A fluorimetric test strip with suppressed "Coffee Ring Effect" for selective mercury ion analysis

Multiwalled Carbon Nanotube-Templated Nickel Porphyrin Covalent Organic Framework for Pencil-Drawn Noninvasive Respiration Sensors

Paper-integrated configuration with miniaturized functionality represents one of the future main green electronics. In this study, a paper-based respiration sensor was prepared using a multiwalled carbon nanotube-templated nickel porphyrin covalent organic framework (MWCNTs@COFNiP-Ph) as an electrical identification component and pencil-drawn graphite electric circuits as interdigitated electrodes (IDEs). The MWCNTs@COFNiP-Ph not only inherited the high gas sensing performance of porphyrin and the aperture induction effect of COFs but also overcame the shielding effect between phases through the MWCNT template. Furthermore, it possessed highly exposed M-N4 metallic active sites and unique periodic porosity, thereby effectively addressing the key technical issue of room-temperature sensing for the respiration sensor. Meanwhile, the introduction of a pencil-drawing approach on common printing papers facilitates the inexpensive and simple manufacturing of the as-fabricated graphite IDE. Based on the above advantages, the MWCNTs@COFNiP-Ph respiration sensor had the characteristics of wide detection range (1-500 ppm), low detection limit (30 ppb), acceptable flexibility for toluene, and rapid response/recovery time (32 s/116 s). These advancements facilitated the integration of the respiration sensor into surgical masks and clothes with maximum functionality at a minimized size and weight. Moreover, the primary internal mechanism of COFNiP-Ph for this efficient toluene detection was investigated through in situ FTIR spectra, thereby directly elucidating that the chemisorption interaction of oxygen modulated the depletion layers, resulting in alterations in sensor resistance upon exposure to the target gas. The encouraging results revealed the feasibility of employing a paper-sensing system as a wearable platform in green electronics.

Mo(IV) Ion-Modulated BSA-Protected Gold Nanocluster Probe for Fluorescence Turn-On Detection of Trimethylamine N-Oxide (TMAO)

Trimethylamine N-oxide (TMAO), a molecule produced by the microbiota, has been associated with human health and illness. Its early discovery in body fluids may affect our understanding of the pathophysiology and treatment of many illnesses. Therefore, our knowledge of the pathophysiology and diagnostics of disorders associated with TMAO might be enhanced by the creation of dependable and fast methods for TMAO detection. Therefore, we developed a fluorescent probe for detecting TMAO utilizing an on-off-on strategy. Bovine serum albumin (BSA)@AuNCs luminescence is effectively quenched by Mo4+ because BSA@AuNCs and Mo4+ have a strong binding relationship. Mo4+ ions can substantially decrease the emission intensity of gold nanoclusters by establishing a BSA@AuNCs-Mo system. Then, the luminescence of BSA@AuNCs was restored due to the interaction between Mo4+ and TMAO. A significant linear relationship was seen between the emission intensity and TMAO concentration within the 0-201 μM range, with a detection limit of 1.532 μM. Additionally, the method can measure TMAO in blood and urine samples.

Development of a highly sensitive fluorescent probe using Delonix regia (Gulmohar) tree pod shell for precise sarcosine detection in human urine samples: advancing prostate cancer diagnosis

We designed a highly sensitive fluorescent sensor for the early detection of sarcosine, a potential biomarker for prostate cancer. This sensor was based on surface-cobalt-doped fluorescent carbon quantum dots (Co-CD) using a FRET-based photoluminescent sensing platform. Blue luminescent carbon quantum dots (CQD) were synthesised through a hydrothermal approach, utilizing Delonix regia tree pod shells. Cobalt was employed to functionalize the CQD, enhancing the quantum-entrapped effects and minimizing surface flaws. To optimize Co-CD preparation, we employed a Box-Behnken design (BBD), and response surface methodology (RSM) based on single-factor experiments. The Co-CD was then used as a fluorescent probe for selective Cu2+ detection, with Cu2+ quenching Co-CD fluorescence through an energy transfer process, referred to as 'turn-off'. When sarcosine was introduced, the fluorescence intensity of Co-CD was restored, creating a 'turn-on' response. The sensor exhibited a Cu2+ detection limit (LOD) of 2.4 µM with a linear range of 0 μM to 10 µM. The sarcosine detection in phosphate buffer saline (PBS, pH 7.4) resulted in an LOD of 1.54 μM and a linear range of 0 to 10 µM. Importantly, the sensor demonstrated its suitability for clinical analysis by detecting sarcosine in human urine. In summary, our rapid and highly sensitive sensor offers a novel approach for the detection of sarcosine in real samples, facilitating early prostate cancer diagnosis.Communicated by Ramaswamy H. Sarma.

A sensitive and facile electrochemical paper-based sensor for glucose detection in whole blood using the Pd/CB-Ni@rGO modified electrode

We created novel Pd/CB-Ni@rGO nanomaterials for glucose detection. The as-synthesized nanomaterials were dropped on the electrode surface using the drop casting technique. The prepared electrode was then attached to a paper-based device containing the sample zone and the reaction zone, enabling plasma isolation and an enzymatic reaction for glucose detection in whole blood. The nanomaterials and surfaces of electrodes were characterized by FTIR, TEM, and SEM. The proposed approach is a disposable glucose detection method that is unaffected by protein fouling on the electrode, and it requires only one drop of human blood. Therefore, there is no need for extensive sample preparation, and there is less sample consumption. Under optimal conditions, Pd/CB-Ni@rGO can accurately measure blood glucose levels with a linear range of 7 to 7140 μM (R2 = 0.9986) and a low detection limit of 0.82 μM. Besides, the developed sensor shows excellent anti-interference capacity, stability, and satisfactory reproducibility and repeatability. Importantly, Pd/CB-Ni@rGO was successfully applied for glucose in whole blood from 4 volunteers, with results that correlated well with those obtained using an Accucheck glucometer at a 95% confidence level. Given its low cost, high accuracy, and ease of use, the blood glucose sensor holds significant potential for clinical use and broadens the area of future noninvasive sensor development.

Fluorescence detection of 4-nitrophenol and α-glucosidase activity based on 4-nitrophenol-regulated fluorescence of silicon nanoparticles

A fluorescence assay for the detection of 4-nitrophenol (4-NP), α-glucosidase (α-Glu) activity and α-Glu inhibitors (AGIs) is developed based on the inner filter effect (IFE), a flexible and simple signal transfer strategy. In this assay, silicon nanoparticles (Si NPs) synthesized under mild and easily accessible conditions are employed as fluorescent indicators. 4-NP efficaciously quenches the fluorescence of Si NPs through the IFE at a very rapid rate, thus achieving 4-NP detection in a mix-to-read manner, which is suitable for on-site detection. The quenching mechanism has been comprehensively studied and confirmed. More significantly, based on the fact that 4-NP can be generated through α-Glu-catalyzed hydrolysis of 4-nitrophenyl-α-D-glucopyranoside (NPG), the fluorescence detection of α-Glu activity is legitimately achieved by employing NPG as the substrate. The linear ranges for 4-NP and α-Glu activity detection are 0.5-60 μM and 0.5-60 mU mL-1 with low detection limits of 0.074 μM and 0.094 mU mL-1, respectively. This method not only can preciously assay targets in real samples, but is also capable of screening AGIs as drugs as well as assessing their inhibition efficiency.

Simultaneous fluorescence sensing of vitamin B2 and sulfur ions based on fluorescent copper nanoparticles

In this study, the F-CuNPs were synthesized by a modified liquid-phase chemical reduction method. Throughout the preparation process, anhydrous copper sulfate was used as the copper source, and ascorbic acid in the NaOH solution served as the reducing and protective agent. Förster resonance energy transfer (FRET) may exist between F-CuNPs and vitamin B2 due to the large spectral overlap between the fluorescence emission spectra of F-CuNPs and the UV-vis absorption spectra of vitamin B2. Therefore, the detection of vitamin B2 was designed based on a FRET system between F-CuNPs and vitamin B2. With S^2- into the F-CuNPs&VB2 system, the fluorescence intensity of vitamin B2 was quenched, while the fluorescence intensity of F-CuNPs was almost unchanged. There may be a specific reaction between S^2- and vitamin B2. Therefore, the research system can be further used to detect S^2- based on ratiometric fluorescent probe. The research findings show that the linear range of vitamin B2 was 0.51 nM-34.64 nM with a detection limit of 0.25 nM (S/N = 3), the linear range of S^2- was 0.64 μM-60.00 μM with a detection limit of 0.32 μM (S/N = 3). Furthermore, the simultaneous fluorescent sensing system has high sensitivity and selectivity. Therefore, this system was designed and successfully used to detect the content of vitamin B2 and S^2- in actual samples to find a new effective method to detect analytes.

A microdots array-based fluoremetric assay with superwettability profile for simultaneous and separate analysis of iron and copper in red wine

A microdots array-based fluoremetric method with superwettability profile has been developed for the simultaneous and separate detection of Fe³⁺ and Cu²⁺ ions in red wine samples. A wettable micropores array was initially designed with high density by using polyacrylic acid (PAA) and hexadecyltrimethoxysilane (HDS), followed by the NaOH etching route. Zinc metal organic frameworks (Zn-MOFs) were fabricated as the fluorescent probes to be immobilized into the micropores array to obtain the fluoremetric microdots array platform. It was found that the fluorescence of Zn-MOFs probes could decrease significantly in the presence of Fe³⁺ and/or Cu²⁺ ions towards their simultaneous analysis. Yet, the specific responses to Fe³⁺ ions could be expected if using histidine to chelate Cu²⁺ ions. Moreover, the developed Zn-MOFs-based microdots array with superwettability profile can enable the accumulation of targeting ions from the complicated samples without any tedious pre-processing. Also, the cross-contamination of different samples droplets can be largely avoided so as to facilitate the analysis of multiple samples. Subsequently, the feasibility of simultaneous and separate detection of Fe³⁺ and Cu²⁺ ions in red wine samples was demonstrated. Such a design of microdots array-based detection platform may promise the wide applications in analyzing Fe³⁺ and/or Cu²⁺ ions in the fields of food safety, environmental monitoring, and medical diseases diagnostics.