Biomarker Of Bacterial Spores Research Articles

A Dual-Mode Fluorescent Nanoprobe for the Detection and Visual Screening of Pathogenic Bacterial Spores.

Bacterial vegetative cells turn into metabolically dormant spores in certain environmental situations. Once suitable conditions trigger the germination of spores belonging to the pathogenic bacterial category, public safety and environmental hygiene will be threatened, and lives will even be endangered when encountering fatal ones. Instant identification of pathogenic bacterial spores remains a challenging task, since most current approaches belonging to complicated biological methods unsuitable for onsite sensing or emerging alternative chemical techniques are still inseparable from professional instruments. Here we developed a polychromatic fluorescent nanoprobe for ratiometric detection and visual inspection of the pathogenic bacterial spore biomarker, dipicolinic acid (DPA), realizing rapidly accurate screening of pathogenic bacterial spores such as Bacillus anthracis spores. The nanoprobe is made of aminoclay-coated silicon nanoparticles and functionalized with europium ions, exhibiting selective and sensitive response toward DPA and Bacillus subtilis spores (simulants for Bacillus anthracis spores) with excellent linearity. The proposed sensing strategy allowing spore determination of as few as 0.3 × 105 CFU/mL within 10 s was further applied to real environmental sample detection with good accuracy and reliability. Visual quantitative determination can be achieved by analyzing the RGB values of the corresponding test solution color via a color recognition APP on a smartphone. Different test samples can be photographed at the same time, hence the efficient accomplishment of examining bulk samples within minutes. Potentially employed in various on-site sensing occasions, this strategy may develop into a powerful means for distinguishing hazardous pathogens to facilitate timely and proper actions of dealing with multifarious security issues.

Fluorescent silica nanoparticles as nano-chemosensors for the sequential detection of Pb2+ ions and bacterial-spore biomarker dipicolinic acid (DPA) in aqueous solution

Herein, we report fluorescein-labelled silica nanoparticles (FSNP) which serve as fluorescent nano-chemosensors for sequential detection of Pb2+ (which is a toxic heavy metal) and dipicolinic acid (DPA) (which is a distinctive indicator biomarker of bacterial spores) with high sensitivity and selectivity. The fluorescence of FSNP is quenched because of the complex formation between Pb2+ ions and surface amide groups, however, the fluorescence is recovered in contact with DPA, resulting from the association of DPA with surface bound Pb2+ ions. FSNP-Pb2+ complexes show high sensitivity towards DPA with a low detection limit of 850 nM which is approximately seventy times lower than the infectious dosage of bacterial spores (60 μM). Lateral flow test platform was further developed to show the applicability and practicability of our system.

Zirconium-Directed Supramolecular Self-Assembly of Coenzyme A@GNCs with Enhanced Phosphorescence for Developing Ultrasensitive Tracer Probe of Dipicolinic Acid, a Biomarker of Bacterial Spores.

Luminescent gold nanoclusters (GNCs) are a class of attractive quantum-sized nanomaterials bridging the gap between organogold complexes and gold nanocrystals. They typically have a core-shell structure consisting of a Au(I)-organoligand shell-encapsulated few-atom Au(0) core. Their luminescent properties are greatly affected by their Au(I)-organoligand shell, which also supports the aggregation-induced emission (AIE) effect. However, so far, the luminescent Au nanoclusters encapsulated with the organoligands containing phosphoryl moiety have rarely been reported, not to mention their AIE. In this study, coenzyme A (CoA), an adenosine diphosphate (ADP) analogue that is composed of a bulky 5-phosphoribonucleotide adenosine moiety connected to a long branch of vitamin B5 (pantetheine) via a diphosphate ester linkage and ubiquitous in all living organisms, has been used to synthesize phosphorescent GNCs for the first time. Interestingly, the synthesized phosphorescent CoA@GNCs could be further induced to generate AIE via the PO32- and Zr4+ interactions, and the observed AIE was found to be highly specific to Zr4+ ions. In addition, the enhanced phosphorescent emission could be quickly turned down by dipicolinic acid (DPA), a universal and specific component and also a biomarker of bacterial spores. Therefore, a Zr4+-CoA@GNCs-based DPA biosensor for quick, facile, and highly sensitive detection of possible spore contamination has been developed, showing a linear concentration range from 0.5 to 20 μM with a limit of detection of 10 nM. This study has demonstrated a promising future for various organic molecules containing phosphoryl moiety for the preparation of AIE-active metal nanoclusters.

Highly selective and multicolor ultrasensitive assay of dipicolinic acid: The integration of terbium(III) and gold nanocluster

A novel multicolor fluorescent nano-probe based on the hybridization of Tb3+ ion with gold nanoclusters (Au NCs) was synthesized to monitor and on-site visual assay of 2,6-pyridinedicarboxylic acid (DPA), a biomarker of bacterial spores. DPA can replace the water molecule in the center of Tb3+ and strongly coordinate with Tb3+ based on the analyte-triggered antenna effect. Simultaneously, the red fluorescence of Au NCs is not influenced after addition of DPA and can be used as steady inside fluorescence reference channel to measure background noise. On this basis, the multicolor fluorescence nano-probe based on Tb3+-doped Au NCs for fast analysis of DPA was fabricated. The linear range of this method is 0 to 12.5 μM and the limit of detection is 3.4 nM, which is well below the quantity of DPA concentration of 60 μM released by the spore transmission dose of anthrax infection. The proposed multicolor fluorescence nano-probe was successfully detecting DPA in actual sample with good sensitivity and specificity. In addition, the visual paper-based nano-probe is designed to detect DPA by using the color scanning application of smart phone. This developed platform possesses abroad application prospects with advantages of effective, convenient carrying, simple operation, good selectivity and repeatability.

Stimulus response of HNT-CDs-Eu nano-sensor: Toward visual point-of-care monitoring of a bacterial spore biomarker with hypersensitive multi-color agarose gel based analytical device

Ultrasensitive visual detection of anthrax markers is of great significance for disease prevention and early warning of terrorist attacks. A novel of dual-emission ratiometric fluorescent nano-probe (HNT-CDs-Eu) has been elaborately tailored based on the direct in-situ growth of CDs on natural mineral nanotubes (HNTs) for the determination and visual assay of DPA concentrations, using DTPA as the efficient chelating agent and the raw material for the preparation of CDs. The rich carboxyl groups of DTPA also provide coordination sites for Eu3+ to form highly sensitive recognition groups. This multi-color nano-sensor can not only realize ultra-sensitive trace detection of pure DPA, but also meet the feasibility of visual sensing of DPA in environmental water samples. Since the common filter paper has strong blue fluorescence under ultraviolet light irradiation at 365 nm, a color agarose gel for visual inspection and an advanced analytical device for one-to-two decoder are further prepared to realize the intelligent and real-time detection of DPA.

Fluorescent detection of dipicolinic acid as a biomarker in bacterial spores employing terbium ion-coordinated magnetite nanoparticles

Anthrax is a bioterror agent because of its toxicity and the tolerance of its bacterial spores. Thus, researchers have attempted to develop various nanomaterials to detect dipicolinic acid (DPA), a biomarker of bacterial spores. Nanomaterials containing lanthanide ions have received considerable attention, owing to their potential to exhibit high sensitivity and selectivity in the detection of DPA via chelation with molecules. However, the fluorescent signals of the lanthanide complex are quenchable because the nanomaterials simultaneously absorb the excitation and emission light. For the precise detection of DPA, pure signals have to be obtained from the complex by alleviating the quenching effect of the nanomaterials. In this study, we develop a structure with terbium ion (Tb3+)-coordinated magnetite (Fe3O4) nanoparticle to detect DPA. Tb3+ can be detached from the magnetite during chelation with the DPA, and the complex can emit the unencumbered signals with improved detection limit through the application of a magnetic field. The detection system exhibits a significantly lower detection limit (5.4 nM) than the infectious dosage of anthrax (60 μM) with high selectivity and chemical stability. This study informs the improvement of detection limits via the separation of nanomaterials and lanthanide complex.

Ultra-sensitive reusable SERS sensor for multiple hazardous materials detection on single platform

We demonstrate the detection of dipicolinic acid, (DPA), a biomarker of bacterial spores for Bacillus anthracis, 2,4-Dinitrotoluene (DNT) and picric acid (PA) nitroaromatic hazardous chemicals on ultra-sensitive, reusable femtosecond laser textured Au nanostructures decorated with hierarchical AuNPs as a SERS substrate. The AuNPs were achieved by ablating an Au sheet using two different laser scan speeds (1 and 0.1 mm/s) in linear and crossed patterns. The morphological studies revealed dense hierarchical nanostructures decorated with spherical AuNPs possessing 30–40 nm in size in 0.1 mm/s laser scan. The limits of detection (LOD) of the sensor were determined from the detailed SERS measurements and were estimated to be 0.83 pg/L, 3.6 pg/L and 2.3 pg/L for DPA, DNT, and PA, respectively. To the best of our knowledge, the achieved sensitivity is nearly 2 orders improved for DPA when compared with the currently reported LODs using other techniques and 1 order in the case of SERS. Moreover, for DNT and PA the LODs were found to be either superior or comparable with recent reports. We have also demonstrated the competence of our SERS substrates by testing a few real samples (water spiked with these analytes) and again obtained very good sensitivity.

A smartphone-integrated multicolor fluorescence probe of bacterial spore biomarker: The combination of natural clay material and metal-organic frameworks

The metal-organic frameworks (MOFs) functionalized palygorskite (Pal) hybrid as a novel multicolor fluorescence probe for the detection of bacterial spore biomarker-dipicolinic acid (DPA), had been prepared via in-situ growth. The MOFs can effectively encapsulate dye molecules on the surface of Pal, and the rich carboxyl groups on its surface can coordinate with europium ions (Eu3+), forming a highly sensitive recognition group. The results indicated that the limit of detection (LOD) of this multicolor fluorescence probe was as low as 9.3 nM and was obviously lower than the amount of anthrax spores infecting the human body (60 μM). Moreover, a wide linear range from 0 to 35 μM was obtained. The high specific surface area of Pal, as well as the permanent porosity and suitable binding sites of Eu3+-doped MOFs may play a major role in the sensitivity and linear detection range. The multicolor fluorescence strategy made full use of the diversity of fluorescence signals collected by dye molecules and lanthanide ions, which can realize the real-time and on-site detection through the smartphone with a color-scanning application (APP). The practicability of this probe was further verified by detecting DPA released by non-infectious Bacillus subtilis.

Tb(iii)-doped nanosheets as a fluorescent probe for the detection of dipicolinic acid.

A new fluorescent probe based on terbium(iii)-doped nanosheets was designed for detecting low-levels of dipicolinic acid (DPA), a biomarker of bacterial spores. The ability to detect ultra-low concentrations of DPA is therefore of great significance. First, Tb(iii)-doped ytterbium hydroxide nanosheets were obtained by mechanical exfoliation from layered rare-earth hydroxide (LRH) materials. The morphology of the as-synthesized nanosheets was studied by transmission electron microscopy and atomic force microscopy. The Tb(iii)-doped nanosheets are demonstrated to be highly sensitive to DPA, which remarkably enhances Tb(iii) luminescence intensities at a wavelength of 544 nm. Furthermore, Tb(iii) emission increases linearly with DPA concentration. Selectivity studies were conducted by adding different competing aromatic ligands to the sensing solution; however, their fluorescence responses were observed to be negligibly small in comparison with that of DPA. Our findings provide a basis for the application of Tb(iii)-doped nanosheets for accurate, sensitive, and selective monitoring of DPA as a biomarker of anthrax.

GdPO4-Based Nanoprobe for Bioimaging and Selective Recognition of Dipicolinic Acid and Cysteine by a Sensing Ensemble Approach.

Multiple functions incorporated in one single-component nanoplatform pave the way for important biomedicine applications. Herein, a multifunctional terbium-doped gadolinium orthophosphate (GdPO4:Tb-EDTA) nanoplatform was prepared through a simple, ecofriendly, one-step hydrothermal method. Results showed that dipicolinic acid (DPA), the biomarker of bacterial spores, significantly increased the fluorescence intensity of this nanoplatform and conferred it with rapid response and excellent selectivity. Subsequently, the fluorescence of the ensemble GdPO4:Tb-EDTA-DPA can be remarkably quenched by Cu2+, which led to a rewritable nanosensor used in the detection of cysteine (Cys) with excellent sensitivity. In addition, GdPO4:Tb-EDTA can also be a potential T1-weighted magnetic resonance imaging (MRI) contrast agent, which indicated a satisfactory in vitro MRI with r1 relaxivity values of 13.9 mM-1 s-1 and in vivo MRI through intravenous administration on a rat model. Overall, the proposed assay may have great theoretical and practical significance for designing multifunctional biomaterials.

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

Hydroxyapatite nanoparticles (HAP-NPs) were rendered fluorescence by doping with Eu(III) ion. The resulting fluorescent NPs are shown to be viable probes for sensitive and selective determination of dipicolinic acid (DPA), a major constituent of bacterial spores as used in bioterrorism. It is found that the addition of DPA to solutions of such HAP-NPs result in an enhancement of fluorescence due to the coordination of DPA with the Eu(III) dopant. The assay allows DPA to be detected in the 0.1 to 40μM concentration range and with a 77nM detection limit. The assay was applied to the detection of spores of Bacillus subtilis. The attractive properties of the probe make it a promising candidate for used in rapid detection of pathogenic bacterial spores. Graphical abstract Fluorescent hydroxyapatite nanoparticles (HAP-NPs) are shown to be a viable probe for detection of dipicolinic acid, a major constituent of bacterial spores. The red asterisks represent the fluorescence intensity of the HAP-NPs.

Three-Dimensional Plasmonic Trap Array for Ultrasensitive Surface-Enhanced Raman Scattering Analysis of Single Cells.

Single-cell analysis provides an important strategy to evaluate cellular heterogeneity. Although surface-enhanced Raman scattering (SERS) has been considered as a promising label-free technique for single-cell analysis, it remains at the early stage for characterizing the extracellular metabolites of single cells. Herein, we developed a convenient, flexible, and straightforward three-dimensional (3D) plasmonic trap array for simultaneously compartmentalizing and sensitively detecting single-cell metabolites. The 3D trap was spontaneously self-formed by an interfacial-energy-driven process when a liquid droplet was covered with an immiscible oil liquid (polydimethylsiloxane, PDMS). When a droplet of pure AgNO3 solution was immersed into PDMS, Ag+ ions were automatically reduced by the residual Si-H groups in PDMS. Snowflake-like nanoparticles of Ag could be formed on the inner surface of the 3D traps by tuning the concentration of Ag salt precursors and then assembled to flower-like microstructures, endowing the traps with remarkable plasmon enhancement. The established 3D traps exhibited considerably enhanced surface plasmon resonance signals for Raman reporting, and a low detection limit at the aM level was achieved for p-aminothiophenol. Moreover, these 3D traps can serve as an efficient tool for single-cell SERS measurement. As a proof-of-concept, dipicolinic acid, a common biomarker of bacterial spores, was successfully detected from a single cell. The presented approach provides a versatile tool for label-free and sensitive detection of single-cell environments.

Eriochrome Black T-Eu3+ Complex as a Ratiometric Colorimetric and Fluorescent Probe for the Detection of Dipicolinic Acid, a Biomarker of Bacterial Spores.

A novel ratiometric colorimetric and fluorescent dual probe based on Eriochrome Black T (EBT)-Eu3+ complex was designed to detect dipicolinic acid (DPA), a major constituent of bacterial spores, with high sensitivity and selectivity. UV-vis titration experiments demonstrated that EBT and Eu3+ ions formed a 1:1 coordination pair in water. In the presence of Eu3+ ions, the blue solution of EBT changed to magenta, however, upon the addition of DPA, the magenta color changed to blue immediately and characteristic fluorescence emission from DPA-Eu3+ complex was observed. In addition, the sensitivity of the system was further evaluated on Geobacillus stearothermophilus spores and as low as 2.5 × 105 spores were detected.

Environmentally Safe Mercury(II) Ions Aided Zero-Background and Ultrasensitive SERS Detection of Dipicolinic Acid.

Field, reliable, and ultrasensitive detection of dipicolinic acid (DPA), a general biomarker of bacterial spores and especially Bacillus anthracis, is highly desirable but still challenging in current biometric security emergency response system. Herein we report an environmentally safe mercury(II) ions-mediated and competitive coordination interaction based approach for rationally designed surface-enhanced Raman scattering (SERS)-active gold nanoparticles (AuNPs), enabling rapid, ultrasensitive and zero-background detection of DPA without the pretreatment of samples. By means of competitiveness, these papain-capped gold nanoparticles (P-AuNPs) are induced to undergo controllable aggregation upon the addition of Hg2+ ions and DPA with a concentration range (1 nM∼8 μM), which correspondingly cause quantitative changes of SERS intensity of cresyl violet acetate (CVa) conjugated AuNPs. The decreased Raman intensity obtained by subtracting two cases of additives that contain only Hg2+ and the mixture of Hg2+ and DPA is proportional to the concentration of DPA over a range of 1 nM∼8 μM (R2 = 0.9824), with by far the lowest limit of detection (LOD) of 67.25 pM (0.01 ppb, S/N = 3:1). Of particular significance, mercury(II) ions actually play two roles in the process of measurements: a mediator for two designed competitive ligands (DPA and papain), and also a scavenger for the possibly blended ligands due to the different interaction time between DPA and the interferent with Hg2+ ions, which guarantees the interference-free detection of DPA even under real conditions.

A ratiometric nanosensor based on lanthanide-functionalized attapulgite nanoparticle for rapid and sensitive detection of bacterial spore biomarker

Since the 2001 anthrax attacks, researchers have focused on the development of a bacterial spore biomarker detector with rapid response time and high sensitivity and selectivity. Hence, a ratiometric fluorescent nanosensor based on lanthanide-functionalized attapulgite (Atta) was designed and prepared using dye-doped Atta as an internal reference. Atta, which is famous because of Maya Blue, is a hydrated magnesium aluminum silicate present in nature, with pronounced adsorption and a large specific surface area rich in silicon hydroxyl. The adsorption of dye molecules benefits the formation of an internal reference with orange fluorescence. Meanwhile, silicon hydroxyl would be available for terbium (Tb3+) complex grafting, which favors the sensitization of the bacterial spore biomarker. With increasing dipicolinic acid (DPA) concentrations, energy transfer from DPA to Tb3+ gradually enhanced, thereby resulting in strong and predominant green fluorescence. The ratiometric fluorescence intensity is highly sensitive. It has a limit of detection of 9.8 nM, which is much lower than the infectious dosage of Bacillus anthracis spores (60 μM) for humans. The rapid response time (10s), high selectivity, and reliable and practical performances in actual applications make this ratiometric fluorescent nanosensor useful in the detection of biomarkers for various bacterial spores. Moreover, the reported construction of visual ratiometric detection system follows the sustainable development idea of ‘‘from nature, for nature, into the nature’’ and promotes the use of naturally renewable resources to produce promising and eco-friendly functional materials for various applications.

Fluorescent detection of dipicolinic acid as a biomarker of bacterial spores using lanthanide-chelated gold nanoparticles

Gold nanoparticles (GNPs) functionalized with ethylenediamine-lanthanide complexes (Eu-GNPs and Tb-GNPs) were used for the selective fluorescent detection of dipicolinic acid (DPA), a unique biomarker of bacterial spores, in water. Particles were characterized by transmission electron microscopy and zeta potential measurements. The coordination of DPA to the lanthanides resulted in the enhancement of the fluorescence. A selective response to DPA was observed over the nonselective binding of aromatic ligands. The ligand displacement strategy were also employed for the ratiometric fluorescent detection of DPA. 4,4,4-trifluoro-1-(2-naphthyl)-1,3-butanedion (TFNB) was chosen as an antenna to synthesize ternary complexes. The addition of DPA on EuGNP:TFNB ternary complex quenched the initial emission of the complex at 615nm and increased the TFNB emission at 450nm when excited at 350nm. The results demonstrated that the ratiometric fluorescent detection of DPA was achieved by ligand displacement strategy.

Facile ratiometric fluorapatite nanoprobes for rapid and sensitive bacterial spore biomarker detection

Since bacterial spores, such as Bacillus anthracis spores, are extremely hazardous to human beings and animals, efforts have focused on the development of bacterial spore detector with rapid response and high selectivity and sensitivity. Therefore, we reported a facile one-step chelating-reagent-assisted hydrothermal synthesis of lanthanide-doped fluorapatite (FA) nanoprobes for detecting the biomarker of bacterial spores. In FA synthesis, ethylenediaminetetraacetic acid (EDTA) can serve not only as a shape controller and a stabilizer but also as a chelating reagent for lanthanide ions. After the fabrication, terbium (or europium) ions were not only embedded into lattice models of FA nanocrystals, but also chelated by EDTA on the surface of the FA nanocrystals, which can be available for detecting the biomarker (i.e., dipicolinic acid) of bacterial spores. The obtained FA: Ln–EDTA nanoprobes can provide reference fluorescence which play crucial roles in the calibration and correction of concentration. The fluorescence intensities of FA: Tb–EDTA or FA: Eu–EDTA from Tb3+ or Eu3+ emission were highly sensitive and increased gradually with increasing DPA concentrations. The limit of detection of FA: Tb–EDTA was 8.2nM, which is lower than that of FA: Eu–EDTA (20.9nM). It can be attributed to the fact that DPA can achieve a more effective energy transfer to Tb3+ than to Eu3+. Additionally, the nanoprobes were successfully applied for the determination of DPA in fetal calf serum samples. Given their rapid response and high sensitivity and selectivity, these ratiometric fluorescent nanoprobes are promising tools for the detection of bacterial spores.

Ratiometric Luminescent Detection of Bacterial Spores with Terbium Chelated Semiconducting Polymer Dots

We report a ratiometric fluorescent sensor based on semiconducting polymer dots chelated with terbium ions to detect bacterial spores in aqueous solution. Fluorescent polyfluorene (PFO) dots serve as a scaffold to coordinate with lanthanide ions that can be sensitized by calcium dipicolinate (CaDPA), an important biomarker of bacterial spores. The absorption band of PFO dots extends to deep UV region, allowing both the reference and the sensitizer can be excited with a single wavelength (~275 nm). The fluorescence of PFO remains constant as a reference, while the Tb(3+) ions exhibit enhanced luminescence upon binding with DPA. The sharp fluorescence peaks of β-phase PFO dots and the narrow-band emissions of Tb(3+) ions enable ratiometric and sensitive CaDPA detection with a linear response over nanomolar concentration and a detection limit of ~0.2 nM. The Pdots based sensor also show excellent selectivity to CaDPA over other aromatic ligands. Our results indicate that the Tb(3+) chelated Pdots sensor is promising for sensitive and rapid detection of bacterial spores.

Enhancement of Anion Binding in Lanthanide Optical Sensors

In the design of molecular sensors, researchers exploit binding interactions that are usually defined in terms of topology and charge complementarity. The formation of complementary arrays of highly cooperative, noncovalent bonding networks facilitates protein-ligand binding, leading to motifs such as the "lock-and-key". Synthetic molecular sensors often employ metal complexes as key design elements as a way to construct a binding site with the desired shape and charge to achieve target selectivity. In transition metal complexes, coordination number, structure and ligand dynamics are governed primarily by a combination of inner-sphere covalent and outer-sphere noncovalent interactions. These interactions provide a rich variable space that researchers can use to tune structure, stability, and dynamics. In contrast, lanthanide(III)-ligand complex formation and ligand-exchange dynamics are dominated by reversible electrostatic and steric interactions, because the unfilled f shell is shielded by the larger, filled d shell. Luminescent lanthanides such as terbium, europium, dysprosium, and samarium display many photophysical properties that make them excellent candidates for molecular sensor applications. Complexes of lanthanide ions act as receptors that exhibit a detectable change in metal-based luminescence upon binding of an anion. In our work on sensors for detection of dipicolinate, the unique biomarker of bacterial spores, we discovered that the incorporation of an ancillary ligand (AL) can enhance binding constants of target anions to lanthanide ions by as much as two orders of magnitude. In this Account, we show that selected ALs in lanthanide/anion systems greatly improve sensor performance for medical, planetary science, and biodefense applications. We suggest that the observed anion binding enhancement could result from an AL-induced increase in positive charge at the lanthanide ion binding site. This effect depends on lanthanide polarizability, which can be established from the ionization energy of Ln(3+) → Ln(4+). These results account for the order Tb(3+) > Dy(3+) > Eu(3+) ≈ Sm(3+). As with many lanthanide properties, ranging from hydration enthalpy to vaporization energy, this AL-induced enhancement shows a large discrepancy between Tb(3+) and Eu(3+) despite their similarity in size, a phenomenon known as the "gadolinium break". This discrepancy, based on the unusual stabilities of the Eu(2+) and Tb(4+) oxidation states, results from the half-shell effect, as both of these ions have half-filled 4f-shells. The high polarizability of Tb(3+) explains the extraordinarily large increase in the binding affinity of anions for terbium compared to other lanthanides. We recommend that researchers consider this AL-induced enhancement when designing lanthanide-macrocycle optical sensors. Ancillary ligands also can reduce the impact of interfering species such as phosphate commonly found in environmental and physiological samples.

Dual colorimetric and luminescent assay for dipicolinate, a biomarker of bacterial spores

A binary mixture of Tb(3+) and pyrocatechol violet (PV) forms a 1 : 1 Tb(3+)/PV complex that can be used in a dye displacement assay. Addition of dipicolinate (DPA) to the Tb(3+)/DPA complex simultaneously produces a PV color change from blue to yellow and luminescence emission from the newly formed Tb(3+)/DPA complex.