Fluorometric determination of antioxidant capacity in human plasma by using upconversion nanoparticles and an inner filter effect mechanism

Dual-functional cellulase-mediated gold nanoclusters for ascorbic acid detection and fluorescence bacterial imaging

Protein-protected metal nanomaterials are becoming the most promising fluorescent nanomaterials for biosensing, bioimaging, and therapeutic applications due to their obvious fluorescent molecular properties, favorable biocompatibility and excellent physicochemical properties. Herein, we pioneeringly prepared a cellulase protected fluorescent gold nanoclusters (Cel-Au NCs) exhibiting red fluorescence under the excitation wavelength of 560 nm via a facile and green one-step method. Based on the fluorescence turn-off mechanism, the Cel-Au NCs were used as a biosensor for specificity determination of ascorbic acid (AA) at the emission of 680 nm, which exhibited satisfactory linearity over the range of 10-400 µM and the detection limit of 2.5 µM. Further, the actual sample application of the Au NCs was successfully established by evaluating AA in serum with good recoveries of 98.76%-104.83%. Additionally, the bacteria, including gram-positive bacteria (Bacillus subtilis and Staphylococcus aureus) and gram-negative bacteria (Escherichia coli), were obviously stained by Cel-Au NCs with strong red emission. Thereby, as dual-functional nanoclusters, the prepared Cel-Au NCs have been proven to be an excellent fluorescent bioprobe for the detection of AA and bacterial labeling in medical diagnosis and human health maintenance.

Semiconducting Polymer Nanoparticles-Manganese Based Chemiluminescent Platform for Determining Total Antioxidant Capacity in Diabetic Mice

The total antioxidant capacity (TAC) is a key indicator of the body's resistance to oxidative stress injury in diabetic patients. The measurement of TAC is important for effectively evaluating the redox state to prevent and control the occurrence of diabetes complications. However, there is a lack of a simple, convenient, and reliable method to detect the total antioxidant capacity in diabetes. Herein, we design a novel chemiluminescent platform based on semiconducting polymer nanoparticles-manganese (SPNs-Mn^VII) to detect the total antioxidant capacity of urine in diabetic mice. We synthesize semiconducting polymer nanoparticles with four different structures and discover the ability of Mn^VII to produce singlet oxygen (¹O₂) that is employed to excite thiophene-based SPNs (PFODBT) to emit near-infrared chemiluminescence. Notably, the chemiluminescent intensity has a good linear relationship with the concentration of Mn^VII (detection limit: 2.8 μM). Because antioxidants (e.g., glutathione or ascorbic acid) can react with Mn^VII, such a chemiluminescent tool of SPNs (PFODBT)-Mn^VII can detect the glutathione or ascorbic acid with a larger responsive range. Furthermore, the total antioxidant capacity of urine from mice is evaluated via SPNs (PFODBT)-Mn^VII, and there are statistically significant differences between diabetic and healthy mice. Thus, this new chemiluminescent platform of SPNs (PFODBT)-Mn^VII is convenient, efficient, and sensitive, which is promising for monitoring antioxidant therapy of diabetes.

Exploring the use of upconversion nanoparticles in chemical and biological sensors: from surface modifications to point-of-care devices

Upconversion nanoparticles (UCNPs) have emerged as promising luminescent nanomaterials due to their unique features that allow the overcoming of several problems associated with conventional fluorescent probes. Although UCNPs have been used in a broad range of applications, it is probably in the field of sensing where they best evidence their potential. UCNP-based sensors have been designed with high sensitivity and selectivity, for detection and quantification of multiple analytes ranging from metal ions to biomolecules. In this review, we deeply explore the use of UCNPs in sensing systems emphasizing the most relevant and recent studies on the topic and explaining how these platforms are constructed. Before diving into UCNP-based sensing platforms it is important to understand the unique characteristics of these nanoparticles, why they are attracting so much attention, and the most significant interactions occurring between UCNPs and additional probes. These points are covered over the first two sections of the article and then we explore the types of fluorescent responses, the possible analytes, and the UCNPs' integration with various material types such as gold nanostructures, quantum dots and dyes. All the topics are supported by analysis of recently reported sensors, focusing on how they are built, the materials' interactions, the involved synthesis and functionalization mechanisms, and the conjugation strategies. Finally, we explore the use of UCNPs in paper-based sensors and how these platforms are paving the way for the development of new point-of-care devices.

Upconversion luminescent nanomaterials: A promising new platform for food safety analysis

Foodborne diseases have become a significant threat to public health worldwide. Development of analytical techniques that enable fast and accurate detection of foodborne pathogens is significant for food science and safety research. Assays based on lanthanide (Ln) ion-doped upconversion nanoparticles (UCNPs) show up as a cutting edge platform in biomedical fields because of the superior physicochemical features of UCNPs, including negligible autofluorescence, large signal-to-noise ratio, minimum photodamage to biological samples, high penetration depth, and attractive optical and chemical features. In recent decades, this novel and promising technology has been gradually introduced to food safety research. Herein, we have reviewed the recent progress of Ln³⁺-doped UCNPs in food safety research with emphasis on the following aspects: 1) the upconversion mechanism and detection principles; 2) the history of UCNPs development in analytical chemistry; 3) the in-depth state-of-the-art synthesis strategies, including synthesis protocols for UCNPs, luminescence, structure, morphology, and surface engineering; 4) applications of UCNPs in foodborne pathogens detection, including mycotoxins, heavy metal ions, pesticide residue, antibiotics, estrogen residue, and pathogenic bacteria; and 5) the challenging and future perspectives of using UCNPs in food safety research. Considering the diversity and complexity of the foodborne harmful substances, developing novel detections and quantification techniques and the rigorous investigations about the effect of the harmful substances on human health should be accelerated.

Inner filter effect between upconversion nanoparticles and Fe(ii)-1,10-phenanthroline complex for the detection of Sn(ii) and ascorbic acid (AA)

Dual-function and multi-function sensors can use the same material or detection system to achieve the purpose of detection of two or more substances. Due to their high sensitivity and specificity, dual-function and multi-function sensors have potential applications in many fields. In this article, we designed a dual-function sensor to detect Sn(ii) and ascorbic acid (AA) based on the inner filter effect (IFE) between NaYF₄:Yb,Er@NaYF₄@PAA (UCNPs@PAA) and Fe(ii)–1,10-phenanthroline complex. Fe(ii)–1,10-phenanthroline complex has strong absorption in most of the ultraviolet-visible light range (350 nm–600 nm), and this absorption band overlaps with the green emission peak of UCNPs@PAA at 540 nm; Fe(ii)–1,10-phenanthroline complex can significantly quench the green light emission of UCNPs@PAA. When Sn(ii) or AA is added to the UCNPs@PAA/Fe(iii)/1,10-phenanthroline, they can reduce Fe(iii) to Fe(ii). Fe(ii) can react with 1,10-phenanthroline to form an orange complex, thereby quenching the green light emission of UCNPs@PAA. And the quenching efficiency is related to the concentration of Sn(ii) and AA; there is a linear relationship between quenching efficiency and the concentration of Sn(ii) and AA, within a certain concentration range the detection limits of this dual-function sensor for Sn(ii) and AA are 1.08 μM and 0.97 μM, respectively. In addition, the dual-function sensor can also detect Sn(ii) and AA in tap and spring water.

Based on the inner filter effect (IFE), we use UCNPs to develop a dual-function sensors, which can realize sensitive and selective detection for the Sn(ii) and ascorbic acid (AA).

Optical sensor film for metribuzin pesticide detection

We present a new ratiometric and colorimetric optical sensor film for detection one of the most prevalent pesticide metribuzin. The detection proceeds within the low concentration range between 0 and 1.5 μM. The optical film is based on (a) near infrared (NIR) dye 2-[2-[2-Chloro-3-[2-[1,3-dihydro-3,3-dimethyl-1-(4-sulfobutyl)-2H-indol-2-ylidene]-ethylidene]-1-cyclopen-ten-1-yl]-eth-enyl]-3,3-di-methyl-1-(4-sulfobutyl)-3H-indolium hydroxide and (b) upconverting nanoparticles UCNPs of the NaYF₄:Yb,Er type (diameter ~40-100 nm) that can be emitted a dual (green and red) emission under 980 nm laser diode excitation. Commercially available polyvinyl chloride (PVC) was utilized as a homogeneous matrix for immobilizing NIR dye and UCNPs. The color of the NIR dye in the PVC matrix is based on the concentration of the metribuzin. When the sensor film is exposed to metribuzin the color changes from green to blue with a significant blue shift in the absorption peak (656 nm) of the NIR dye. Furthermore, the quenching of the red emission (659 nm) of the UCNPs is proceeded due to an inner filter effect. Thus, increasing the metribuzin concentration causes the red emission of UCNPs to be reduced. Conversely, the green emission (545 nm) of the UCNPs persists uninfluenced by metribuzin and can act as a reference signal. This optical sensor film provides great sensitivity based on their unique luminescence properties of UCNPs and recognition abilities within a very low detection limit for the metribuzin LOD 6.8 × 10^-8 M with a linear range of 0.23 to 1.5 μM and a relative standard deviation RSD_r (1%, n = 3). The novel optical sensor was applied to the detection of metribuzin in real water samples (surface and ground waters). The sensor film exhibits great selectivity in presence of different types of ions and pesticide molecules. But, atrazine pesticide interferes the analytical signal of the sensor film due to the presence of reactive amino groups in its structure. Memorably, we report the first optical chemical sensor film based on polymer film for metribuzin detection.