/mL, and the limit of detection (LOD) reached 37 pg/mL. The papain-based colorimetric immunoassay also exhibited satisfactory repeatability, stability, and selectivity.

Microfluidic chemistry assisted synthesis of cobalt quantum dot embedded nitrogen doped carbon with oxidase-like properties toward ascorbic acid detection

Ascorbic acid (AA) is a powerful antioxidant in food safety and disease treatment. It is of great significance to develop a low-cost, high-stability, and easy-to-operate colorimetric method for quantitative detection of AA in food or human body. Although various nanozymes have been developed for the colorimetric detection of AA, the size regulation of the catalytic center of nanozymes remains a challenge. In this work, we propose a combined strategy of flow chemistry synthesis and pyrolysis to realize the controllable adjustment of the catalytic center size of nanozymes. Zinc-cobalt zeolitic imidazole frameworks (ZnCo-ZIFs) with different sizes are synthesized by flow chemistry. Nitrogen-doped carbon materials with different Co catalytic centers (80 nm-10 nm) are then obtained by pyrolysis of ZnCo-ZIFs precursors. Among them, cobalt quantum dot embedded nitrogen-doped carbon (Co QDs/N-C) exhibits excellent oxidase activity, with Vmax and Km of 4.19 × 10-7 M s-1 and 0.12 mM. Therefore, a simple, low-cost, and stable colorimetric method for the detection of AA is established with a good linear relationship (3-500 μM) and low detection limit (0.40 μM). This work has certain guiding significance for the size regulation of catalytic center of nanozyme, and the detection method has broad application prospects in biochemical sensing field.

Advancements in magnetic nanoparticle-based biosensors for point-of-care testing

The significance of point-of-care testing (POCT) in early clinical diagnosis and personalized patient care is increasingly recognized as a crucial tool in reducing disease outbreaks and improving patient survival rates. Within the realm of POCT, biosensors utilizing magnetic nanoparticles (MNPs) have emerged as a subject of substantial interest. This review aims to provide a comprehensive evaluation of the current landscape of POCT, emphasizing its growing significance within clinical practice. Subsequently, the current status of the combination of MNPs in the Biological detection has been presented. Furthermore, it delves into the specific domain of MNP-based biosensors, assessing their potential impact on POCT. By combining existing research and spotlighting pivotal discoveries, this review enhances our comprehension of the advancements and promising prospects offered by MNP-based biosensors in the context of POCT. It seeks to facilitate informed decision-making among healthcare professionals and researchers while also promoting further exploration in this promising field of study.

Sandwich-type aptamer-based biosensors for thrombin detection

Thrombin, a proteolytic enzyme, plays an essential role in catalyzing many blood clotting reactions. Thrombin can act as a marker for some blood-related diseases, such as leukemia, thrombosis, Alzheimer's disease and liver disease. Therefore, its diagnosis is of great importance in the fields of biological and medical research. Biosensors containing sandwich-type structures have attracted much consideration owing to their superior features such as reproducible and stable responses with easy improvement in the sensitivity of detection. Sandwich-type platforms can be designed using a pair of receptors that are able to bind to diverse locations of the same target. Herein, we investigate recent advances in the progress and applications of thrombin aptasensors containing a sandwich-type structure, in which two thrombin-binding aptamers (TBAs) identify different parts of the thrombin molecule, leading to the formation of a sandwich structure and ultimately signal detection. We also discuss the pros and cons of these approaches and outline the most logical approach in each section.

Biomarkers for Early Cancer Detection: A Landscape View of Recent Advancements, Spotlighting Pancreatic and Liver Cancers

Cancer is one of the leading causes of death worldwide. Early cancer detection is critical because it can significantly improve treatment outcomes, thus saving lives, reducing suffering, and lessening psychological and economic burdens. Cancer biomarkers provide varied information about cancer, from early detection of malignancy to decisions on treatment and subsequent monitoring. A large variety of molecular, histologic, radiographic, or physiological entities or features are among the common types of cancer biomarkers. Sizeable recent methodological progress and insights have promoted significant developments in the field of early cancer detection biomarkers. Here we provide an overview of recent advances in the knowledge related to biomolecules and cellular entities used for early cancer detection. We examine data from the CAS Content Collection, the largest human-curated collection of published scientific information, as well as from the biomarker datasets at Excelra, and analyze the publication landscape of recent research. We also discuss the evolution of key concepts and cancer biomarkers development pipelines, with a particular focus on pancreatic and liver cancers, which are known to be remarkably difficult to detect early and to have particularly high morbidity and mortality. The objective of the paper is to provide a broad overview of the evolving landscape of current knowledge on cancer biomarkers and to outline challenges and evaluate growth opportunities, in order to further efforts in solving the problems that remain. The merit of this review stems from the extensive, wide-ranging coverage of the most up-to-date scientific information, allowing unique, unmatched breadth of landscape analysis and in-depth insights.

Gum Arabic-mediated synthesis of silver nanoparticles for their applications as colorimetric and SERS-based detection of hydrogen peroxide

We report on the one-step green method to synthesize Gum Arabic stabilized silver nanoparticles (GA-Ag NPs). The synthesized particles are monodispersed and in the size range of 15-20 nm. The synthesized Ag NPs are used as a colorimetric sensor for the detection of H2O2 and glucose with a detection limit of 11.7 nM and 0.13 µM, respectively. The sensor has also been used for the detection of H2O2 in water samples and glucose in human blood serum samples. The GA-Ag NPs decorated on filter paper have also shown excellent SERS activity for the detection of H2O2 with a detection limit of 0.56 µM.

Role of pretty nanoflowers as novel versatile analytical tools for sensing in biomedical and bioanalytical applications

In recent years, an encouraging breakthrough in the synthesis of immobilized enzymes in flower-shaped called "organic-inorganic hybrid nanoflowers (hNFs)" with greatly enhanced catalytic activity and stability were reported. Although, these hNFs were discovered by accident, the enzymes exhibited highly enhanced catalytic activities and stabilities in the hNFs compared with the free and conventionally immobilized enzymes. Herein, we rationally utilized the catalytic activity of the hNFs for analytical applications. In this comprehensive review, we covered the design and use of the hNFs as novel versatile sensors for electrochemical, colorimetric/optical and immunosensors-based detection strategies in analytical perspective.

Advances in colorimetric biosensors of exosomes: novel approaches based on natural enzymes and nanozymes

Exosomes are 30-150 nm vesicles derived from diverse cell types, serving as one of the most important biomarkers for early diagnosis and prognosis of diseases. However, the conventional detection method for exosomes faces significant challenges, such as unsatisfactory sensitivity, complicated operation, and the requirement of complicated devices. In recent years, colorimetric exosome biosensors with a visual readout underwent rapid development due to the advances in natural enzyme-based assays and the integration of various types of nanozymes. These synthetic nanomaterials show unique physiochemical properties and catalytic abilities, enabling the construction of exosome colorimetric biosensors with novel principles. This review will illustrate the reaction mechanisms and properties of natural enzymes and nanozymes, followed by a detailed introduction of the recent advances in both types of enzyme-based colorimetric biosensors. A comparison between natural enzymes and nanozymes is made to provide insights into the research that improves the sensitivity and convenience of assays. Finally, the advantages, challenges, and future directions of enzymes as well as exosome colorimetric biosensors are highlighted, aiming at improving the overall performance from different approaches.

A designed DNA/amino acid amphiphile-based supramolecular oxidase-mimetic catalyst for colorimetric DNA detection

DNA is self-assembled with Fmoc-amino acids and Cu2+ to construct a supramolecular catechol oxidase-mimetic catalyst, which exhibits remarkable activity in catalyzing colorimetric reactions. This catalytic system is used for the detection of DNA hybridization with a high selectivity and a low detection limit.

A highly sensitive method for the detection of p-Aminophenol based on Cu-Au nanoparticles and KIO3

BACKGROUND

As a common industrial raw material and chemical intermediate, p-Aminophenol (pAP) is recognized as a serious pollutant that poses harm to both the environment and human health. The traditional detection methods for pAP have the advantages of good selectivity and high sensitivity, but their complex operation and time-consuming defects limit their application in on-site detection. Therefore, it is necessary to develop a simple, low-cost, rapid and high-sensitivity method for the detection of pAP.

RESULTS

Noble metal nanoparticles have been widely used in colorimetric sensing because of their simplicity and practicality. Herein, we presented a simple, excellent sensitive and selective colorimetric method for high-performance detection of pAP based on Cu-Au nanoparticles (Cu-Au NPs) and KIO3. In the presence of pAP, KIO3 was reduced to I2, which subsequently chemically adsorbed onto Cu-Au NPs surface and induced the dispersion and reorganization of Cu-Au NPs, along with prominent color change of the dispersion from gray-blue to pink and the transformation of Cu-Au NPs from chain-like aggregates to individual dispersed, irregular, subspherical nanoparticles. The mechanism was verified by TEM, DLS, Zeta potential, UV-vis and XPS. Meanwhile, Cu-Au NPs probe can rapidly detect pAP within 25 min, the limit of detection of pAP probe is 5 μM by the naked eyes and 0.03 μM by UV-vis absorption spectrum.

SIGNIFICANCE AND NOVELTY

This is the first colorimetric assay for pAP based on Cu-Au NPs probe. The satisfactory linearity (R2 = 0.9984) indicates that the colorimetric probe based on Cu-Au NPs and KIO3 can be utilized for quantitative detection of pAP. The detection results of pAP in real environmental water samples, urine samples and paracetamol tables demonstrate the practicability of pAP colorimetric probe.

The colorimetry and smartphone determination of perfluorooctane sulfonate based on cytidine 5'-monophosphate-capped gold nanoclusters with peroxidase-like activity

Besides being a luminescent material, cytidine 5'-monophosphate-capped gold nanoclusters (AuNCs@CMP) also show superior peroxidase-like activity which can promote TMB oxidation in the presence of H₂O₂, causing the solution to turn efficiently from pale to blue. However, the presence of perfluorooctane sulfonate (PFOS) in the above system inhibited TMB oxidation and bluing of the solution, consequently establishing a colorimetric platform of AuNCs/H₂O₂/TMB for PFOS determination. The results showed that it responded to PFOS over a wide range of 2.0-50 μM, with a limit of detection (LOD) as low as 150 nM. Furthermore, in-depth mechanism investigation revealed that, rather than the active site of the catalyst being occupied by PFOS, such a hypochromatic effect originated from depletion of the reactive oxygen species (ROS) by PFOS degradation, thereby also offering a unique strategy to scavenge the lethal toxicity of PFOS. In addition, the colorimetric response of AuNCs/H₂O₂/TMB to PFOS was extended to smartphone determination conveniently based on RGB values. Finally, the established platform was applied to PFOS determination both in soil extracts and in tap water with good recovery, which supplies a novel colorimetric platform for visual determination of PFOS in practice. The method has the advantages of being rapid, sensitive and highly selective, which highlight the design and construction of more systems for determination and elimination of lethal pollutants in environmental water.

An ultrasensitive colorimetric biosensor for the detection of Gram-positive bacteria by integrating paper-based enrichment and carbon dot-based selective recognition

Rapid screening of bacteria by low-cost and eco-friendly material-based approaches is still a major challenge. Herein, a colorimetric biosensor was designed for the ultrasensitive and rapid detection of Gram-positive bacteria. The biosensor exploited polydopamine and polyethyleneimine (PDA-PEI)-modified papers for separating bacteria and carbon dots (CDs) for selective colorimetric detection of Gram-positive bacteria. Noble metal-free CDs can target Gram-positive bacteria by binding with peptidoglycan and possess peroxidase-like activity. Thus, they can avert the step of modifying recognition probes, facilitating biosensor fabrication, and reducing the cost. This biosensor can detect S. aureus as low as 1 cfu mL^-1, L. monocytogenes as low as 5 cfu mL^-1, and B. subtilis as low as 9 cfu mL^-1 within 55 min. In addition, a portable device was constructed to enable convenient and on-site quantitative detection of Gram-positive bacteria. The feasibility of the biosensor was verified by detecting Gram-positive bacteria in eggshell and sausage samples with recoveries ranging from 91.2% to 110%.

Aptamer-based colorimetric and lateral flow assay approaches for the detection of toxic metal ions, thallium(i) and lead(ii)

Thallium(i) and lead(ii) ions are heavy metals and extremely toxic. These metals are environmental pollutants, posing a severe risk to the environment and human health. In this study, two approaches were examined using aptamer and nanomaterial-based conjugates for thallium and lead detection. The first approach utilized an in-solution adsorption-desorption approach to develop colorimetric aptasensors for the detection of thallium(i) and lead(ii) using gold or silver nanoparticles. The second approach was the development of lateral flow assays, and their performance was tested with thallium (limit of detection is 7.4 μM) and lead ion (limit of detection is 6.6 nM) spiked into real samples. The approaches assessed are rapid, inexpensive, and time efficient with the potential to become the basis for future biosensor devices.

Rapid and selective colorimetric determination of L-DOPA in human serum with silver nanoparticles

L-DOPA, or l-3,4-dihydroxyphenylalanine is an aromatic amino acid, which plays a significant role in human metabolism as a precursor of important neurotransmitters. We develop a fast and simple colorimetric method for the detection of L-DOPA in biological fluids. The method is based on the reduction of silver ions with L-DOPA and the subsequent formation of L-DOPA stabilized silver nanoparticles (Ag NPs). In this novel approach, L-DOPA works as both reducing and stabilizing agent, which provides selectivity and simplifies the procedure. HR-TEM images show very narrow Ag NPs distribution with an average size of 24 nm. Such sensor design is suggested for the first time. We also calculate vertical ionization potential, vertical electron affinity, and Gibbs free energy change of different ionic forms of L-DOPA and amino acids at the M06-2X/def2-TZVP level for the gas phase in comparison with that of silver. A model of silver ions reduction by aromatic amino acids is proposed: the ionic forms with charge -1 are suggested to reduce silver ions. High selectivity against aromatic amino acids, dopamine and serotonin is achieved by tuning pH and involving two L-DOPA forms with charged both hydroxyphenolate and carboxylate groups in the stabilization of uniform-sized Ag NPs. The method is applicable for the determination of L-DOPA in human serum with the 50 nM limit of detection and the linear range up to 5 μM. Ag NPs formation and coloring the solution proceeds in a few minutes. The suggested colorimetric method has potential application in clinical trials.

Emerging trends in point-of-care biosensing strategies for molecular architectures and antibodies of SARS-CoV-2

COVID-19, a highly contagious viral infection caused by the occurrence of severe acute respiratory syndrome coronavirus (SARS-CoV-2), has turned out to be a viral pandemic then ravaged many countries worldwide. In the recent years, point-of-care (POC) biosensors combined with state-of-the-art bioreceptors, and transducing systems enabled the development of novel diagnostic tools for rapid and reliable detection of biomarkers associated with SARS-CoV-2. The present review thoroughly summarises and discusses various biosensing strategies developed for probing SARS-CoV-2 molecular architectures (viral genome, S Protein, M protein, E protein, N protein and non-structural proteins) and antibodies as a potential diagnostic tool for COVID-19. This review discusses the various structural components of SARS-CoV-2, their binding regions and the bioreceptors used for recognizing the structural components. The various types of clinical specimens investigated for rapid and POC detection of SARS-CoV-2 is also highlighted. The importance of nanotechnology and artificial intelligence (AI) approaches in improving the biosensor performance for real-time and reagent-free monitoring the biomarkers of SARS-CoV-2 is also summarized. This review also encompasses existing practical challenges and prospects for developing new POC biosensors for clinical monitoring of COVID-19.

Genetically engineered bacterium-modified magnetic particles assisted chiral recognition and colorimetric determination of D/L-tryptophan in millets

Chiral recognition of enantiomers has always been a thorny issue since they exhibit the same properties under an achiral environment. Herein, polydopamine-functionalized magnetic particles (MP@PDA) were synthesized to immobilize the genetically engineered bacterium Escherichia coli DH5α (MP@PDA-E. coli). L-tryptophan (Trp) instead of D-Trp can be stereo-specifically degraded by tryptophanase in E. coli. The degradation product indole reacts with 4-dimethylaminobenzaldehyde to generate a rose-red adduct. Thus, MP@PDA-E. coli was employed to fabricate a chiral colorimetric method for chiral recognition and determination of L-Trp. The method averts the purification of tryptophanase. More importantly, tryptophanase demonstrates excellent enantioselective ability for L-Trp. The method can not only quantitatively detect L-Trp but also realize the measurement of the enantiomer percentage in the enantiomeric mixture. The feasibility was verified by detecting L-Trp in millet samples from different origins. Furthermore, a portable device was fabricated to make the method more convenient.

Anti-CD44 antibodies grafted immunoaffinity Fe3O4@MnO2 nanozymes with highly oxidase-like catalytic activity for specific detection of triple-negative breast cancer MDA-MB-231 cells

Cell-enzyme-linked immunosorbent assay (CELISA) is extensively applied for cancer diagnosis and screening because of its simple operation, high sensitivity, and intuitive color change. However, the unstable horseradish peroxidase (HRP), hydrogen peroxide (H₂O₂) and non-specificity have led to a high false negative rate, which limits its application. In this study, we have developed an innovative immunoaffinity nanozyme aided CELISA based on anti-CD44 monoclonal antibodies (mAbs) bioconjugated manganese dioxide-modified magnetite nanoparticles (Fe₃O₄@MnO₂ NPs) for the specific detection of triple-negative breast cancer MDA-MB-231 cells. The ^CD44FM nanozymes were fabricated to replace unstable HRP and H₂O₂ to counteract possible negative effects in conventional CELISA. Results suggested that ^CD44FM nanozymes displayed remarkable oxidase-like activities over an extensive pH and temperature range. The bioconjugation of CD44 mAbs enabled ^CD44FM nanozymes to enter MDA-MB-231 cells selectively via over-expressed CD44 antigens on the membrane surface of these cells, and then catalyzed oxidation of the chromogenic substrate TMB, further achieving specific detection of these cells. Additionally, this study exhibited high sensitivity and low detection limit for MDA-MB-231 cells with a quantitation range of just 186 cells. To sum up, this report developed a simple, specific and sensitive assay platform based on ^CD44FM nanozymes, which could provide a promising strategy for targeted diagnosis and screening of breast cancer.

Ultrasensitive determination of α-glucosidase activity using CoOOH nanozymes and its application to inhibitor screening

In this work, a novel method for the colorimetric sensing of α-glucosidase (α-Glu) activity was developed based on CoOOH nanoflakes (NFs), which exhibit efficient oxidase-mimicking activity. Colorless 3,3',5,5'-tetramethylbenzidine (TMB) can be oxidized by CoOOH NFs into blue-colored oxidized TMB (oxTMB) in the absence of H₂O₂. L-Ascorbic acid-2-O-α-D-glucopyranose (AAG) can be hydrolysed by α-glucosidase to produce ascorbic acid, resulting in a significant decrease of catalytic activity of CoOOH NFs. Thus, a colorimetric α-glucosidase activity detection method was designed with a limit of detection of 0.0048 U mL^-1. Furthermore, the designed sensing platform exhibits favorable applicability for the α-glucosidase (α-Glu) activity assay in real samples. Meanwhile, this method can be expanded to study the inhibitors of α-Glu. Finally, the as-proposed method combined with a smartphone would be a color recognizer, which was successfully applied for the determination of α-Glu activity in human serum samples.

Antibacterial Enhancement of High-Efficiency Particulate Air Filters Modified with Graphene-Silver Hybrid Material

Bacterial infections are a major concern as antibiotic resistance poses a great threat, therefore leading to a race against time into finding new drugs or improving the existing resources. Nanomaterials with high surface area and bactericidal properties are the most promising ones that help combating microbial infections. In our case, graphene decorated with silver nanoparticles Gr-Ag (5 wt% Ag) exhibited inhibitory capacity against S. aureus and E. coli. The newly formed hybrid material was next incubated with high-efficiency particulate air (HEPA) filter, to obtain one with bactericidal properties. The modified filter had greater inhibitory action against the tested strains, compared to the control, and the effect was better against the Gram-negative model. Even if the bacteria remained attached to the filters, their colony forming unit capacity was affected by the Gr-Ag (5 wt% Ag) hybrid material, when they were subsequently re-cultured on fresh agar media. Therefore, the HEPA filter modified with Gr-Ag (5 wt% Ag) has high antibacterial properties that may substantially improve the existing technology.

An Ultrasensitive Colorimetric Foodborne Pathogenic Detection Method Using a CRISPR/Cas12a Mediated Strand Displacement/Hybridization Chain Reaction

Accurate, rapid, and sensitive pathogenic detections play an important role in food safety. Herein, we developed a novel CRISPR/Cas12a mediated strand displacement/hybridization chain reaction (CSDHCR) nucleic acid assay for foodborne pathogenic colorimetric detection. A biotinylated DNA toehold is coupled on avidin magnetic beads and acts as an initiator strand to trigger the SDHCR. The SDHCR amplification allowed the formation of long hemin/G-quadruplex-based DNAzyme products to catalyze the TMB-H₂O₂ reaction. In the presence of the DNA targets, the trans-cleavage activity of CRISPR/Cas12a was activated to cleave the initiator DNA, resulting in the failure of SDHCR and no color change. Under optimal conditions, the CSDHCR has a satisfactory linear detection of DNA targets with a regression equation Y = 0.0531*X - 0.0091 (R² = 0.9903) in the range of 10 fM to 1 nM, and the limit of detection was determined as 4.54 fM. In addition, Vibrio vulnificus, one foodborne pathogen, was used to verify the practical application of the method, and it showed satisfactory specificity and sensitivity with a limit of detection at 1.0 × 10⁰ CFU/mL coupling with recombinase polymerase amplification. Our proposed CSDHCR biosensor could be a promising alternative method for ultrasensitive and visual detection of nucleic acids and the practical application of foodborne pathogens.

Carbon Nanostructure Embedded Novel Sensor Implementation for Detection of Aromatic Volatile Organic Compounds: An Organized Review

For field-like environmental gas monitoring and noninvasive illness diagnostics, effective sensing materials with exceptional sensing capabilities of sensitive, quick detection of volatile organic compounds (VOCs) are required. Carbon-based nanomaterials (CNMs), like CNTs, graphene, carbon dots (Cdots), and others, have recently drawn a lot of interest for their future application as an elevated-performance sensor for the detection of VOCs. CNMs have a greater potential for developing selective sensors that target VOCs due to their tunable chemical and surface properties. Additionally, the mechanical versatility of CNMs enables the development of novel gas sensors and places them ahead of other sensing materials for wearable applications. An overview of the latest advancements in the study of CNM-based sensors is given in this comprehensive organized review.

Recent Progress on Optical Biosensors Developed for Nucleic Acid Detection Related to Infectious Viral Diseases

Optical biosensors have many advantages over traditional analytical methods. They enable the identification of several biological and chemical compounds directly, instantly, and without the need of labels. Their benefits include excellent specificity, sensitivity, compact size, and low cost. In this review, the main focus is placed on the nucleic acid-based optical biosensor technologies, including colorimetric, fluorescence, surface plasmon resonance (SPR), Evanescent-Wave Optical, Fiber optic and bioluminescent optical fibre. The fundamentals of each type of biosensor are briefly explained, and particular emphasis has been placed on the achievements which have been gained in the last decade on the field of diagnosis of infectious viral diseases. Concluding remarks concerning the perspectives of further developments are discussed.

Aptamer-based rapid diagnosis for point-of-care application

Aptasensors have attracted considerable interest and widespread application in point-of-care testing worldwide. One of the biggest challenges of a point-of-care (POC) is the reduction of treatment time compared to central facilities that diagnose and monitor the applications. Over the past decades, biosensors have been introduced that offer more reliable, cost-effective, and accurate detection methods. Aptamer-based biosensors have unprecedented advantages over biosensors that use natural receptors such as antibodies and enzymes. In the current epidemic, point-of-care testing (POCT) is advantageous because it is easy to use, more accessible, faster to detect, and has high accuracy and sensitivity, reducing the burden of testing on healthcare systems. POCT is beneficial for daily epidemic control as well as early detection and treatment. This review provides detailed information on the various design strategies and virus detection methods using aptamer-based sensors. In addition, we discussed the importance of different aptamers and their detection principles. Aptasensors with higher sensitivity, specificity, and flexibility are critically discussed to establish simple, cost-effective, and rapid detection methods. POC-based aptasensors' diagnostic applications are classified and summarised based on infectious and infectious diseases. Finally, the design factors to be considered are outlined to meet the future of rapid POC-based sensors.

Monocrystalline Labeling Enables Stable Plasmonic Enhancement for Isolation-Free Extracellular Vesicle Analysis

Sensitive detection of extracellular vesicles (EVs) as emerging biomarkers has shown great promises for disease diagnosis. Plasmonic metal nanostructures conjugated with molecules that bind specific biomarker targets are widely used for EVs sensing but involve tradeoffs between particle-size-dependent signal intensity and conjugation efficiency. One solution to this problem would be to induce nucleation on nanoparticles that have successfully bound a target biomarker to permit in situ nanoparticle growth for signal amplification, but approaches that are evaluated to date require harsh conditions or lack nucleation specificity, prohibiting their effective use with most biological specimens. This study describes a one-step in situ strategy to induce monocrystalline copper shell growth on gold nanorod probes without decreasing signal by disrupting probe-target interactions or lipid bilayer integrity to enable EV biomarker detections. This approach increases the detected nanoparticle signal about two orders of magnitude after a 10 min copper nanoshell growth reaction. This has significant implications for improved disease detection, as indicated by the ability of a novel immunoassay using this approach to detect low abundance EVs carrying a pathogen-derived biomarker, after their direct capture from serum, to facilitate the diagnosis of tuberculosis cases in a diagnostically challenging pediatric cohort.

Rapid Detection of Lipopolysaccharide and Whole Cells of Francisella tularensis Based on Agglutination of Antibody-Coated Gold Nanoparticles and Colorimetric Registration

The paper presents development and characterization of a new bioanalytical test system for rapid detection of lipopolysaccharide (LPS) and whole cells of Francisella tularensis, a causative agent of tularemia, in water samples. Gold nanoparticles (AuNPs) coated by the obtained anti-LPS monoclonal antibodies were used for the assay. Their contact with antigen in tested samples leads to aggregation with a shift of absorption spectra from red to blue. Photometric measurements at 530 nm indicated the analyte presence. Three preparations of AuNPs with different diameters were compared, and the AuNPs having average diameter of 34 nm were found to be optimal. The assay is implemented in 20 min and is characterized by detection limits equal to 40 ng/mL for LPS and 3 × 10⁴ CFU/mL for whole cells of F. tularensis. Thus, the proposed simple one-step assay integrates sensitivity comparable with other immunoassay of microorganisms and rapidity. Selectivity of the assay for different strains of F. tularensis was tested and the possibility to choose its variants with the use of different antibodies to distinguish virulent and non-virulent strains or to detect both kinds of F. tularensis was found. The test system has been successfully implemented to reveal the analyte in natural and tap water samples without the loss of sensitivity.

Improvement of the signal to noise ratio for fluorescent imaging in microfluidic chips

Microfluidics systems can be fabricated in various ways using original silicon glass systems, with easy Si processing and surface modifications for subsequent applications such as cell seeding and their study. Fluorescent imaging of cells became a standard technique for the investigation of cell behavior. Unfortunately, high sensitivity fluorescent imaging, e.g., using total internal reflection fluorescence (TIRF) microscopy, is problematic in these microfluidic systems because the uneven surfaces of the silicon channels' bottoms affect light penetration through the optical filters. In this work, we study the nature of the phenomenon, finding that the problem can be rectified by using a silicon-on-insulator (SOI) substrate, defining the channel depth by the thickness of the top Si layer, and halting the etching at the buried SiO₂ layer. Then the fluorescent background signal drops by = 5 times, corresponding to the limit of detection drop from = 0.05 mM to = 50 nM of fluorescein. We demonstrate the importance of a flat surface using TIRF-based single-molecule detection, improving the signal to a noise ratio more than 18 times compared to a conventional Si wafer. Overall, using very high-quality SOI substrates pays off, as it improves the fluorescence image quality due to the increase in signal-to-noise ratio. Concerning the cost of microfluidic device fabrication-design, mask fabrication, wafer processing, and device testing-the initial SOI wafer cost is marginal, and using it improves the system performance.

Ultrasmall Pt Nanozymes Immobilized on Spherical Polyelectrolyte Brushes with Robust Peroxidase-like Activity for Highly Sensitive Detection of Cysteine

Distinct platinum (Pt) nanozymes as peroxidase mimics have received extensive interest owing to their outstanding catalytic activity, high environmental tolerance, lower consumption, and great potential in replacing natural enzymes. However, easy agglomeration of Pt nanoparticles (Pt NPs) resulting from the high surface free energy significantly decrease their peroxidase-like activity. Herein, spherical polyelectrolyte brush (SPB)-stabilized ultrasmall Pt NPs (SPB@Pt NPs) were prepared by a novel synthetic strategy where the SPB not only performed as a nanoreactor for the synthesis of ultrasmall Pt NPs but also greatly stabilized Pt NPs against aggregation. The well-defined SPB@Pt NP nanozymes exhibited outstanding peroxidase-like activity for the catalytic oxidation of colorless 3,3',5,5'-tetramethylbenzidine (TMB) to blue oxidized TMB and were then used to establish a colorimetric sensor for rapid detection of cysteine, giving a limit of detection of 0.11 μM. Moreover, the colorimetric detection system was demonstrated with outstanding performance in sensitive and selective detection of cysteine in the presence of several interference molecules. From these results, SPB@Pt NPs have been regarded as promising peroxidase mimics for a large number of applications such as in biosensing, biomedicine, the food industry, and environmental chemistry.

Nanomaterials-enriched sensors for detection of chiral pharmaceuticals

Advancements in nanoscience and nanotechnology have opened new pathways to fabricate novel nanostructures with interesting properties that would be used for different applications. In this respect, nanostructures comprising chirality are one of the most rapidly developing research fields encompassing chemistry, physics and biology. Chirality, also known as mirror asymmetry, describes the geometrical property of an object that is not superimposable on its mirror image. This characteristic plays a crucial role because these identical forms of chiral species in pharmaceuticals or food additives may exhibit different effects on living organisms. Therefore, chiral analysis is an important field of modern chemical analysis in health-related industries that are reliant on the production of enantiomeric compounds involving pharmaceuticals. This review covers the recent advances dealing with the synthesis, design and advantageous analytical performance of nanomaterials-enriched sensors used for chiral pharmaceuticals. We conclude this review with the challenges existing in this research field and our perspectives on some potential strategies with cutting-edge approaches for the rational design of sensors for chiral pharmaceuticals. We expect this comprehensive review will inspire future studies in nanomaterials-enriched chiral sensors.