Dual channel detection of ultra low concentration of bacteria in real time by scanning FCS

Digital Protein Detection in Bulk Solutions

Quick and accurate molecular diagnostics in protein detection can greatly benefit medicine in disease diagnosis and lead to positive patient outcomes. However, specialized equipment used in clinical laboratories often comes with trade-offs between operation and function serving a single role for very specific needs. For example, to achieve high analytical sensitivity and specificity, instruments such as high-performance liquid chromatography and/or liquid chromatography-mass spectrometry use a complex instrument design and require thorough training of the users. On the other hand, simple tests such as protein detection in urinary tract infection using dip-stick assays provide very quick results but suffer from poor analytical sensitivity. Here, we present an application study for the 3D particle counter technology, which is based on optical confocal detection in order to scan large sample volumes (0.5-3 mL) in glass cuvettes, that aims to close the gap between analytical sensitivity and turnover assay time and simplify protein detection by adopting bead-based immunoassays. Combining the 3D particle counter technology with bead-based immunoassays, a subpicomolar limit of detection-ranging from 119 to 346 fM-was achieved within 3.5-hour assay time for recombinant mouse interleukin 6 detection. As an alternative instrument to a flow cytometer, the 3D particle counter takes advantages of bead-based immunoassays and provides unique accessibility and flexibility for users.

Bacterial Infection Diagnosis and Antibiotic Prescription in 3 h as an Answer to Antibiotic Resistance: The Case of Urinary Tract Infections

Current methods for the diagnosis of urinary tract infections with antimicrobial susceptibility testing take 2–3 days and require a clinical laboratory. The lack of a rapid, point-of-care antibiotic susceptibility test (AST) has contributed to the misuse of antibiotics when treating urinary tract infections (UTIs) and consequently to the rise of multi-drug-resistant organisms. The current clinical approach has led to reduced treatment options and increased costs of diagnosis and therapy. To address this issue, novel diagnostics are needed for the timely determination of antimicrobial susceptibility. We present a rapid, point-of-care, phenotypic AST device that can report the antibiotic susceptibility/resistance of a uropathogen to a panel of antibiotics in as few as 3 h by utilizing fluorescent-labelling chemistry and a highly sensitive particle-counting instrument. We analysed 744 urine samples from the outpatients and inpatients of two Italian hospitals. The 130 UTI-positive patient urine samples we found were measured using a panel of six common UTI antibiotics plus a growth control. By comparing our results to hospital laboratory urine cultures, we obtained an overall sensitivity = 81%, a specificity = 83%, an SPV (sensitivity predicted value) = 95%, and an RPV (resistance predicted value) = 54%. According to our preliminary data, the sensitivity predicted value for a single antibiotic agent was 95%, thus allowing (in the vast majority of cases) an early (within 3 h) recognition of an effective agent for a single patient.

Scanning single-molecule counting system for Eprobe with highly simple and effective approach

Here, we report a rapid and ultra-sensitive detection technique for fluorescent molecules called scanning single molecular counting (SSMC). The method uses a fluorescence-based digital measurement system to count single molecules in a solution. In this technique, noise is reduced by conforming the signal shape to the intensity distribution of the excitation light via a circular scan of the confocal region. This simple technique allows the fluorescent molecules to freely diffuse into the solution through the confocal region and be counted one by one and does not require statistical analysis. Using this technique, 28 to 62 aM fluorescent dye was detected through measurement for 600 s. Furthermore, we achieved a good signal-to-noise ratio (S/N = 2326) under the condition of 100 pM target nucleic acid by only mixing a hybridization-sensitive fluorescent probe, called Eprobe, into the target oligonucleotide solution. Combination of SSMC and Eprobe provides a simple, rapid, amplification-free, and high-sensitive target nucleic acid detection system. This method is promising for future applications to detect particularly difficult to design primers for amplification as miRNAs and other short oligo nucleotide biomarkers by only hybridization with high sensitivity.

Rapid Detection of β-Lactamase-Producing Bacteria Using the Integrated Comprehensive Droplet Digital Detection (IC 3D) System

Antibiotic-resistant bacteria have emerged as an imminent global threat. The lack of rapid and sensitive diagnostic techniques leaves health care providers with inadequate resources for guiding therapy and risks the lives of patients. The traditional plate culturing methods for identifying antibiotic-resistant bacteria is laborious and time-consuming. Bulk PCR (Polymerase Chain Reaction) and qPCR are limited by poor detection sensitivity, which is critical for the early-stage detection of bloodstream infections. In this study, we introduce a technique for detecting β-lactamase-producing bacteria at single-cell sensitivity based on a commercial β-lactamase sensor (Fluorocillin), droplet microfluidics, and a custom 3D particle counter. Bacteria-containing samples were encapsulated within picoliter-sized droplets at the single-cell level and cultured within water-in-oil droplets containing antibiotics and the Fluorocillin sensor. Then, fluorescent droplets were digitally quantified with the 3D particle counter, which is capable of analyzing milliliter-scale volumes of collected droplets within 10 min. The fluorescence signal from single-colony droplets was detectable in less than 5 h, and the 3D scanning was performed in less than 10 min, which was significantly faster than conventional culture-based methods. In this approach, the limit of detection achieved was about 10 bacterial cells per mL of sample, and the turnaround time from sample to result was less than 6 h. This study demonstrates a promising strategy for the detection of β-lactamase-producing bacteria using the recently developed IC 3D system.

Rapid isolation of rare targets from large fluid volumes

Rapidly isolating rare targets from larger, clinically relevant fluid volumes remains an unresolved problem in biomedicine and diagnosis. Here, we describe how 3D particle sorting can enrich targets at ultralow concentrations over 100-fold within minutes not possible with conventional approaches. Current clinical devices based on biochemical extraction and microfluidic solutions typically require high concentrations and/or can only process sub-milliliter volumes in time. In a proof-of-concept application, we isolated bacteria from whole blood as demanded for rapid sepsis diagnosis where minimal numbers of bacteria need to be found in a 1–10 mL blood sample. After sample encapsulation in droplets and target enrichment with the 3D particle sorter within a few minutes, downstream analyses were able to identify bacteria and test for antibiotic susceptibility, information which is critical for successful treatment of bloodstream infections.

Microfluidic systems for rapid antibiotic susceptibility tests (ASTs) at the single-cell level

Infectious diseases caused by multidrug resistant (MDR) bacterial pathogens are impending threats to global health. Since delays in identifying drug resistance would significantly increase mortality, fast and accurate antibiotic susceptibility tests (ASTs) are critical for addressing the antibiotic resistance issue. However, the conventional methods for ASTs are always labor-intensive, imprecise, complex and slow (taking 2-3 days). To address these issues, some advanced microfluidic systems have been designed for rapid phenotypic and genotypic analysis of antibiotic resistance. This review highlights the recent development of microfluidics-based ASTs at the single-cell or single-molecule level for guiding antibiotic treatment decisions and predicting therapeutic outcomes.

A rapid, point-of-care antibiotic susceptibility test for urinary tract infections

Introduction. The alarming rise in urinary tract infection (UTI) antimicrobial resistance has resulted from a combination of high prevalence, low specificity and the lack of a rapid, point-of-care (POC) antibiotic susceptibility test (AST), which has led to the overuse/inappropriate use of antibiotics.Aim. This study aimed to evaluate the performance of a rapid POC phenotypic AST device in reporting susceptibility information within 2 h.Methodology. Instrument calibration was performed with model bacteria and fluorescent microbeads to determine the dynamic range and limit of detection for quantifying concentrations of bacteria and demonstrate the ability to rapidly differentiate susceptible and resistant model bacteria. We then evaluated 30 presumptive UTI-positive patient urine samples in a clinical pilot study using a panel of 5 common UTI antibiotics plus a growth control and compared our results to the hospital standard of care AST.Results. Our device was able to robustly detect and quantify bacteria concentrations from 50 to 105 colony-forming units (c.f.u.) ml-1. The high sensitivity of this measurement technique enabled the device to differentiate between susceptible and resistant model bacteria with 100 % specificity over a 2 h growth period. In the clinical pilot study, an overall categorical agreement (CA) of 90.7 % was observed (sensitivity=91.4 %, specificity=88.9 %, n=97) with performance for individual drugs ranging from 85 % CA (ceftazidime) to 100 % (nitrofurantoin).Conclusions. By reducing the typical timeframe for susceptibility testing from 2-3 days to 2 h, our POC phenotypic AST can provide critical information to clinicians prior to the administration of antibiotic therapy.

A Fluorescence Correlation Spectrometer for Measurements in Cuvettes

We have developed a fluorescence correlation spectroscopy (FCS) setup for performing single-molecule measurements on samples inside regular cuvettes. The cuvette FCS uses a horizontally mounted extra-long working distance, 0.7 NA, air objective with a working distance of >1.8 mm instead of a high NA water or oil immersion objective. The performance of the cuvette FCS is found to be highly sensitive to the quality and alignment of the cuvette. The radial resolution and effective observation volume obtained using the optimized setup are ∼340 nm and 1.8 fL, respectively. The highest molecular brightness and the signal/noise ratio in the autocorrelation data achieved using an aqueous solution of rhodamine B are greater than 44 kHz and 110, respectively. Here, we demonstrate two major advantages of cuvette FCS. For example, the cuvette FCS can be used for measurements over a wide range of temperatures that is beyond the range permitted in the microscope-based FCS. Furthermore, cuvette FCS can be coupled to automatic titrators to study urea-dependent unfolding of proteins with unprecedented accuracy. The ease of use and compatibility with various accessories will enable applications of cuvette FCS in the experiments that are regularly performed in spectrofluorometers but are generally avoided in microscope-based FCS.

Fluorescence lifetime detection with particle counting devices

Fluorescence-based single particle counting devices have become very powerful tools for human health-related applications such as the detection of blood-borne pathogens. Instead of passing the sample fluid through a thin tube or microfluidic chip, as it is commonly practiced in flow cytometers and sorter devices, single particle counters scan the fluid volume by rotation and translation of the sample container. Hence, single particle counters are not limited by the fluid flow friction and can scan a large volume in a short timeframe while maintaining high sensitivity. A single particle can be detected in a milliliter of the fluid sample within minutes, and diagnostics are being developed using this principle. Until now, signal detection with particle counters has been based on signal intensity and signal separation into multiple wavelength bands coupled with multiple detectors, which limits the number of species that can be resolved. In this paper, we applied fluorescence lifetime detection to single particle counting to increase specificity and enable multiplexing with a single detector. We demonstrate how this principle can be used for diagnostic assays based on fluorescence quenching.

Building, Characterization, and Applications of Cuvette-FCS in Denaturant-Induced Expansion of Globular and Disordered Proteins

Fluorescence correlation spectroscopy (FCS) is a single-molecule sensitive technique with widespread applications in biophysics. However, conventional microscope-based FCS setups have limitations in performing certain experiments such as those requiring agitations such as stirring or heating, and those involving measurements in solvents with the mismatch of refractive indices. We have recently developed an FCS setup that is suitable for performing measurements inside regular cuvettes. The cuvette-FCS is suitable for performing single-molecule measurements in experiments that are regularly performed in spectrofluorometers but are generally avoided in microscope-based FCS. Here we describe building and characterization of the performance of the cuvette-FCS setup in detail. Finally, we have used a natively folded protein and an intrinsically disordered protein to demonstrate and describe how cuvette-FCS can be applied conveniently to measure urea-dependent expansion of hydrodynamic size of proteins.

Emerging Technologies for Molecular Diagnosis of Sepsis

Rapid and accurate profiling of infection-causing pathogens remains a significant challenge in modern health care. Despite advances in molecular diagnostic techniques, blood culture analysis remains the gold standard for diagnosing sepsis. However, this method is too slow and cumbersome to significantly influence the initial management of patients. The swift initiation of precise and targeted antibiotic therapies depends on the ability of a sepsis diagnostic test to capture clinically relevant organisms along with antimicrobial resistance within 1 to 3 h. The administration of appropriate, narrow-spectrum antibiotics demands that such a test be extremely sensitive with a high negative predictive value. In addition, it should utilize small sample volumes and detect polymicrobial infections and contaminants. All of this must be accomplished with a platform that is easily integrated into the clinical workflow. In this review, we outline the limitations of routine blood culture testing and discuss how emerging sepsis technologies are converging on the characteristics of the ideal sepsis diagnostic test. We include seven molecular technologies that have been validated on clinical blood specimens or mock samples using human blood. In addition, we discuss advances in machine learning technologies that use electronic medical record data to provide contextual evaluation support for clinical decision-making.

Digital Assays Part II: Digital Protein and Cell Assays

A digital assay is one in which the sample is partitioned into many containers such that each partition contains a discrete number of biological entities (0, 1, 2, 3, . . .). A powerful technique in the biologist’s toolkit, digital assays bring a new level of precision in quantifying nucleic acids, measuring proteins and their enzymatic activity, and probing single-cell genotype and phenotype. Where part I of this review focused on the fundamentals of partitioning and digital PCR, part II turns its attention to digital protein and cell assays. Digital enzyme assays measure the kinetics of single proteins with enzymatic activity. Digital enzyme-linked immunoassays (ELISAs) quantify antigenic proteins with 2 to 3 log lower detection limit than conventional ELISA, making them well suited for low-abundance biomarkers. Digital cell assays probe single-cell genotype and phenotype, including gene expression, intracellular and surface proteins, metabolic activity, cytotoxicity, and transcriptomes (scRNA-seq). These methods exploit partitioning to 1) isolate single cells or proteins, 2) detect their activity via enzymatic amplification, and 3) tag them individually by coencapsulating them with molecular barcodes. When scaled, digital assays reveal stochastic differences between proteins or cells within a population, a key to understanding biological heterogeneity. This review is intended to give a broad perspective to scientists interested in adopting digital assays into their workflows.

Digital quantification of miRNA directly in plasma using integrated comprehensive droplet digital detection

Quantification of miRNAs in blood can be potentially used for early disease detection, surveillance monitoring and drug response evaluation. However, quantitative and robust measurement of miRNAs in blood is still a major challenge in large part due to their low concentration and complicated sample preparation processes typically required in conventional assays. Here, we present the 'Integrated Comprehensive Droplet Digital Detection' (IC 3D) system where the plasma sample containing target miRNAs is encapsulated into microdroplets, enzymatically amplified and digitally counted using a novel, high-throughput 3D particle counter. Using Let-7a as a target, we demonstrate that IC 3D can specifically quantify target miRNA directly from blood plasma at extremely low concentrations ranging from 10s to 10 000 copies per mL in ≤3 hours without the need for sample processing such as RNA extraction. Using this new tool, we demonstrate that target miRNA content in colon cancer patient blood is significantly higher than that in healthy donor samples. Our IC 3D system has the potential to introduce a new paradigm for rapid, sensitive and specific detection of low-abundance biomarkers in biological samples with minimal sample processing.

Rapid detection of single bacteria in unprocessed blood using Integrated Comprehensive Droplet Digital Detection

Blood stream infection or sepsis is a major health problem worldwide, with extremely high mortality, which is partly due to the inability to rapidly detect and identify bacteria in the early stages of infection. Here we present a new technology termed 'Integrated Comprehensive Droplet Digital Detection' (IC 3D) that can selectively detect bacteria directly from milliliters of diluted blood at single-cell sensitivity in a one-step, culture- and amplification-free process within 1.5-4 h. The IC 3D integrates real-time, DNAzyme-based sensors, droplet microencapsulation and a high-throughput 3D particle counter system. Using Escherichia coli as a target, we demonstrate that the IC 3D can provide absolute quantification of both stock and clinical isolates of E. coli in spiked blood within a broad range of extremely low concentration from 1 to 10,000 bacteria per ml with exceptional robustness and limit of detection in the single digit regime.

Simplified confocal microscope for counting particles at low concentrations

We describe a compact scanning confocal fluorescence microscope capable of detecting particles concentrations less than 100 particles∕ml in ~15 min. The system mechanically moves a cuvette containing ~3 ml of sample. A relatively large confocal volume is observed within the cuvette using a 1 mm pinhole in front of a detection PMT. Due to the motion of the sample, particles traverse the confocal volume quickly, and analysis by pattern recognition qualifies spikes in the emission intensity data and counts them as events. We show linearity of detection as a function of concentration and also characterize statistical behavior of the instrument. We calculate a detection sensitivity of the system using 3 μm fluorescent microspheres to be 5 particles/ml. Furthermore, to demonstrate biological application, we performed a dilution series to quantify stained E. coli and yeast cells. We counted E. coli cells at a concentration as low as 30 cells∕ml in 10 min/sample.