Luminescent Biosensor Research Articles

Measuring IP3 Generation in Real-Time Using a NanoBiT Luminescence Biosensor.

G protein-coupled receptors that activate Gq/11 regulate a range of physiological processes including neurotransmission, energy homeostasis, blood pressure regulation, and calcium homeostasis. Activation of Gq/11-coupled receptors stimulates the generation of inositol 1,4,5-trisphosphate (IP3), which mobilizes intracellular calcium release from the endoplasmic reticulum. This chapter describes an assay that uses a NanoBiT-IP3 luminescent biosensor to detect increases in IP3 in live cells. It describes how to perform these assays to assess signaling by the ghrelin receptor and the calcium-sensing receptor in HEK293 cells.

Biosensing strategies using recombinant luminescent proteins and their use for food and environmental analysis.

Progress in synthetic biology and nanotechnology plays at present a major role in the fabrication of sophisticated and miniaturized analytical devices that provide the means to tackle the need for new tools and methods for environmental and food safety. Significant research efforts have led to biosensing experiments experiencing a remarkable growth with the development and application of recombinant luminescent proteins (RLPs) being at the core of this boost. Integrating RLPs into biosensors has resulted in highly versatile detection platforms. These platforms include luminescent enzyme-linked immunosorbent assays (ELISAs), bioluminescence resonance energy transfer (BRET)-based sensors, and genetically encoded luminescent biosensors. Increased signal-to-noise ratios, rapid response times, and the ability to monitor dynamic biological processes in live cells are advantages inherent to the approaches mentioned above. Furthermore, novel fusion proteins and optimized expression systems to improve their stability, brightness, and spectral properties have enhanced the performance and pertinence of luminescent biosensors in diverse fields. This review highlights recent progress in RLP-based biosensing, showcasing their implementation for monitoring different contaminants commonly found in food and environmental samples. Future perspectives and potential challenges in these two areas of interest are also addressed, providing a comprehensive overview of the current state and a forecast of the biosensing strategies using recombinant luminescent proteins to come.

Nucleic acid-functionalized upconversion luminescence biosensor based on strand displacement-mediated signal amplification for the detection of trivalent chromium ions

BackgroundRapid industrial development has generated serious pollution, including the presence of toxic and harmful heavy metal ions. Among them, trivalent chromium ion (Cr3+) is a very important element that poses a threat to life and health in our industrial wastewater pollution. Thus, it is important to develop efficient fluorescence methods for Cr3+ detection. In this study, an upconversion luminescence biosensor for detecting Cr3+ was constructed based on a DNAzyme, strand displacement reaction (SDR), and DNA-functionalized upconversion nanoparticles (UCNPs). ResultsThe sulfonate-rich poly (sodium 4-styrene sulfonate) (PSS) was modified onto the surface of UCNPs, forming UCNPs@PSS. Then, NH2-Capture probe DNA (NH2-Cp) was further modified onto the UCNPs@PSS surface through sulfonylation, resulting in UCNPs@PSS@NH2-Cp. The DNAzyme activated by Cr3+ triggered the release of the primer probe (Pp), which initiated the SDR system cycle, thereby releasing a tetramethylrhodamine (TAMRA)-modified signal probe (TAMRA-Sp). Finally, UCNPs@PSS@NH2-Cp bound to TAMRA-Sp through complementary base pairing, causing UCNPs and TAMRA to approach each other. Because of the luminescence resonance energy transfer (LRET) mechanism, the upconversion luminescence (UCL) signal of the UCNPs was quenched by TAMRA, enabling the detection of Cr3+ by the change of I585/I545 ratio. This biosensor has good stability, selectivity, and sensitivity, with a linear range of 0.5–75 nM and a detection limit of 0.135 nM for Cr3+. Significance and noveltyFirstly, based on LRET between UCNPs and TAMRA, the quantitative analysis of Cr3+ is achieved through the changes of ratio fluorescence. Secondly, the specificity of the biosensor is improved by utilizing the specific recognition of DNA enzymes. Thirdly, the signal amplification technology of the SDR cycle greatly improves the sensitivity of biosensor. This biosensor will be useful for future environmental safety monitoring and biopsy of biological fluids.

Real-Time Determination of Intracellular cAMP Reveals Functional Coupling of Gs Protein to the Melatonin MT1 Receptor.

Melatonin is a neuroendocrine hormone that regulates the circadian rhythm and many other physiological processes. Its functions are primarily exerted through two subtypes of human melatonin receptors, termed melatonin type-1 (MT1) and type-2 (MT2) receptors. Both MT1 and MT2 receptors are generally classified as Gi-coupled receptors owing to their well-recognized ability to inhibit cAMP accumulation in cells. However, it remains an enigma as to why melatonin stimulates cAMP production in a number of cell types that express the MT1 receptor. To address if MT1 can dually couple to Gs and Gi proteins, we employed a highly sensitive luminescent biosensor (GloSensorTM) to monitor the real-time changes in the intracellular cAMP level in intact live HEK293 cells that express MT1 and/or MT2. Our results demonstrate that the activation of MT1, but not MT2, leads to a robust enhancement on the forskolin-stimulated cAMP formation. In contrast, the activation of either MT1 or MT2 inhibited cAMP synthesis driven by the activation of the Gs-coupled β2-adrenergic receptor, which is consistent with a typical Gi-mediated response. The co-expression of MT1 with Gs enabled melatonin itself to stimulate cAMP production, indicating a productive coupling between MT1 and Gs. The possible existence of a MT1-Gs complex was supported through molecular modeling as the predicted complex exhibited structural and thermodynamic characteristics that are comparable to that of MT1-Gi. Taken together, our data reveal that MT1, but not MT2, can dually couple to Gs and Gi proteins, thereby enabling the bi-directional regulation of adenylyl cyclase to differentially modulate cAMP levels in cells that express different complements of MT1, MT2, and G proteins.

A luminescent sensor for investigating serotonin metabolism in neuroendocrine cancer

BackgroundSerotonin is emerging as a promising therapeutic target in tryptophan hydroxylase 1–positive tumors, but further mechanistic studies are needed to effectively target dysregulated serotonin metabolism. One challenge is a lack of methods for studying the dynamic nature of serotonin metabolism. Here, we report the development of a genetically encoded luminescent biosensor, termed iSero-Rluc, for the real-time detection of serotonin in live cells. MethodsThe engineered serotonin binding domain (iSero) and Renilla luciferase (Rluc) reporter were cloned into yeast and mammalian expression vectors to create a fusion protein that could act as a biosensor to detect endogenous serotonin levels in live cells. The iSero-Rluc biosensor was stably expressed in the BON cell line and luciferase assays, mass spectroscopy, immunofluorescence, and Western blotting were used to study serotonin metabolism under different cell culture conditions. ResultsThe iSero-Rluc sensor detected exogenous serotonin in a yeast model. When stably expressed in the BON cell line, iSero-Rluc revealed that serotonin biosynthesis is increased in an anchorage-independent growth state and is induced upon serum starvation. ConclusionThe iSero-Rluc biosensor is a powerful tool in the study of tumor serotonin metabolism. It enabled real-time detection of alterations in serotonin synthesis in living cells under various growth conditions and has the potential to provide greater insight into serotonin metabolism in different stages of tumor progression and to identify therapeutic strategies to target cancer metastases and carcinoid crises.

The effect of phytochemicals on the signaling molecules of the "Quorum Sensing" system in bacteria

The system of cell–cell communication of bacteria is necessary for bacteria to coordinate interactions between themselves and with higher organisms. It regulates a number of properties of microorganisms, including pathogenicity and resistance to antibiotics. Therefore, the study of methods of influencing this system seems to be critically important. A special place in this context is occupied by plants and their metabolites (phytochemicals), which have the ability to inhibit the system of cell–cell communication in bacterial communities. Studies using bovine ruminal fluid can lead to an understanding of how this process is regulated in the rumen. The aim of the work was to evaluate the possible effect of phytochemicals (trans-cinnamaldehyde, quercetin, coumarin, vanillin) on the signal molecules of the "Quorum sensing" system of bacteria (for example, the recombinant luminescent biosensor Escherichia coli pAL103) in the presence of ruminal fluid of cattle. It was found that the scar fluid at a concentration of 12,5 % did not affect the level of biosensor luminescence. For all studied phytochemicals, the ability to inhibit the process of cell–cell communication (by binding signal molecules) was recorded, which was expressed in a significant decrease in the bioluminescence of the E. coli pAL103 test strain. At the same time, the most pronounced change in the level of biosensor luminescence was detected under the combined action of rumen fluid with trans-cinnamaldehyde, and the smallest change was detected under the influence of ruminal fluid with coumarin, vanillin, or quercetin. The results obtained expand the understanding of the action of phytochemicals, which can be in demand when compiling the diet of cattle and will allow controlling the activity of pathogenic bacteria in animals by suppressing the system of cell–cell communication.

Photorhabdus lux-operon heat shock-like regulation

For decades, transcription of Photorhabdus luminescens lux-operon was considered being constitutive. Therefore, this lux-operon has been used for measurements in non-specific bacterial luminescent biosensors. Here, the expression of Photorhabduslux-operon under high temperature was studied. The expression was researched in the natural strain Photorhabdus temperata and in the heterologous system of Escherichia coli. P. temperata FV2201 bacterium was isolated from soil in the Moscow region (growth optimum 28 °C). We showed that its luminescence significantly increases when the temperature rises to 34 °C. The increase in luminescence is associated with an increase in the transcription of luxCDABE genes, which was confirmed by RT-PCR. The promoter of the lux-operon of the related bacterium P. luminescens ZM1 from the forests of Moldova, being cloned in the heterologous system of E. coli, is activated when the temperature rises from room temperature to 42 °C. When heat shock is caused by ethanol addition, transcription of lux-operon increases only in the natural strain of P. temperata, but not in the heterologous system of E. coli cells. In addition, the activation of the lux-operon of P. luminescens persists in E. coli strains deficient in both the rpoH and rpoE genes. These results indicate the presence of sigma 32 and sigma 24 independent heat-shock-like mechanism of regulation of the lux-operon of P. luminescens in the heterologous E. coli system.

The SpACE-CCM: A facile and versatile cell culture medium-based biosensor for detection of SARS-CoV-2 spike-ACE2 interaction

The COVID-19 pandemic is an ongoing global public health threat. COVID-19 is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, and binding of the SARS-CoV-2 spike to its receptor, angiotensin-converting enzyme 2 (ACE2), on host cells is critical for viral infection. Here, we developed a luminescent biosensor that readily detects interactions of the spike receptor-binding domain (RBD) and ACE2 in cell culture medium (‘SpACE-CCM’), which was based on bimolecular complementation of the split nanoluciferase-fused spike RBD and ectodomain of ACE2 and further engineered to be efficiently secreted from cells by adding a heterologous secretory signal peptide (SSP). Screening of various SSPs identified ‘interferon-α+alanine-aspartate’ as the SSP that induced the highest activity. The SpACE-CCM biosensor was validated by observing a marked reduction of the activity caused by interaction-defective mutations or in the presence of neutralizing antibodies, recombinant decoy proteins, or peptides. Importantly, the SpACE-CCM biosensor responded well in assay-validating conditions compared with conventional cell lysate-based NanoLuc Binary Technology, indicating its advantage. We further demonstrated the biosensor's versatility by quantitatively detecting neutralizing activity in blood samples from COVID-19 patients and vaccinated individuals, discovering a small molecule interfering with the spike RBD-ACE2 interaction through high-throughput screening, and assessing the cross-reactivity of neutralizing antibodies against SARS-CoV-2 variants. Because the SpACE-CCM is a facile and rapid one-step reaction biosensor that aptly recapitulates the native spike-ACE2 interaction, it would be advantageous in many experimental and clinical applications associated with this interaction.

An “off-on” electrochemical luminescence biosensor with aggregation-induced emission for ultrasensitive detection of aflatoxin B1

This work describes a novel “off-on” biosensor for super-sensitive and selective detection of aflatoxin B1 (AFB1). In the biosensor, electrochemiluminescence (ECL) and aggregation-induced emission (AIE) work together to enhance ECL performance by a dibenzo-[b,d]thiophene sulfone-based conjugated microporous polymer, and hairpin DNA1 (H1) and ferrocene (Fc)-apt act as the switches for the "off-on" mode. In the absence of target AFB1, the ECL signal is inhibited because of the steric-hindrance effect, and the biosensor remains in the “off” state. In the presence of AFB1, ECL signal recovery is observed caused by the specific recognition between the AFB1 and Fc-apt, i.e., the biosensor changes to the “on” state. Under optimal experimental conditions, AFB1 can be quantified from 1 pg·mL−1 to 1 μg·mL−1 with an ultralow detection limit of 0.46 pg·mL−1 by the “off-on” biosensor. The biosensor exhibited good practicability for AFB1 assay in corn samples, thus providing a simple and sensitive method for monitoring food safety.

Assessment (in vitro) toxicity of small molecules of plant origin

Small molecules of plant origin can have different effects on bacterial cells. At present, it is of great interest to determine the toxic effects of such compounds in order to assess the potential of their use in veterinary medicine and medicine. The aim of this work was to evaluate the toxicity of various chemically synthesized small molecules of plant origin using a bacterial luminescent biosensor based on Escherichia coli and a cell culture of the freshwater ciliate Stylonychia mytilus. Cinnamic aldehyde had the greatest toxic effect on the E. coli MG1655 pXen7 lux-biosensor, which was expressed in a significant decrease in the luminescence level of the strain compared to the control. Quercetin in the concentration range used did not affect the luminescence intensity of the lux-biosensor. Coumarin and vanillin were characterized by a similar manifestation of the toxic effect. Similar results were also confirmed using S. mytilus as a test object. The results obtained expand the understanding of the possible toxic effect of phytochemicals, which can be used in the development of feed additives in animal husbandry (as analogues of feed antibiotics).

Rapid and ultrasensitive detection of SARS-CoV-2 spike protein based on upconversion luminescence biosensor for COVID-19 point-of-care diagnostics

Here, we firstly introduce a detection system consisting of upconversion nanoparticles (UCNPs) and Au nanorods (AuNRs) for an ultrasensitive, rapid, quantitative and on-site detection of SARS-CoV-2 spike (S) protein based on Förster resonance energy transfer (FRET) effect. Briefly, the UCNPs capture the S protein of lysed SARS-CoV-2 in the swabs and subsequently they are bound with the anti-S antibodies modified AuNRs, resulting in significant nonradiative transitions from UCNPs (donors) to AuNRs (acceptors) at 480 nm and 800 nm, respectively. Notably, the specific recognition and quantitation of S protein can be realized in minutes at 800 nm because of the low autofluorescence and high Yb-Tm energy transfer in upconversion process. Inspiringly, the limit of detection (LOD) of the S protein can reach down to 1.06 fg mL−1, while the recognition of nucleocapsid protein is also comparable with a commercial test kit in a shorter time (only 5 min). The established strategy is technically superior to those reported point-of-care biosensors in terms of detection time, cost, and sensitivity, which paves a new avenue for future on-site rapid viral screening and point-of-care diagnostics.

A Single-Component Luminescent Biosensor for the SARS-CoV-2 Spike Protein.

Many existing protein detection strategies depend on highly functionalized antibody reagents. A simpler and easier to produce class of detection reagent is highly desirable. We designed a single-component, recombinant, luminescent biosensor that can be expressed in laboratory strains of Escherichia coli and Saccharomyces cerevisiae. This biosensor is deployed in multiple homogeneous and immobilized assay formats to detect recombinant SARS-CoV-2 spike antigen and cultured virus. The chemiluminescent signal generated facilitates detection by an unaugmented cell phone camera. Binding-activated tandem split-enzyme (BAT) biosensors may serve as a useful template for diagnostics and reagents that detect SARS-CoV-2 antigens and other proteins of interest.

Stable Cd Metal-Organic Framework as a Multiresponsive Luminescent Biosensor for Rapid, Accurate, and Recyclable Detection of Hippuric Acid, Nucleoside Phosphates, and Fe3+ in Urine and Serum.

Detecting biomarkers associated with diseases has significant meaning for early prevention, diagnosis, and treatment of diseases. The development of luminescent biosensors for rapid and accurate detection in real urine and serum is urgently desired for human health monitoring. Herein, a luminescent cadmium metal-organic framework, {[Cd(L)(bpbix)]·x(solv)}n (1), was successfully prepared by using a urea-functionalized dicarboxylate ligand, 5-(3-(pyridin-4-yl)ureido)isophthalic acid (H2L), 4,4'-bis((1H-imidazol-1-yl)methyl)biphenyl (bpbix), and the Cd2+ ion. The structure of 1 presents a 2-fold interpenetrating three-dimensional pillared-layer framework. The complex 1 exhibits good stability in different-pH aqueous solutions and physiological fluids. Strikingly, the complex 1 shows quick response, high sensitivity, good anti-interference performance, and a recyclable ability for simultaneous sensing of hippuric acid (HA), nucleoside phosphates, and Fe3+ in water. More significantly, this sensor can realize the sensitive and accurate detection of HA, nucleoside phosphates, and Fe3+ in real urine and serum and meet the practical detection needs in clinical diagnosis. These results indicate that the complex 1 as a multiresponsive luminescent biosensor possesses great potential for practical detection of HA, nucleoside phosphates, and Fe3+ in biological samples.

An Overview on Coinage Metal Nanocluster-Based Luminescent Biosensors via Etching Chemistry.

The findings from the synthetic mechanism of metal nanoclusters yield the etching chemistry based on coinage metal nanoclusters. The utilization of such chemistry as a tool that can alter the optical properties of metal nanoclusters has inspired the development of a series of emerging luminescent biosensors. Compared with other sensors, the luminescent biosensors have the advantages of being more sensitive, saving time and saving cost. We reviewed topics on the luminescent sensors based on the etching of emissive coinage metal nanoclusters. The molecules possessing varied etching ability towards metal nanoclusters were categorized with discussions of corresponding etching mechanisms. The understanding of etching mechanisms favored the discussions of how to use etching methods to detecting biochemical molecules. The emerging luminescent biosensors via etching chemistry also provided challenges and new opportunities for analytical chemistry and sensors.

Restoration of the Indicator Properties of Whole-cell Luminescent Biosensors

Whole-cell biosensors are widely used to produce medical diagnostic tests, but in the long term, they tend to lose their indicator properties. Consequently, it is crucial to find ways to restore these properties and prolong the shelf life of the tests. Here, we propose to use electromagnetic radiation with optimally selected parameters of frequency, power, and exposure time. The impact of radiation parameters on biosensor luminescence was studied as well as the effects of different types of radiation coming from laser sources (λ = 875nm), a LED source (λ = 850 ÷ 890nm), and microwave units (at frequencies 42.22, 53.53, 61.18 и 34 ÷ 38GHz). IR treatment resulted in dose-dependent suppression of biosensor luminescence. The luminescence level when exposed to microwave radiation depends on the radiation time and frequency. Also, it has been found that optimal selection of the main radiation parameters enables to restore indicator properties partially lost by biosensors during storage. We explain the mechanism responsible for the sensitizing effect of radiation, which implies the polarization of solvent dipoles and changes in mobility of acceptor molecules. This, in turn, leads to a shift in the chemical equilibrium states and triggers a cascade of biochemical reactions that lead to restoration of the lost indicator properties of biosensors. The study of antagonistic activity has revealed that restored biosensors provide reliable test results after the expiration of their warranty period.

Monte Carlo method for assessment of a multimodal insertable biosensor.

.Significance: Continuous glucose monitors (CGMs) are increasingly utilized as a way to provide healthcare to the over 10% of Americans that have diabetes. Fully insertable and optically transduced biosensors are poised to further improve CGMs by extending the device lifetime and reducing cost. However, optical modeling of light propagation in tissue is necessary to ascertain device performance.Aim: Monte Carlo modeling of photon transport through tissue was used to assess the luminescent output of a fully insertable glucose biosensor that uses a multimodal Förster resonance energy transfer competitive binding assay and a phosphorescence lifetime decay enzymatic assay.Approach: A Monte Carlo simulation framework of biosensor luminescence and tissue autofluorescence was built using MCmatlab. Simulations were first validated against previous research and then applied to predict the response of a biosensor in development.Results: Our results suggest that a diode within the safety standards for light illumination on the skin, with far-red excitation, allows the luminescent biosensor to yield emission strong enough to be detectable by a common photodiode.Conclusions: The computational model showed that the expected fluorescent power output of a near-infrared light actuated barcode was five orders of magnitude greater than a visible spectrum excited counterpart biosensor.

Rational Design of ZIF-8 for Constructing Luminescent Biosensors with Glucose Oxidase and AIE-Type Gold Nanoclusters.

The development of modern technologies has acclimatized biosensors to complicated applicable scenarios with integrated properties as a whole instead of the pursuit of a single-point breakthrough. Here, we targeted a few concerns in the development of enzyme-based biosensors, including stability, analyte enrichment, and signal transduction, and developed a general biosensing model utilizing enzymes, aggregation-induced emission (AIE) luminogens, and stimuli-responsive framework materials as the units. We propose such proof-of-concept of glucose biosensors by coencapsulating glucose oxidase and AIE-type gold nanoclusters into acid-sensitive zeolite imidazolate framework (ZIF)-8 nanocrystals. The acid-activated degradation of ZIF-8 bridges the molecular signals produced by the enzyme-catalytic reaction of glucose and the photon signals generated by ZIF-8-induced AIE effects of gold nanoclusters, resulting in the "turn-off" model nanoprobes for glucose detection with high selectivity. After embedding the nanoprobes into hollow-out tapes, the formed paper biosensors can conveniently detect glucose with the help of a smartphone.

Bacterial luminescent biosensors in the system for assessing the mechanisms of antibacterial activity of carbon-based nanomaterials

The study presents the results of an analysis of possible mechanisms of antibacterial activity of nanocarbon compounds. It was found that the contact of carbon-based nanomaterials with bacterial cells is not accompanied by a violation of their structural integrity and the development of various types of stress (oxidative stress, reaction of the protein-chaperone system, SOS response). The result of this interaction is a change in the magnitude of the surface zeta potential of cells and the permeability of their membrane, which negatively affects the energy processes occurring in target cells. The direct manifestation of this condition is a decrease in the level of luminescence of luminescent strains and a loss of viability.

A stable Cd-MOF as a dual-responsive luminescent biosensor for the determination of urinary diphenyl phosphate and hippuric acid as biomarkers for human triphenyl phosphate and toluene poisoning.

Rapid and accurate determination of biomarkers of human poisoning in real urine is of great significance for the assessment of health status. Herein, a luminescent urea-functionalized metal-organic framework (MOF), {[Cd(L)0.5(bpbix)]·x(solv)}n (1) (H4L = 5,5'-(((naphthalene-1,5-diylbis(azanediyl))bis(carbonyl))bis(azanediyl))diisophthalic acid; bpbix = 4,4'-bis((1H-imidazol-1-yl)methyl)biphenyl), has been successfully synthesized, and exhibits good stability in aqueous solutions in the normal urinary pH range and real urine. Complex 1 can serve as a dual-responsive luminescent biosensor for the detection of diphenyl phosphate (DPP) and hippuric acid (HA) as biomarkers of flame retardant triphenyl phosphate and toluene poisoning, and shows the advantages of high sensitivity, rapid response, good anti-interference capability, and reversibility. More significantly, complex 1 is successfully applied to the sensitive and accurate detection of DPP and HA in real urine with satisfactory recoveries. This work presents a dual-responsive luminescent MOF-based biosensor for simple, rapid, accurate, and reversible determination of urinary DPP and HA, which has promising application potential for the diagnosis of diseases related to triphenyl phosphate and toluene poisoning.

Genetically Encoded Biosensors for the Quantitative Analysis of Auxin Dynamics in Plant Cells.

Plants, as sessile organisms, possess complex and intertwined signaling networks to react and adapt their behavior toward different internal and external stimuli. Due to this high level of complexity, the implementation of quantitative molecular tools in planta remains challenging. Synthetic biology as an ever-growing interdisciplinary field applies basic engineering principles in life sciences. A plethora of synthetic switches, circuits, and even higher order networks has been implemented in different organisms, such as bacteria and mammalian cells, and facilitates the study of signaling and metabolic pathways. However, the application of such tools in plants lags behind, and thus only a few genetically encoded biosensors and switches have been engineered toward the quantitative investigation of plant signaling. Here, we present a protocol for the quantitative analysis of auxin signaling in Arabidopsis thaliana protoplasts. We implemented genetically encoded, ratiometric, degradation-based luminescent biosensors and applied them for studying auxin perception dynamics. For this, we utilized three different Aux/IAAs as sensor modules and analyzed their degradation behavior in response to auxin. Our experimental approach requires simple hardware and experimental reagents and can thus be implemented in every plant-related or cell culture laboratory. The system allows for the analysis of auxin perception and signaling aspects on various levels and can be easily expanded to other hormones, as for example strigolactones. In addition, the modular sensor design enables the implementation of sensor modules in a straightforward and time-saving approach.