Hydroxyapatite nanoparticle based fluorometric turn-on determination of dipicolinic acid, a biomarker of bacterial spores

A length-band fluorescence-based paper analytical device for detecting dipicolinic acid via ofloxacin complexation with Cu2

Dipicolinic acid (DPA) is a key biomarker of bacterial spores. In this study, we present a novel distance-based paper analytical device (d-PAD) for the fluorescence sensing of DPA. The detection mechanism relies on the complexation of ofloxacin (OFL) with Cu2+ ions, where Cu2+ quenches the fluorescence of OFL via static quenching. Upon the introduction of DPA, it interacts with the OFL-Cu2+ complex, resulting in an enhanced fluorescence signal from OFL. The assay demonstrated a limit of detection (LOD) of 0.08 μM over a range of 0.6-120 μM, as measured using a spectrofluorometer. The d-PAD was designed for efficient reagent transport through capillary action on paper substrates, allowing for rapid on-site DPA analysis without requiring advanced laboratory equipment. The length of the fluorescent bands on the d-PADs was proportional to the concentration of DPA, providing a simple and effective readout method. With a sensitivity of 0.6 μM, the device shows a strong response to varying DPA concentrations. This distance-based platform offers a straightforward and quantitative approach to result interpretation, making it a promising tool for detecting bacterial spores in real samples. The development and optimization of this paper-based microfluidic assay represent a significant step forward in portable diagnostic technologies.

Eu-doped ZIF-8 as a ratiometric fluorescence-scattering probe for the anthrax biomarker in food samples based on competitive coordination

Bacillus anthracis spores can cause contagious anthrax, so it is significant for the public safety to detect its biomarker dipicolinic acid (DPA). Ratiometric fluorescent probes for DPA have attracted great interest because of the self-calibration effect, but they suffer from the complicated construction of dual-emitting materials. With combining fluorescence and second-order scattering (SOS), Eu-doped Zn-based metal-organic framework (ZIF-8) was here designed as a ratiometric probe for DPA, avoiding the completed construction of dual-emitting materials. Eu-doped ZIF-8 exhibited no fluorescence but possessed strong SOS ascribed to the nanostructure. However, the competitive coordination of DPA not only triggered the antenna effect of Eu3+ but also caused the decomposition of Eu-doped ZIF-8. As a consequence, the fluorescence enhancement and the SOS weakness were observed upon the addition of DPA to Eu-doped ZIF-8. And thus, a ratiometric probe for DPA was constructed based on Eu-doped ZIF-8 by integrating fluorescence with SOS. The probe as-constructed could quantify DPA in a wide range of 0.1-150 μM with a rapid response (1 min) and a low detection limit (31 nM). It also displayed excellent manifestation for the analysis of food samples with reasonable accuracy (recoveries, 90.0%-101.5%) and satisfactory precision (RSDs, 0.6%-5.7%), offering a reliable tool for the supervision of the public safety.

Self-calibrated HAp:Tb-EDTA paper-based probe with dual emission ratio fluorescence for binary visual and fluorescent detection of anthrax biomarker

Development of the portable device is significant for sensitive and rapid detection of an anthrax biomarker dipicolinic acid (DPA), existing in the B. anthracis. In this work, a novel HAp:Tb-EDTA paper-based ratiometric fluorescent sensor was obtained by a simple one-pot method for rapid and sensitive DPA detection. With the increased DPA concentration, the luminescence intensity of HAp (hydroxyapatite) remained constant, and thus applied as the stable reference signal, while the luminescence signal of Tb3+-EDTA was significantly enhanced due to the antenna effect. Therefore, the HAp:Tb-EDTA paper-based sensor was endowed with self-calibrated and ratiometric fluorescent detection performance for DPA. The proposed sensor showed excellent detection performance with a detection limit as low as 10.8 nM in the linear range of 0.5-30 μM. After combination with a smartphone, rapid visual and fluorescent detection of DPA was achieved. The proposed sensor was successfully applied to detect DPA from B. subtilis spore real samples, showing the application prospects of the paper-based sensors and opening a new horizon to develop novel paper-based point-of-care testing (POCT) devices.

The Detection of Anthrax Biomarker DPA by Ratiometric Fluorescence Probe of Carbon Quantum Dots and Europium Hybrid Material Based on Poly(ionic)- Liquid

Bacillus anthracis has gained international attention as a deadly bacterium and a potentially deadly biological warfare agent. Dipicolinic acid (DPA) is the main component of the protective layer of anthracis spores, and is also an anthrax biomarker. Therefore, it is of great significance to explore an efficient and sensitive DPA detection method. Herein, a novel ratio hybrid probe (CQDs-PIL-Eu3+) was prepared by a simple one-step hydrothermal method using carbon quantum dots (CQDs) as an internal reference fluorescence and a covalent bond between CQDs and Eu3+ by using a polyionic liquid (PIL) as a bridge molecule. The ratiometric fluorescence probe was found to have the characteristics of sensitive fluorescence visual sensing in detecting DPA. The structure and the sensing properties of CQDs-PIL-Eu3+ were investigated in detail. In particular, the fluorescence intensity ratio of Eu3+ to CQDs (I616/I440) was linear with the concentration of DPA in the range of 0-50 μM, so the detection limit of the probe was as low as 32 nm, which was far lower than the DPA dose released by the number of anthrax spores in human body (60 μM) and, thus, can achieve sensitive detection. Therefore, the ratiometric fluorescence probe in this work has the characteristics of strong anti-interference, visual sensing, and high sensitivity, which provides a very promising scheme for the realization of anthrax biomarker DPA detection.

Bacillus spore germination: mechanisms, identification, and antibacterial strategies

Bacterial spores are metabolically inactive and highly resistant to harsh environmental conditions in nature and during decontamination processes in food and related industries. However, inducing germination using specific germinants in dormant spores can convert them into vegetative cells which are metabolically active and fragile. The potential utility of a "germinate to eradicate" strategy, also known as germination-inactivation, has been validated in foods. Meanwhile, the strategy has sparked much interest in triggering and maximizing spore germination. Although many details of the spore germination process have been identified over the past decades, there remain many uncertainties, including some signal transduction mechanisms involved in germination. In addition, the successful implementation of the germination-inactivation strategy relies on the sensitive detection of germinative biomarkers within minutes of germination initiation and the optimal timing for the subsequent inactivation step. Meanwhile, the emergence of biomarkers has renewed attention to the practical application of the spore germination process. Here, this review presents the current knowledge of the germination mechanisms of Bacillus spore, influencing factors, and germination biomarkers. It also covers a detailed discussion on the development of germination-inactivation as a spore eradication strategy.

Lanthanides-Substituted Hydroxyapatite for Biomedical Applications

Lately, there has been an increasing demand for materials that could improve tissue regenerative therapies and provide antimicrobial effects. Similarly, there is a growing need to develop or modify biomaterials for the diagnosis and treatment of different pathologies. In this scenario, hydroxyapatite (HAp) appears as a bioceramic with extended functionalities. Nevertheless, there are certain disadvantages related to the mechanical properties and lack of antimicrobial capacity. To circumvent them, the doping of HAp with a variety of cationic ions is emerging as a good alterative due to the different biological roles of each ion. Among many elements, lanthanides are understudied despite their great potential in the biomedical field. For this reason, the present review focuses on the biological benefits of lanthanides and how their incorporation into HAp can alter its morphology and physical properties. A comprehensive section of the applications of lanthanides-substituted HAp nanoparticles (HAp NPs) is presented to unveil the potential biomedical uses of these systems. Finally, the need to study the tolerable and non-toxic percentages of substitution with these elements is highlighted.

Mechanism insights into bacterial sporulation at natural sphalerite interface with and without light irradiation: The suppressing role in bacterial sporulation by photocatalysis

Unveiling the mechanisms of bacterial sporulation at natural mineral interfaces is crucial to fully understand the interactions of mineral with microorganism in aquatic environment. In this study, the bacterial sporulation mechanisms of Bacillus subtilis (B. subtilis) at natural sphalerite (NS) interface with and without light irradiation were systematically investigated for the first time. Under dark condition, NS was found to inactivate vegetative cells of B. subtilis and promote their sporulation simultaneously. The released Zn2+ from NS was mainly responsible for the bacterial inactivation and sporulation. With light irradiation, the photocatalytic effect from NS could increase the bacterial inactivation efficiency, while the bacterial sporulation efficiency was decreased from 8.1 % to 4.5 %. The photo-generated H2O2 and O2- played the major roles in enhancing bacterial inactivation and suppressing bacterial sporulation process. The intracellular synthesis of dipicolinic acid (DPA) as biomarker for sporulation was promoted by NS in dark, which was suppressed by the photocatalytic effect of NS with light irradiation. The transformation process from vegetative cells to spores was monitored by both 3D-fluerecence EEM and SEM observations. Compared with the NS alone system, the NS/light combined system induced higher level of intracellular ROSs, up-regulated antioxidant enzyme activity and decreased cell metabolism activity, which eventually led to enhanced inactivation of vegetative cells and suppressed bacterial sporulation. These results not only provide in-depth understanding about bacterial sporulation as a new mode of sub-lethal stress response at NS interface, but also shed lights on putting forward suitable strategies for controlling spore-producing bacteria by suppressing their sporulation during water disinfection.

A ratiometric fluorescent sensor made of a terbium coordination polymer for the anthrax biomarker 2,6-dipicolinic acid with on-site detection assisted by a smartphone app

Tb-NDBC is a quantitative ratiometric fluorescence sensor for DPA detection with high sensitivity and selectivity, a rapid response, and durability.

Solid-Supported Amplification of Aggregation Emission: A Tetraphenylethylene-Cucurbit[6]uril@Hydroxyapatite-Based Supramolecular Sensing Assembly for the Detection of Spermine and Spermidine in Human Urine and Blood

The development of sensitive and selective tools for the detection and quantification of biomarkers is important in the diagnosis and treatment of clinical diseases. Spermine (SP) and spermidine (SPD) act as biomarkers for early-stage diagnosis of cancer in humans as their increased levels in urine are indicative of abnormal biological processes associated with this fatal disease. In this study, we introduced a strategy for solid-supported amplification of the effective aggregation-induced-emission (AIE) effect of a water-soluble tetraphenylethylene (TPE)-based probe in developing a supramolecular sensing platform for the rapid, sensitive, and selective detection of SP and SPD in water. The nonemissive TPE derivative (TPEHP) forms a less emissive conjugate with hydroxyl cucurbit[6]uril (CB[6]OH) in water, which undergoes several-fold enhancement of effective emission upon electrostatic interaction with the solid surface of hydroxyapatite nanoparticles (HAp NPs), dispersed in the aqueous media. The corresponding three-component supramolecular assembly disrupts by the intrusion of SP and SPD in the CB[6] portal because of the stronger binding ability with CB[6], resulting in a turn-off fluorescence sensor for SP and SPD with enhanced sensitivity. The assembly-disassembly-based sensing mechanism was thoroughly demonstrated by carrying out isothermal titration calorimetry (ITC), spectroscopic, and microscopic experiments. The sensing system showed low limits of detection (LODs) of 1.4 × 10^-8 and 3.6 × 10^-8 M for SP and SPD, respectively, which are well below the required range for the early diagnosis of cancer. Besides, a good linear relationship was obtained for both SP and SPD. Nominal interference from various metal ions, anions, common chemicals, amino acids, and other biogenic amines makes this sensing platform suitable for the real-time, low-level measurement of spermine (and spermidine) in human urinary and blood samples.

Rare-Earth Eu3+/Gold Nanocluster Ensemble-Based Fluorescent Photoinduced Electron Transfer Sensor for Biomarker Dipicolinic Acid Detection

The use of metal ions to bridge the fluorescent materials to target analytes has been demonstrated to be a promising way to sensor design. Herein, the effect of rare-earth ions on the fluorescence of l-methionine-stabilized gold nanoclusters (Met-AuNCs) was investigated. It was found that europium (Eu³⁺) can significantly suppress the emission of Met-AuNCs, while other rare-earth ions showed a negligible impact. The mechanism on the observed fluorescence quenching of Met-AuNCs triggered by Eu³⁺ was systematically explored, with results revealing the dominant role of photoinduced electron transfer (PET). Eu³⁺ can bind to the surface of Met-AuNCs by the coordination effect and accepts the electron from the excited Met-AuNCs, which results in Met-AuNC fluorescence suppression. After introducing dipicolinic acid (DPA), an excellent biomarker for spore-forming pathogens, Eu³⁺ was removed from the surface of Met-AuNCs owing to the higher binding affinity between Eu³⁺ and DPA. Consequently, an immediate fluorescence recovery occurred when DPA was present in the system. Based on the Met-AuNC/Eu³⁺ ensemble, we then established a simple and sensitive fluorescence strategy for turn-on determination of biomarker DPA, with a linear range of 0.2-4 μM and a low limit of detection of 110 nM. The feasibility of the proposed method was further validated by the quantitative detection of DPA in the soil samples. We believe that this study would significantly facilitate the construction of metal-ion-mediated PET sensors for the measurement of various interested analytes by applying fluorescent AuNCs as detection probes.

Highly stable luminescent europium-doped calcium phosphate nanoparticles for creatinine quantification

The determination of creatinine levels is essential for the detection of renal and muscular dysfunction. Luminescent nanoparticles are emerging as fast, cheap and highly selective sensors for the detection and quantification of creatinine. Nevertheless, current nanosensors only have a short shelf life due to their poor chemical and colloidal stability, which limits their clinical functionality. In this work, we have developed a highly stable, selective and sensitive nanosensor based on europium-doped, amorphous calcium phosphate nanoparticles (Eu-ACP) for the determination of creatinine by luminescence spectroscopy. The colloidal stability of Eu-ACP nanoparticles in aqueous solutions was optimised to ensure a constant signal after up to 4 months in storage. The luminescence intensity of Eu-ACP decreased linearly with the creatinine concentration over the range of 1-120 μM (R² = 0.995). This concentration-response relationship was used to determine creatinine levels in real urine samples resulting in good recovery percentages. Significantly, selectivity assays indicated that none of the potential interfering species provoked discernible changes in the luminescence intensity.

A luminous off-on probe for the determination of 2,6-pyridinedicarboxylic acid as an anthrax biomarker based on water-soluble cadmium sulfide quantum dots

A fluorescence off-on sensing platform was developed based on thioglycolic acid-stabilized cadmium sulfide quantum dots (CdS QDs) as fluorescence probe for the sensitive and selective detection of 2,6-pyridinedicarboxylic acid (DPA) in spores. The fluorescence emission intensity of the quantum dots at 650 nm when excited at 460 nm was first quenched by mixing with europium ions (Eu³⁺) and then recovered after the addition of DPA. The interaction of DPA with Eu³⁺ relieved the quenching effect of Eu³⁺ toward CdS QDs. As the DPA concentration increases, the color of the probe changes from colorless to red. The method exhibits a wide linear range from 1 to 120 μM for DPA determination, with a detection limit of 0.2 μM. The CdS QDs based nanoprobe was successfully applied for sensitive determination of DPA released from bacteria spores. In this case, the detection limit is 3.5 × 10⁴ CFU·mL^-1. Graphical abstract An off-on fluorescence sensor for detecting anthrax markers -2,6-pyridinedicarboxylic acid though restoring the fluorescence of cadmium sulfide quantum dots quenching by europium ions.

Defect-related luminescent nanostructured hydroxyapatite promotes mineralization through both intracellular and extracellular pathways

Hydroxyapatite (HAP) is a widely used biomaterial for bone tissue substitution due to its chemical similarity with the natural bone. Defect-related luminescent HAP materials have the same chemical composition as normal HAP and excellent biocompatibility. However, only few works have focused on the defect-related luminescent HAP materials on bone regeneration. In this work, we systematically investigated the bone regeneration pathway induced by nanostructured particles using defect-related luminescent hydroxyapatite (S2) materials. We monitored the subcellular distribution and location of S2 during osteoblast differentiation with the property of defect-related luminescence. Nano-scale S2 could be internalized by osteoblasts (OBs) via caveolae-mediated endocytosis and macropinocytosis. S2 incorporated into the lysosomes dissolved and released calcium ions for the formation of mineralized nodules. Extracellular S2 also promoted bone regeneration as a nucleation site. Taken together, the physical properties of hydroxyapatite control the bone regeneration pathway in osteoblasts.

Hydroxyapatite (HAP) is a widely used biomaterial for bone tissue substitution due to its chemical similarity with the natural bone.

Electrochemical sensing of L-ascorbic acid by using a glassy carbon electrode modified with a molybdophosphate film

Electrochemical sensing of L-ascorbic acid (AA) is reported based on the use of a redox-active molybdophosphate film on a glassy carbon electrode (GCE). Molybdophosphate is formed by reacting hydroxyapatite nanoparticles with sodium molybdate. The modified GCE can be utilized for detection of AA, typically at a working potential of 0.4 V (vs. Ag/AgCl). The GCE has a decreased overpotential and enhanced sensitivity (219 μA·mM^-1·cm^-2). Response is linear in the 1 μM to 1.5 mM AA concentration range, and the limit of detection is 4 nM. The selectivity of this sensor makes it a useful tool for accurate determination of AA in practical samples as shown for a vitamin C tablet and for spiked beverages. Graphical abstract An electrochemical sensing platform is reported that is based on the use of a redox-active molybdophosphate film that was formed via reacting hydroxyapatite nanoparticles (HAP-NPs) with sodium molybdate. Graphical abstract contains poor quality of text inside the artwork. Please do not re-use the file that we have rejected or attempt to increase its resolution and re-save. It is originally poor, therefore, increasing the resolution will not solve the quality problem. We suggest that you provide us the original format. We prefer replacement figures containing vector/editable objects rather than embedded images. Preferred file formats are eps, ai, tiff and pdf.We have uploaded the graphical abstract as PDF format.

Aptamer based determination of the cancer biomarker HER2 by using phosphate-functionalized MnO2 nanosheets as the electrochemical probe

The authors report a sensitive electrochemical aptamer-based assay for the cancer biomarker human epidermal growth factor receptor-2 (HER2). It is based on the use of MnO₂ nanosheets that were functionalized with phosphate and a HER2 binding aptamer and serve as the electrochemical probe. The assay follows a sandwich protocol. A peptide that can specifically recognize HER2 was immobilized on a gold electrode for the capture of HER2. Then, the functionalized MnO₂ nanosheets were linked to the electrode via the binding between HER2 and HER2 aptamer on the MnO₂ nanosheets. The reaction of phosphate and aptamer on the MnO₂ nanosheets with molybdate leads to the formation of redox-active molybdophosphate. This results in dual signal amplification. The generated electrochemical current was measured at 0.22 V (vs. Ag/AgCl). The assay allows HER2 to be determined in the 0.1 to 500 pg·mL^-1 concentration range, and the detection limit is as low as 0.05 pg·mL^-1. The assay was successfully applied for the detection of HER2 in spiked human serum samples. Graphical abstract Electrochemical detection of breast cancer biomarker human epidermal growth factor receptor-2 (HER2) is reported utilizing phosphate ions and aptamer functionalized MnO₂ nanosheet as probe.