Over the last decade, fluorescence has become the dominant tool in biotechnology and medical imaging. These exciting advances have been underpinned by the advances in time-resolved techniques and instrumentation, probe design, chemical / biochemical sensing, coupled with our furthered knowledge in biology. Complementary volumes 9 and 10, Advanced Concepts of Fluorescence Sensing: Small Molecule Sensing and Advanced Concepts of Fluorescence Sensing: Macromolecular Sensing, aim to summarize the current state of the art in fluorescent sensing. For this reason, Drs. Geddes and Lakowicz have invited chapters, encompassing a broad range of fluorescence sensing techniques. Some chapters deal with small molecule sensors, such as for anions, cations, and CO2, while others summarize recent advances in protein-based and macromolecular sensors. The Editors have, however, not included DNA or RNA based sensing in this volume, as this were reviewed in Volume 7 and is to be the subject of a more detailed volume in the near future

This study investigates the photoluminescence (PL), cathodoluminescence (CL), radioluminescence (RL) and ionoluminescence (IL) of natural and synthetic minerals. The natural minerals (fluorapatite, leucophanite, meliphanite and zircon) are mostly from Ilímaussaq Alkaline Complex in South Greenland, Langesundsfjord in Norway and from different localities within Scotland. Synthetic fluorapatite (manufactured as part of the present study) and zircon doped with rare earth elements (REE) were used to compare single and multidoped materials. This study has shown that many of the generally accepted applications of luminescence are not as straightforward as often suggested by the current literature. For example, the study demonstrates how site distribution of REE, based on luminescence, is greatly affected by the dopant level and structural changes, and that different conclusions can be drawn on the same sample depending on method applied. Furthermore, it is clearly demonstrated that using luminescence as a tool for quantitative trace element determination is not going to be a standard technique in the near future if ever. The two main findings supporting this conclusion are the non-linear intensity decrease between different REE activators in the same sample and a large variation between activators at the concentration at which self-quenching starts. In contrast to the general perception that luminescence related to REE is mostly independent of the host, this study has shown a strong interaction between host and REE activators. This conclusion is supported by the change in the activator’s coordination polyhedron observed with single-crystal and powder X-ray diffraction combined with full chemical characterisation. When combining the weak interaction between some REE with the strong host interaction this study has shown the potential for designing new types of colour tuneable and “white light” LEDs based on natural minerals. This study also reveals that zircon doped with Gd³⁺ and Eu³⁺ can potentially have quantum-cutting properties

ABSTRACT The utilization of analytical techniques in deciphering forensic investigation cases represents a significant advancement. Investigators are adept at scrutinizing minute details of evidence, including latent fingerprints, DNA, and bloodstain patterns. Fingerprints stand as paramount biometric evidence for personal identification, widely employed by law enforcement agencies globally due to their uniqueness. This distinct characteristic arises from the presence of various minutiae within the fingerprint patterns, necessitating specialized personnel for meticulous development. Thus, there arises a need for analytical phenomena like luminescence and fluorescence to facilitate the visualization of latent fingerprint patterns (LFPs). Currently, various organic and inorganic fluorescent compounds are used by forensic investigators for fingerprint development. These fluorescent compounds function by binding to specific components within sweat pores located on frictional ridges of fingerprint patterns, thus rendering them visible. This review discusses materials with fluorescence, and additional properties such as aggregation-induced emission (AIE) and highlights the properties, applications, and notable drawbacks of these materials. The primary aim of this review is to spotlight existing techniques, their limitations, and the latest research endeavours in the quest for the most optimal material for fingerprint development. Such material should possess all essential features while minimizing constraints, thereby bolstering forensic investigations on a global scale.

BaClF: Eu 3+ orange‐emitting phosphor was successfully synthesized by a hydrothermal method. The luminescent properties of the material were further enhanced by adding alkali metal ions. XRD analysis confirmed the phase purity and successful synthesis of the BaClF:Eu 3+ , M + phosphor. Under 393‐nm excitation, the fluorescence spectrum of the synthesized product exhibited a main emission peak at 593 nm. Experimental results indicate that the quenching concentration of Eu 3+ ions is 6.0 mol%. To further increase the luminescence intensity, alkali metal ions (Li + , Na + , and K + ) were also introduced as charge compensators. The results showed that Li + was identified as the most effective compensator, yielding a 2.11‐fold enhancement in emission intensity. The optimal doping concentration of Li + was determined to be 6.0 mol%. The internal quantum efficiency (IQE) was theoretically estimated using Judd‐Ofelt parameters, showing a substantial increase upon Li + doping. BaClF: Eu 3+ , Li + phosphor exhibits a color purity as high as 99.6% and a correlated color temperature of 1640.3 K. This indicates that BaClF: Eu 3+ , Li + is a highly promising orange‐emitting phosphor and a candidate material for solid‐state lighting applications.

Circularly polarized luminescence (CPL) of chiral luminescent materials has gained increasing attention because of their significant applications in 3D displays, chiral optoelectronics, anti‐counterfeiting, and encryption. A strongly emissive chiral dye BAcT is synthesized using (R)‐BINOL as the chiral source and a tetraphenylethene group as the fluorophore. Upon the addition of BAcT to the nematic liquid crystal, a left‐handed cholesteric structure is induced. Different concentrations of R/S5011 as chiral co‐dopants are added to prepare a series of structurally colored cholesteric liquid crystal polymer network (CLCN) films. CPL bands are detected for these green emissive CLCN films, and relatively high |glum| values (up to 0.48) are obtained. Furthermore, a fluorescent PMMA‐BAcT layer is prepared by embedding the dye in the PMMA matrix and stacked with a CLCN layer to construct a composite film. Because of the chiral filtering effect of the CLCN film, a high |glum| value up to 1.41 is successfully achieved. Colorful CLCN patterns are prepared, and clear pictures are observed in both reflective and fluorescent modes, contributing to optical anti‐counterfeiting with enhanced security. This work not only provides a deeper understanding of CPL, but also establishes a practical strategy to prepare colorful CLCN patterns for anti‐counterfeiting using inkjet printing technology.

This work was supported by the US National Science Foundation (ECCS- 1101947), National Institutes of Health (P41EB015903, R21EB013761), Department of Defense (FA9550-11-1-0331), and the Korea National Research Foundation (R31-2008-000-10071-0). M.C.G. acknowledges support from the Bullock-Wellman Fellowship, the Daimler and Benz Fellowship and the Marie Curie Career Integration Grant (PCIG12-GA-2012-334407).Bioluminescent organisms are likely to have an evolutionary drive towards high radiance. As such, bio-optimized materials derived from them hold great promise for photonic applications. Here, we show that biologically produced fluorescent proteins retain their high brightness even at the maximum density in solid state through a special molecular structure that provides optimal balance between high protein concentration and low resonance energy transfer self-quenching. Dried films of ​green fluorescent protein show low fluorescence quenching (−7 dB) and support strong optical amplification (gnet=22 cm−1; 96 dB cm−1). Using these properties, we demonstrate vertical cavity surface emitting micro-lasers with low threshold (<100 pJ, outperforming organic semiconductor lasers) and self-assembled all-protein ring lasers. Moreover, solid-state blends of different proteins support efficient Förster resonance energy transfer, with sensitivity to intermolecular distance thus allowing all-optical sensing. The design of fluorescent proteins may be exploited for bio-inspired solid-state luminescent molecules or nanoparticles.Peer reviewe

Bioluminescent organisms, such as fireflies, jellyfish, and glow worms, possess a superb capacity for environment-interactive luminescence, enabling them to adapt to their surroundings. However, developing artificial luminescent materials that mimic the wet, soft, flexible, and multistimuli-responsive nature of bioluminescent organisms remains a challenge. Here, we present a rational design strategy for multistimuli-responsive fluorescent hydrogels in diverse and complex shapes, mimicking the bioluminescent behavior of fireflies. The fluorescence is activated and enhanced by natural and sustainable stimuli─water and temperature─and can be reversibly deactivated on-demand, similar to the role of oxygen and temperature in the firefly bioluminescence. Specifically, the designed molecular additives integrated within the hydrogel matrix increase fluorescence intensity and enhance the reversible and repetitive responsiveness to surrounding solvents without diminishing fluorescence intensity. Moreover, the hydrogel matrix responding to temperature changes enables control of fluorescence. Furthermore, the hydrogel precursor, designed for good printability, allows 3D printing of diverse-shaped fluorescent hydrogel structures, including artificial fluorescent organism models and fluorescence-patterned displays. This capability extends to implementing on-demand dynamic information encryption-decryption display with controllable fluorescent intensity and on-off rates. The proposed design strategy and free-form fabrication of fluorescent hydrogels could provide a viable path toward advanced fluorescent hydrogel development.

The fabrication of materials that can switch between circularly polarized luminescence (CPL) signals is both essential and challenging. Here, two new halogen-bonded fluorescent molecular photoswitches, namely, HB-switch 1 and HB-switch 2, containing α-cyano-substituted diarylethene compounds with different end groups were developed. Upon exposure to specific UV or visible light wavelengths, they exhibited controllable and reversible Z/E photoisomerization. When these switches were integrated into blue-phase liquid crystals (BPLCs), the temperature range of BP significantly expanded. Notably, the BP system incorporating HB-switch 1 exclusively achieved reversible polarization inversion of CPL signals under specific UV/visible light irradiation and during cooling/heating. The photo/thermal dual-response behavior of the CPL signals can be attributed to the phase transition from a high-symmetry 3D BP I lattice to a low-symmetry 1D helical superstructure induced by the Z/E photoisomerization of HB-switch 1 and temperature changes. This study underscores the significance of employing halogen-bond assembly strategies to design materials with switchable CPL signals, opening new possibilities for CPL-active systems.

This thesis describes the development of a microtiter plate assay for determination of uric acid. It also depicts the development, characterization and application of luminescence based optical biosensors for determination of uric acid and glucose. Chapter 1 gives an introduction on the importance of the determination of uric acid and glucose. Furthermore, an overview on the state of the art of optical sensing of oxygen and pH is given, along with a comparison of optical sensor versus electrochemical sensor technology. In this thesis a microtiter plate assay for uric acid determination is described applying an europium complex as fluorescent probe. Hence, the luminescence emission mechanism of lanthanide complexes is explained in detail. Chapter 2 describes a microtiter plate assay for uric acid. The hydrogen peroxide sensitive probe europium(III)-tetracycline (Eu3TC) was applied for sensing hydrogen peroxide that is released by the enzyme uricase during the oxidation of uric acid. Hydrogen peroxide coordinates to Eu3Tc and enhances its luminescence intensity. The assay is carried out in the time-gated mode. Uric acid can be detected in the concentration range up to 60 µM with a limit of detection of 9.9 µM. The assay cannot be applied to the determination of uric acid in urine unfortunately. Urine a complex matrix contains phosphate which quenches the luminescence intensity of the complex Eu3TC-HP strongly. In chapter 3, a biosensor membrane is presented for detection of uric acid. The biosensor membrane consists of a single layer which contains an oxygen probe and the enzyme uricase. The detection of uric acid is based on the measurement of oxygen that is consumed during the oxidation catalyzed by uricase. A ruthenium- or an iridium complex incorporated in organically modified sol-gel is applied as oxygen sensitive probe, whose luminescence intensity is dynamically quenched in presence of oxygen. Uric acid can be detected in the concentration range up to 0.8 mM with a limit of detection of 0.05 mM using the ruthenium complex as oxygen sensitive probe. Applying the iridium complex as oxygen sensitive probe uric acid is detected in the concentration range from 0.02 to 0.6 mM. The optical biosensor using the ruthenium complex as oxygen sensitive probe is successfully applied to the determination of uric acid in blood serum. In chapter 4, a biosensor membrane is prepared for determination of glucose. The fundamental idea of this chapter is the simultaneous detection of glucose via (a) oxygen and (b) pH transduction. The first part of this chapter describes a strategy to embed an oxygen sensitive probe and the enzyme glucose oxidase in a hydrogel matrix and apply it to glucose sensing. The detection scheme is based on the principle described in chapter 3. The enzyme glucose oxidase catalyzes the oxidation of glucose under oxygen consumption which is detected using a ruthenium complex as the oxygen sensitive probe. Its luminescence intensity is enhanced in absence of oxygen. Glucose can be detected in the concentration range from 0.2 to 1.0 mM. In the second part glucose is determined via a pH transducer. During the oxidation of glucose one of the end products is gluconic acid which dissociates in gluconate and protons. Hence, the pH of the microenvironment decreases which can be detected in luminescence changes of a pH sensitive probe. Two pH indicators, HPTS and CF, are applied but without the desirable success. The application of CF as pH indicator is disadvantageous due to strong photobleaching. However, the determination of glucose using HPTS as pH transducer is feasible only in the molar concentration range and the reproducibility of the results is very low. Hence, the simultaneous determination of glucose via oxygen and pH transduction is not possible. In chapter 5, a triple sensor is presented for simultaneous monitoring of glucose via an oxygen and pH transducer along with monitoring the temperature. The oxygen-, pH- and temperature transducers are embedded in a hydrogel matrix along with the enzyme glucose oxidase. The triple sensor is illuminated by one single LED and the resulting emissions of the indicators are imaged by a CCD camera and spectrally separated by using suitable filters. This set up allows the simultaneous monitoring of glucose via oxygen and pH transduction and the temperature. This temperature determination is important because the activity of the enzyme GOx and the luminescence of the oxygen transducer PtTFPL are temperature dependent. Simultaneous sensing of glucose via pH and oxygen transduction along with temperature is successful in the case of monitoring glucose via oxygen transduction along with the temperature. The detection of glucose via pH transduction lacks the desirable success because the response times are very long and the reproducibility of the results is very low

Mechanical response luminescence (MRL) describes the photophysical properties triggered by mechanical stimulation. Usually, MRL can be regulated by intermolecular interactions, molecular conformation or molecular packing, to achieve the desirable optical properties. Herein, at the molecular level, this review covers the factors that influence mechanically responsive fluorescent materials, involving the single- or multifactorial modulation of aliphatic chains, donor-receptor switch, substituent adjustment, and position isomerism. According to these factors, the structure-activity strategies can be summarized as: (i) the self-recovery of optical properties, from the final to initial state, can be regulated by introducing long alkyl chains to a fluorophore. (ii) The sensitivity of MRL materials can be controlled by modifying the donor-acceptor structure via the changed ICT (intramolecular charge transfer) and intramolecular interaction. (iii) The electronic and steric effects of substituents can affect ICT and intermolecular interactions, thereby resulting in high quantum yield and high-contrast MRL materials via changing the molecular stacking of crystalline states. (iv) Intermolecular interaction is modulated by the position isomerism of the substituents, which results in switched molecular packing for the extended response toward a wide range of stimuli. It is anticipated that the molecular mechanisms of these structure-activity relationships will serve as a significant reference for developing novel, high contrast, recyclable mechanical response luminous materials.

Multimodal luminescent materials are widely used in noncontact temperature sensors and fluorescent dynamic anticounterfeiting due to their visible dynamic persistent luminescence and fast optical signal response. To this end, CaY0.99GaO4: 0.01 Bi3+; CaY0.92GaO4: 0.01 Bi3+, 0.07Eu3+; and CaY0.96GaO4: 0.01 Bi3+, 0.03Er3+ phosphors were prepared using the high-temperature solid-state method. The down-conversion luminescence, up-conversion luminescence, long persistent luminescence, and mechanical luminescence of the materials were studied, achieving multicolor luminescence. It was found that the CaY0.92GaO4: 0.01 Bi3+, 0.07Eu3+ phosphor achieves the maximum relative sensitivity of 1.49% K-1. These materials show great potential for applications in anticounterfeiting and optical detection. Through density functional theory and electron localization function analysis, multimodal luminescent materials CaYGaO4: Bi3+, Eu3+/Er3+ were studied. It was found that ion doping leads to a decrease in the band gap and induces the Jahn-Teller effect, creating lower energy channels that accelerate carrier release and enhance optical performance. This is the fundamental reason for the realization of multimodal anticounterfeiting and human motion detection. Subsequently, a novel signal sensing device for human motion detection was developed using the high mechanical luminescence performance of the CaY0.92GaO4: 0.01 Bi3+, 0.07Eu3+ phosphor. The down-conversion luminescence, up-conversion luminescence, long persistent luminescence, and mechanical luminescence properties of CaYGaO4: Bi3+, Eu3+/Er3+ phosphors were demonstrated for multimodal static-dynamic anticounterfeiting applications. Finally, it was demonstrated that the high stability of the wide defect states in CaYGaO4: Bi3+, Eu3+/Er3+ multimodal luminescent materials provide a new approach for temperature sensors, human motion detection, information storage, and anticounterfeiting.

In this work, a methoxy‐modified imidazo‐pyridin–derived fluorescent probe IPOMe‐SF was developed for monitoring sulfite in Chinese medicinal materials, and the imaging in living colorectal cells was conducted. Under the excitation of 355 nm, the response system with IPOMe‐SF exhibited the concentration‐dependent fluorescence enhancement at 490 nm along with the increase of the sulfite level. The response system suggested advantages including a relatively high sensitivity, high stability, rapid response, high selectivity, and low cytotoxicity. The particular privileges associated with the Chinese medicinal materials included the long linear response range and reliable anti‐interference. IPOMe‐SF inferred reliable steadiness for monitoring the sulfite level in the water decoction samples covered the “Zhebawei” herbal series. Further, the imaging system with IPOMe‐SF realized the monitoring of both the exogenous and endogenous sulfite level, as well as the water decoction‐treated status in colorectal cells. This work was meaningful for studying Chinese medicinal materials.

This thesis describes various methods for time-resolved luminescence lifetime determination, and their applications to imaging barometric pressure and temperature. These approaches are superior to luminescence intensity imaging in that they are less influenced by sources of errors like light scattering, inhomogeneous indicator distribution, photobleaching, or background fluorescence because they are intrinsically referenced. The data obtained are precise and unambiguous. Novel sensor materials and methods for time-resolved imaging are described, characterized, and applied. A novel dual pressure-sensitive paint (PSP) and temperature-sensitive paint (TSP) system for time resolved luminescence imaging is introduced, consisting of a platinum porpholactone and a ruthenium-diimine complex,. The dual paint was applied to an aircraft model for wind tunnel testing. The dual paint has proven to be applicable for aerodynamic research. Temperature can be determined with an accuracy of 0.5 K and the surface pressure topology coincides with theory and with the data from conventional pressure measurements. Furthermore, a novel kind of an optical dual sensor is introduced, allowing for signal separation due to different luminescence lifetimes without the need of additional spectral separation. This technique expands the possible spectrum of combination of probes applicable to optical dual sensing. The new sensor system consists of a platinum porphyrin and a europium chelate complex, capable of determining oxygen and temperature simultaneously, without the need for different optical filters. A novel general approach for imaging is presented. It makes use of the fundamental setup of digital cameras and enables to monitor the spectrally resolved luminescence of up to three signals with one single image. The new materials and methods developed during this dissertation led to the fabrication of the first optical triple sensor systems. Two kinds of sensors are reported. They are capable of simultaneously determining the three important analytes pH, T, and O2. The first system consisted of HPTS as the pH-indicator, a Eu-chelate complex as the temperature probe, and a Pt-porpholactone as the probe for oxygen, all encapsulated in appropriate polymer particles. The three signals are separated using optical filters. In the second triple sensor system, the O2 probe of the first system was replaced by a Pt-porphyrin, enabling for time-resolved separation of the temperature signal from the O2 signal. With these new kinds of sensors, it is possible to monitor the three clinically relevant parameters pH, T, and O2 non-invasively, online, and in surpassing spatial resolution. By omitting the oxygen probe, the first temperature compensated optical pH sensor ever described in literature is obtained