Ultrasensitive On-Field Luminescence Detection Using a Low-Cost Silicon Photomultiplier Device

Cosmo ArduSiPM: An All-in-One Scintillation-Based Particle Detector for Earth and Space Application

Thanks to advancements in silicon photomultiplier sensors (SiPMs) and system-on-chip (SoC) technology, our INFN Roma1 group developed ArduSiPM in 2012, the first all-in-one scintillator particle detector in the literature. It used a custom Arduino Due shield to process fast signals, utilizing the Microchip Sam3X8E SoC's internal peripherals to control and acquire SiPM signals. The availability of radiation-tolerant SoCs, combined with the goal of reducing system space and weight, led to the development of an innovative second-generation board, a better-performing device called Cosmo ArduSiPM, suitable for space missions. The architecture of the new detector is based on the Microchip SAMV71 300 MHz, 32-bit ARM® Cortex®-M7 (Microchip Technology Inc., Chandler, AZ, USA). While the analog front-end is essentially identical to the ArduSiPM, it utilizes components with the smallest possible package. The board fits in a CubeSat module. Thanks to the compact design, the board has two independent channels, with a total weight of only 40 grams within a CubeSat form factor. The ArduSiPM architecture is based on a single microcontroller and fast discrete analog electronics. It benefits from the continued development of SoCs related to the IoT (Internet of Things) market. Compared with a system with a custom ASIC, this architecture based on software and SoC capabilities offers considerable advantages in terms of cost and development time. The ability to incorporate new commercial SoCs, continuously emerging from advancements in the aerospace and automotive industries, provides the system with a robust foundation for sustained growth over the years. A detailed characterization of the hardware and the system's response to different photon fluxes is presented in this article. Additionally, coupling the device with a scintillator was tested at the end of this article as a preliminary trial for future measurements, showing potential for further enhancement of the detector's capabilities.

Rapid and Sensitive Detection of Fentanyl and Its Analogs by a Novel Chemiluminescence Immunoassay

BACKGROUND

Abuse of fentanyl and its analogs is a major contributor to the opioid overdose epidemic in the United States, but detecting and quantifying trace amounts of such drugs remains a challenge without resorting to sophisticated mass spectrometry-based methods.

METHODS

A sensitive immunoassay with a sub-picogram limit of detection for fentanyl and a wide range of fentanyl analogs has been developed, using a novel high-affinity antibody fused with NanoLuc, a small-size luciferase that can emit strong and stable luminescence. When used with human urine samples, the assay has a sub-picogram limit of detection for fentanyl, with results fully concordant with LC-MS.

RESULTS

When applied to clinical samples, the novel chemiluminescence immunoassay can detect low positive fentanyl missed by routine screening immunoassays, with a limit of detection of 0.8 pg/mL in human urine. When applied to environmental samples, the assay can detect levels as low as 0.25 pg fentanyl per inch2 of environment surface. Assay turnaround time is less than 1 h, with inexpensive equipment and the potential for high-throughput automation or in-field screening.

CONCLUSIONS

We have established a novel assay that may have broad applications in clinical, environmental, occupational, and forensic scenarios for detection of trace amounts of fentanyl and its analogs.

Innovative Detection of Biomarkers Based on Chemiluminescent Nanoparticles and a Lensless Optical Sensor

The identification and quantification of biomarkers with innovative technologies is an urgent need for the precise diagnosis and follow up of human diseases. Body fluids offer a variety of informative biomarkers, which are traditionally measured with time-consuming and expensive methods. In this context, lateral flow tests (LFTs) represent a rapid and low-cost technology with a sensitivity that is potentially improvable by chemiluminescence biosensing. Here, an LFT based on gold nanoparticles functionalized with antibodies labeled with the enzyme horseradish peroxidase is combined with a lensless biosensor. This biosensor comprises four Silicon Photomultipliers (SiPM) coupled in close proximity to the LFT strip. Microfluidics for liquid handling complete the system. The development and the setup of the biosensor is carefully described and characterized. C-reactive protein was selected as a proof-of-concept biomarker to define the limit of detection, which resulted in about 0.8 pM when gold nanoparticles were used. The rapid readout (less than 5 min) and the absence of sample preparation make this biosensor promising for the direct and fast detection of human biomarkers.

A handheld luminometer with sub-attomole limit of detection for distributed applications in global health

Luminescence is ubiquitous in biology research and medicine. Conceptually simple, the detection of luminescence nonetheless faces technical challenges because relevant signals can exhibit exceptionally low radiant power densities. Although low light detection is well-established in centralized laboratory settings, the cost, size, and environmental requirements of high-performance benchtop luminometers are not compatible with geographically-distributed global health studies or resource-constrained settings. Here we present the design and application of a ~$700 US handheld, battery-powered luminometer with performance on par with high-end benchtop instruments. By pairing robust and inexpensive Silicon Photomultiplier (SiPM) sensors with a low-profile shutter system, our design compensates for sensor non-idealities and thermal drift, achieving a limit of detection of 1.6E-19 moles of firefly luciferase. Using these devices, we performed two pilot cross-sectional serology studies to assess sars-cov-2 antibody levels: a cohort in the United States, as well as a field study in Bangladesh. Results from both studies were consistent with previous work and demonstrate the device's suitability for distributed applications in global health.

User-friendly one-step disposable signal-on bioassay for glyphosate detection in water samples

The onsite detection of glyphosate requires an easy-to-handle, low-cost and disposable assay for untrained users as requested by the ASSURED guidelines. A new strategy based on the expression of fusion proteins is proposed here. A glyphosate oxidase derived from Bacillus subtilis and the 6E10 variant of the dye peroxidase from Pseudomonas putida, both fused with the carbohydrate binding module (CBM) 3a from Clostridium thermocellum, were designed and expressed, leading to GlyphOx-CBM and 6E10-CBM. Cell lysates were used to immobilise both enzymes on cotton buds' heads without any purification. The cotton buds exhibit glyphosate oxidase activity when dipped into a glyphosate-contaminated water sample containing the 6E10-CBM chromogenic substrates. The chromophore could be quantified both in the solution and on the cotton buds' heads. Photography followed by image analysis allows to detect glyphosate with a linear range of 0.25-2.5 mM and a limit of detection (LoD) of 0.12 mM. When the chromogenic substrates are replaced by luminol, the chemiluminescence reaction allows the detection of glyphosate with a linear range of 2-500 μM and a LoD of 0.45 μM. No interference was observed using glyphosate analogues (glycine, sarcosine, aminomethylphosphonic acid) or other herbicides used in a mixture. Only cysteine was found to inhibit 6E10-CBM. Two river waters spiked with glyphosate lead to recoveries of 64-131%. This work describes a very easy-to-handle and inexpensive signal-on bioassay for glyphosate detection in real surface water samples.

New synthetic red- and orange-emitting luciferases to upgrade in vitro and 3D cell biosensing

Bioluminescence (BL), i.e., the emission of light in living organisms, has become an indispensable tool for a plethora of applications including bioassays, biosensors, and in vivo imaging. Current efforts are focused on the obtainment of new luciferases having optimized properties, such as improved thermostability at 37 °C, pH-insensitive emission, high quantum yield, extended kinetics and red-shifted emission. To address these issues we have obtained two new synthetic luciferases, an orange and a red-emitting luciferase, which were designed to achieve high sensitivity (BoLuc) and multiplexing capability (BrLuc) for in vitro and in vivo biosensing using as a starting template a recently developed thermostable synthetic luciferase (BgLuc). Both luciferases were characterized in terms of emission behaviour and thermal and pH stability showing promising features as reporter proteins and BL probes. As proof-of-principle application, an inflammation assay based on Human Embryonic Kidney (HEK293T) 3D cell cultures was developed using either the orange or the red-emitting mutant. The assay provided good analytical performance, with limits of detection for Tumor Necrosis Factor (TNFα) of 0.06 and 0.12 ng mL-1 for BoLuc and BrLuc, respectively. Moreover, since these luciferases require the same substrate, D-luciferin, they can be easily implemented in dual-color assays with a significant reduction of total cost per assay.

Highly Sensitive, Portable Detection System for Multiplex Chemiluminescence Analysis

Chemiluminescence (CL) has emerged as a critical tool for the sensing and quantification of various bioanalytes in virtually all clinical fields. However, the rapid nature of many CL reactions raises challenges for typical low-cost optical sensors such as cameras to achieve accurate and sensitive detection. Meanwhile, classic sensors such as photomultiplier tubes are highly sensitive but lack spatial multiplexing capabilities and are generally not suited for point-of-care applications outside a standard laboratory setting. To address this issue, in this paper, a miniaturized and versatile silicon-photomultiplier-based fiber-integrated CL device (SFCD) was designed for sensitive multiplex CL detection. The SFCD comprises a silicon photomultiplier array coupled to an array of high numerical aperture plastic optical fibers to achieve 16-plex detection. The optical fibers ensure efficient light collection while allowing the fixed detector to be mated with diverse sample geometries (e.g., circular or grid), simply by adjusting the fiber configuration. In a head-to-head comparison with a lens-based camera system featuring a cooled detector, the SFCD achieved a 14-fold improved limit of detection in both direct and enzyme-mediated CL reactions. The SFCD also features improved compactness and lower cost, as well as faster temporal resolution compared with camera-based systems while preserving spatial multiplexing and good environmental robustness. Thus, the SFCD has excellent potential for point-of-care biosensing applications.

Application of biosensors in cancers, an overview

The deadliest disease in the world, cancer, kills many people every year. The early detection is the only hope for the survival of malignant cancer patients. As a result, in the preliminary stages of, the diagnosis of cancer biomarkers at the cellular level is critical for improving cancer patient survival rates. For decades, scientists have focused their efforts on the invention of biosensors. Biosensors, in addition to being employed in other practical scenarios, can essentially function as cost effective and highly efficient devices for this purpose. Traditional cancer screening procedures are expensive, time-consuming, and inconvenient for repeat screenings. Biomarker-based cancer diagnosis, on the other hand, is rising as one of the most potential tools for early detection, disease progression monitoring, and eventual cancer treatment. As Biosensor is an analytical device, it allows the selected analyte to bind to the biomolecules being studied (for example RNA, DNA, tissue, proteins, and cells). They can be divided based on the kind of biorecognition or transducer elements on the sensor. Most biosensor analyses necessitate the analyte being labeled with a specific marker. In this review article, the application of distinct variants of biosensors against cancer has been described.

Super-Stable Metal-Organic Framework (MOF)/Luciferase Paper-Sensing Platform for Rapid ATP Detection

Adenosine triphosphate (ATP) determination has been used for many decades to assess microbial contamination for hygiene monitoring in different locations and workplace environments. Highly sophisticated methods have been reported, yet commercially available kits rely on a luciferase-luciferin system and require storage and shipping at controlled temperatures (+4 or -20 °C). The applicability of these systems is limited by the need for a secure cold chain, which is not always applicable, especially in remote areas or low-resource settings. In this scenario, easy-to-handle and portable sensors would be highly valuable. Prompted by this need, we developed a bioluminescence paper biosensor for ATP monitoring in which a new luciferase mutant was combined with a metal-organic framework (MOF); i.e., zeolitic imidazolate framework-8 (ZIF-8). A paper biosensor was developed, ZIF-8@Luc paper sensor, and interfaced with different portable light detectors, including a silicon photomultiplier (SiPM) and smartphones. The use of ZIF-8 not only provided a five-fold increase in the bioluminescence signal, but also significantly improved the stability of the sensor, both at +4 and +28 °C. The ATP content in complex biological matrices was analyzed with the ZIF-8@Luc paper sensor, enabling detection down to 7 × 10^-12 moles of ATP and 8 × 10^-13 moles in bacterial lysates and urine samples, respectively. The ZIF-8@Luc sensor could, therefore, be applied in many fields in which ATP monitoring is required such as the control of microbial contamination.

A SiPM-Enabled Portable Delayed Fluorescence Photon Counting Device: Climatic Plant Stress Biosensing

A portable and sensitive time-resolved biosensor for capturing very low intensity light emission is a promising avenue to study plant delayed fluorescence. These weak emissions provide insight on plant health and can be useful in plant science as well as in the development of accurate feedback indicators for plant growth and yield in applications of agricultural crop cultivation. A field-based delayed fluorescence device is also desirable to enable monitoring of plant stress response to climate change. Among basic techniques for the detection of rapidly fluctuating low intensity light is photon counting. Despite its vast utility, photon counting techniques often relying on photomultiplier tube (PMT) technology, having restricted use in agricultural and environment measurements of plant stress outside of the laboratory setting, mainly due to the prohibitive cost of the equipment, high voltage nature, and the complexity of its operation. However, recent development of the new generation solid-state silicon photomultiplier (SiPM) single photon avalanche diode array has enabled the availability of high quantum efficiency, easy-to-operate, compact, photon counting systems which are not constrained to sophisticated laboratories, and are accessible owing to their low-cost. In this contribution, we have conceived, fabricated and validated a novel SiPM-based photon counting device with integrated plug-and-play excitation LED, all housed inside a miniaturized sample chamber to record weak delayed fluorescence lifetime response from plant leaves subjected to varying temperature condition and drought stress. Findings from our device show that delayed fluorescence reports on the inactivation to the plant's photosystem II function in response to unfavorable acute environmental heat and cold shock stress as well as chronic water deprivation. Results from our proof-of-concept miniaturized prototype demonstrate a new, simple and effective photon counting instrument is achieved, one which can be deployed in-field to rapidly and minimally invasively assess plant physiological growth and health based on rapid, ultra-weak delayed fluorescence measurements directly from a plant leaf.

Comparative Analysis of NanoLuc Luciferase and Alkaline Phosphatase Luminescence Reporter Systems for Phage-Based Detection of Bacteria

Reporter phage assays are a promising alternative to culture-based assays for rapidly detecting viable bacteria. The reporter systems used in phage-based detection are typically enzymes and their corresponding substrates that provide a signal following infection and expression. While several reporter systems have been developed, comparing reporter systems based on reported bacteria detection limits from literature can be challenging due to factors other than the reporter system that influence detection capabilities. To advance the development of phage-based assays, a systematic comparison and understanding of the components are necessary. The objective of this study was to directly compare two common enzyme-mediated luminescence reporter systems, NanoLuc/Nano-Glo and alkaline phosphatase (ALP*)/DynaLight, for phage-based detection of bacteria. The detection limits of the purified enzymes were determined, as well as the expression levels and bacteria detection capabilities following engineering of the coding genes into T7 phage and infection of E. coli BL21. When comparing the sensitivity of the purified enzymes, NLuc/Nano-Glo enzyme/substrate system demonstrated a lower detection limit than ALP*/DynaLight. In addition, the expression of the NLuc reporter following phage infection of E. coli was greater than ALP*. The lower detection limit combined with the higher expression resulted in a greater than 100-fold increase in sensitivity for the NLuc/Nano-Glo^® reporter system compared to ALP*/DynaLight when used for the detection of E. coli in a model system. These findings provide a comparative analysis of two common reporter systems used for phage-based detection of bacteria and a foundational understanding of these systems for engineering future reporter phage assays.

A Luciferase Mutant with Improved Brightness and Stability for Whole-Cell Bioluminescent Biosensors and In Vitro Biosensing

The availability of new bioluminescent proteins with tuned properties, both in terms of emission wavelength, kinetics and protein stability, is highly valuable in the bioanalytical field, with the potential to improve the sensitivity and analytical performance of the currently used methods for ATP detection, whole-cell biosensors, and viability assays among others. We present a new luciferase mutant, called BgLuc, suitable for developing whole-cell biosensors and in vitro biosensors characterized by a bioluminescence maximum of 548 nm, narrow emission bandwidth, favorable kinetic properties, and excellent pH- and thermo-stabilities at 37 and 45 °C and pH from 5.0 to 8.0. We assessed the suitability of this new luciferase for whole-cell biosensing with a cell-based bioreporter assay for Nuclear Factor-kappa B (NF-kB) signal transduction pathway using 2D and 3D human embryonic kidney (HEK293T) cells, and for ATP detection with the purified enzyme. In both cases the luciferase showed suitable for sensitive detection of the target analytes, with better or similar performance than the commercial counterparts.

A microfluidic device and instrument prototypes for the detection of Escherichia coli in water samples using a phage-based bioluminescence assay

Current quantification methods of Escherichia coli (E. coli) contamination in water samples involve long incubation, laboratory equipment and facilities, or complex processes that require specialized training for accurate operation and interpretation. To address these limitations, we have developed a microfluidic device and portable instrument prototypes capable of performing a rapid and highly sensitive bacteriophage-based assay to detect E. coli cells with detection limit comparable to traditional methods in a fraction of the time. The microfluidic device combines membrane filtration and selective enrichment using T7-NanoLuc-CBM, a genetically engineered bacteriophage, to identify 4.1 E. coli CFU in 100 mL of drinking water within 5.5 hours. The microfluidic device was designed and tested to process up to 100 mL of real-world drinking water samples with turbidities below 10 NTU. Prototypes of custom instrumentation, compatible with our valveless microfluidic device and capable of performing all of the assay's units of operation with minimal user intervention, demonstrated similar assay performance to that obtained on the benchtop assay. This research is the first step towards a faster, portable, and semi-automated, phage-based microfluidic platform for improved in-field water quality monitoring in low-resource settings.

High sensitivity and wide range chlorophyll-a determination by simultaneous measurement of absorbance and fluorescence using a linear CCD

In the determination of chlorophyll with the fluorescence method in the natural water, the suspended particles and colloids will seriously interfere with the incident light and the fluorescence. Based on the analysis of the interaction between light and the measured substances, a high sensitivity, wide range of chlorophyll-a concentration measurement strategy, which combines optical information of fluorescence and absorbance with the CCD integration time transformation method, is proposed. Correspondingly, a novel algorithm, which can significantly correct the attenuation of incident light due to the absorption of suspended particles and the deviation of detected fluorescence caused by the scattered light and reflected light, is proposed to realize turbidity compensation. For verification, a self-designed compact optical experimental device consisting of a single LED and a linear CCD was set up to obtain the fluorescence spectrum and absorbance spectrum simultaneously. The experimental results demonstrate that the compensation strategy can commendably compensate for the impact of the suspended particles. The relative error of chlorophyll-a measurement is less than 5%, even in a high turbidity environment. Furthermore, the minimum detection limit is significantly reduced from conventional 0.01 μg/L to 0.0025 μg/L in the range of 0.0025-130 μg/L with the CCD integration time transformation method, which improves the measurement sensitivity. This device and method have the potential to be applied to the in situ online measurement of chlorophyll-a concentration in natural water.

ATP Sensing Paper with Smartphone Bioluminescence-Based Detection

Adenosine-5'-triphosphate (ATP) is the primary energy carrier in all living organisms, and its detection in living cells represents a well-established approach. ATP-driven bioluminescence (BL) relying on the D-luciferin-luciferase reaction is a bioanalytical tool widely employed for monitoring hygiene and microbial contamination of foods.Here, we report a straightforward method for ATP BL detection using an ATP sensing paper fabricated with an alternative freeze-dry procedure. The assay can be easily implemented in laboratories equipped with (i) freeze-drying, wax printing, and 3D printing technologies and (ii) instrumentation for BL detection such as benchtop luminometers and portable light detectors including a smartphone camera without the need for additional equipment.

Orthogonal paper biosensor for mercury(II) combining bioluminescence and colorimetric smartphone detection

Mercury contamination in the environment has reached alarming levels. Due to its persistence and bioaccumulation, mercury is one of the most widespread toxic heavy metals found in air, water and food. Thus, it is mandatory to monitor mercury and its compounds, and the availability of sensitive and rapid biosensors is highly valuable. We developed a low-cost biosensor for orthogonal detection of mercury(II) integrating three different biorecognition principles on a three-leaf paper: i) a mercury-specific bioluminescent Escherichia coli bioreporter strain expressing NanoLuc luciferase as reporter protein, ii) a purified β-galactosidase (β-gal) enzyme which is irreversibly inhibited by mercury and other metal ions, and iii) an Aliivibrio fischeri bioluminescent strain which is used to quantitatively assess sample toxicity and correct the analytical signal accordingly. Both sensory elements and substrates, Furimazine for the bioluminescent reporter strain and chlorophenol red-β-D-galactopyranoside for colorimetric detection of β-gal, were integrated in the paper sensor to provide a stable all-in-one disposable cartridge which can be easily snapped into a smartphone with a clover-shaped 3D printed housing. This is the first integration of bioluminescence and colorimetric detection on a smartphone-paper sensor, providing a readout within 15 and 60 min for the colorimetric and bioluminescent detection respectively. The biosensor was applied to water samples spiked with different concentrations of mercury, interferents and toxic chemicals providing a limit of detection for Hg(II) at the ppb levels.

Paper-Based Immunosensors with Bio-Chemiluminescence Detection

Since the introduction of paper-based analytical devices as potential diagnostic platforms a few decades ago, huge efforts have been made in this field to develop systems suitable for meeting the requirements for the point-of-care (POC) approach. Considerable progress has been achieved in the adaptation of existing analysis methods to a paper-based format, especially considering the chemiluminescent (CL)-immunoassays-based techniques. The implementation of biospecific assays with CL detection and paper-based technology represents an ideal solution for the development of portable analytical devices for on-site applications, since the peculiarities of these features create a unique combination for fitting the POC purposes. Despite this, the scientific production is not paralleled by the diffusion of such devices into everyday life. This review aims to highlight the open issues that are responsible for this discrepancy and to find the aspects that require a focused and targeted research to make these methods really applicable in routine analysis.