Upconversion nanoparticle-based Förster resonance energy transfer for detecting the IS6110 sequence of Mycobacterium tuberculosis complex in sputum

Integrating Paper-Based Microfluidics and Lateral Flow Strip into Nucleic Acid Amplification Device toward Rapid, Low-Cost, and Visual Diagnosis of Multiple Mycobacteria

Efficient diagnosis of mycobacterial infections can effectively manage and prevent the transmission of infectious diseases. Unfortunately, existing diagnostic strategies are challenged by long assay times, high costs, and highly specialized expertise to distinguish between pulmonary tuberculosis (PTB) and nontuberculous mycobacterial pulmonary diseases (NTM-PDs). Herein, in this study, an optimized 3D paper-based analytical device (µPAD) is incorporated with a closed lateral flow (LF) strip into a loop-mediated isothermal amplification (LAMP) device (3D-µPAD-LF-LAMP) for rapid, low-cost, and visual detection of pathogenic mycobacteria. The platform's microfluidic feature enhanced the nucleic acid amplification, thereby reducing the costs and time as compared to boiling, easyMAG, and QIAGEN techniques. Moreover, the LF unit is specifically designed to minimize aerosol contamination for a user-friendly and visual readout. 3D-µPAD-LF-LAMP is optimized and assessed using standard strains, demonstrating a limit of detection (LOD) down to 10 fg reaction-1 . In a cohort of 815 patients, 3D-µPAD-LF-LAMP displays significantly better sensitivity, specificity, negative predictive value (NPV), positive predictive value (PPV), and diagnostic accuracy than conventional bacterial culture and Xpert techniques. Collectively, 3D-µPAD-LF-LAMP demonstrates enhanced accessibility, efficiency, and practicality for the diagnosis of multiple pathogenic mycobacteria, which can be applied across diverse clinical settings, thereby ultimately improving public health outcomes.

Advances in the detection and diagnosis of tuberculosis using optical-based devices

Tuberculosis (TB), a bacterial infection caused by Mycobacterium tuberculosis, is highly contagious and can lead to severe health complications if left untreated. This review article discusses the importance of early detection and treatment and its global incidence and epidemiology, emphasizing its impact on vulnerable populations and its role as a major cause of death worldwide. Furthermore, it highlights the challenges faced with diagnosing TB. To overcome these challenges, point-of-care devices have emerged as promising tools for rapid and accurate TB detection. These include devices such as nucleic acid amplification tests (NAATs), lateral flow assays (LFAs), and microfluidic-based assays, which offer advantages such as rapid results, portability, and the ability to detect drug-resistant strains. Optical-based devices, such as photonic micro-ring sensors, silicon platform-based sensors, plasmonic-based platforms, microfluidics, and smartphone imaging, are some of the highlighted optical-based devices with the potential to detect TB. These devices can detect TB in sputum samples with high sensitivity and specificity. Optical-based diagnostic devices have the potential to offer the advantages of detecting low concentrations of target molecules and being adaptable to detect multiple targets simultaneously. Using these devices in a clinical setting makes them suitable for their application in improving access to diagnostic testing that enables earlier detection and treatment of TB. Furthermore, these devices would improve TB's global health issue, which requires comprehensive research, prevention, and treatment efforts.

An insight to the recent advancements in detection of Mycobacterium tuberculosis using biosensors: A systematic review

Since ancient times, Tuberculosis (TB) has been a severe invasive illness that has been prevalent for thousands of years and is also known as "consumption" or phthisis. TB is the most common chronic lung bacterial illness in the world, killing over 2 million people each year, caused by Mycobacterium tuberculosis (MTB). As per the reports of WHO, in spite of technology advancements, the average rate of decline in global TB infections from 2000-2018 was only 1.6% per year, and the worldwide reduction in TB deaths was only 11%. In addition, COVID-19 pandemic has reversed years of global progress in tackling TB with fewer diagnosed cases. The majority of undiagnosed patients of TB are found in low- and middle-income countries where the GeneXpert MTB/RIF assay and sputum smear microscopy have been approved by the WHO as reference procedures for quickly detecting TB. Biosensors, like other cutting-edge technologies, have piqued researchers' interest since they offer a quick and accurate way to identify MTB. Modern integrated technologies allow for the rapid, low-cost, and highly precise detection of analytes in extremely little amounts of sample by biosensors. Here in this review, we outlined the severity of tuberculosis (TB) and the most recent developments in the biosensors sector, as well as their various kinds and benefits for TB detection. The review also emphasizes how widespread TB is and how it needs accurate diagnosis and effective treatment.

Development of a Dual Mode UCNPs-MB Biosensor in Combination with PCR for Sensitive Detection of Salmonella

In recent years, the high prevalence of Salmonella has emerged as a serious threat to public safety, prompting attempts to utilize accurate, rapid, and direct methods to ensure food safety. In this study, a multifunctional platform featuring dual-mode detection channels (colorimetric-fluorescence) combined with polymer chain reaction (PCR) was proposed for the sensitive and rapid detection of Salmonella. Additionally, the colorimetric measurements were achieved by color changes induced by methylene blue (MB) insertion into the double-stranded DNA, and the fluorescence measurements were performed by internal filter effect (IFE)-induced fluorescence quenching of upconversion nanoparticles (UCNPs) by MB. The results showed that the IFE and PCR amplification processes improved the sensitivity of the sensor towards Salmonella detection, with a limit of detection (LOD) of 21.8 CFU/mL. Moreover, this colorimetric-fluorescence dual-mode PCR biosensor was applied to determine Salmonella in food samples, such as chicken, egg, and fish, which produced satisfactory results. Overall, the present study results demonstrate the potential for combining PCR amplification with IFE to develop an efficient and reliable dual-mode analysis platform to safeguard food security.

A novel ADA-coated UCNPs@NB sensing platform combined with nucleic acid amplification for rapid detection of Escherichia coli

In this study, we reported a novel sensing platform based on fluorescence quenching composed of alendronic acid (ADA) coated upconversion nanoparticles (UCNPs) and Nile Blue (NB) combined with polymerase chain reaction (PCR) for rapid, sensitive, and specific detection of Escherichia coli (E. coli). As a fluorescence acceptor, NB has a broad absorption band and can quench upconversion fluorescence intensity at 544 nm and 658 nm based on IFE. PCR is a double-stranded DNA (dsDNA) amplification technique with high specificity. The NB-dsDNA complex can be formed by intercalation of NB between base pairs and groove of dsDNA, leading to upconversion fluorescence recovery. The ADA-coated UCNPs@NB sensing platform achieved to detect E. coli in 1.5 h, with a lower limit of detection (33 CFU mL^-1). In addition, the sensitivity of the ADA@UCNPs-NB fluorescence sensor under different PCR cycle numbers was discussed. The results showed that the proposed sensor could effectively shorten the assay time (1.0 h) while maintaining excellent sensitivity. This study demonstrated a rapid and sensitive analytical method for detecting E. coli in chicken, providing a reference for constructing PCR fluorescence sensors.

Engineered upconversion nanocarriers for synergistic breast cancer imaging and therapy: Current state of art

Breast cancer is the most common type of cancer in women and is the second leading cause of cancer-related deaths worldwide. Early diagnosis and effective therapeutic interventions are critical determinants that can improve survival and quality of life in breast cancer patients. Nanotheranostics are emerging interventions that offer the dual benefit of in vivo diagnosis and therapeutics through a single nano-sized carrier. Rare earth metal-doped upconversion nanoparticles (UCNPs) with their ability to convert near-infrared light to visible light or UV light in vivo settings have gained special attraction due to their unique luminescence and tumor-targeting properties. In this review, we have discussed applications of UCNPs in drug and gene delivery, photothermal therapy (PTT), photodynamic therapy (PDT) and tumor targeting in breast cancer. Further, present challenges and future opportunities for UCNPs in breast cancer treatment have also been mentioned.

Photoluminescent inorganic nanoprobe-based pathogen detection

Pathogens are serious threats to human health, and traditional detection techniques suffer from various limitations. The unique optical properties of photoluminescent inorganic nanomaterials, such as high photoluminescence quantum yields, good photostability, and tunable spectrum, make them ideal tools for the detection of pathogens with high specificity and sensitivity. In this review, the design strategies, working mechanisms, and applications of photoluminescent inorganic nanomaterial-based probes in pathogen detection are introduced. In particular, the design and construction of stimuli-responsive nanoprobes and their potential in these fields are highlighted.

Biosensors for the detection of Mycobacterium tuberculosis: a comprehensive overview

Tuberculosis (TB) infection is one of the leading causes of death in the world. According to WHO reports 2019, the average rate of decrease in global TB incidences was only 1.6% per year from 2000 to 2018, besides that the global decline in TB deaths was just 11%. Therefore, the dire need for early detection of the pathogen for the successful diagnosis of TB seems justified. Mycobacterium tuberculosis secretory proteins have gained more attention as TB biomarkers, for the early diagnosis and treatment of TB. Here in this review, we elaborate on the recent advancements made in the field of piezoelectric, magnetic, optical, and electrochemical biosensors, in addition to listing their merits and setbacks. Additionally, this review also discusses the construction of biosensors through modern integrated technologies, such as combinations of analytical chemistry, molecular biology, and nanotechnology. Integrated technologies enhance the detection for perceiving highly selective, specific, and sensitive signals to detect M. tuberculosis. Furthermore, this review highlights the recent challenges and scope of improvement in numerous biosensors developed for rapid, specific, selective, and sensitive detection of tuberculosis to reduce the TB burden and successful treatment.

Luminescent Nanomaterials (II)

In this review, we focus on sensing techniques and biological applications of various luminescent nanoparticles including quantum dot (QD), up-conversion nanoparticles (UCNPs) following the previous chapter. Fluorescent phenomena can be regulated or shifted by interaction between biological targets and luminescence probes depending on their distance, which is so-called Fӧrster resonance energy transfer (FRET). QD-based FRET technique, which has been widely applied as a bioanalytical tool, is described. We discuss time-resolved fluorescence (TRF) imaging and flow cytometry technique, using photoluminescent nanoparticles with unique properties for effectively improving selectivity and sensitivity. Based on these techniques, bioanalytical and biomedical application, bioimaging with QD, UCNPs, and Euripium-activated luminescent nanoprobes are covered. Combination of optical property of these luminescent nanoparticles with special functions such as drug delivery, photothermal therapy (PTT), and photodynamic therapy (PDT) is also described.

Sensors/nanosensors based on upconversion materials for the determination of pharmaceuticals and biomolecules: An overview

Upconversion materials have been the focus of a large body of research in analytical and clinical fields in the last two decades owing to their ability to convert light between various spectral regions and their particular photophysical features. They emit efficient and sharp ultraviolet (UV) or visible luminescence after excitation with near-infrared (NIR) light. These features overcome some of the disadvantages reported for conventional fluorescent materials and provide opportunities for high sensitivity chemo-and bio-sensing. Here, we review studies that used upconversion materials as sensors for the determination of pharmaceuticals and biomolecules in the last two decades. The articles included in this review were retrieved from the SCOPUS database using the search phrases: "upconversion nanoparticles for determination of pharmaceutical compounds", and "upconversion nanoparticles for determination of biomolecules". Details of each developed upconversion nanoparticles based sensor along with their relevant analytical parameters are reported and carefully explained.

A Novel Theranostic Nanoprobe for In Vivo Singlet Oxygen Detection and Real-Time Dose-Effect Relationship Monitoring in Photodynamic Therapy

Singlet oxygen, as the main member of reactive oxygen species, plays a significant role in cancer photodynamic therapy. However, the in vivo real-time detection of singlet oxygen remains challenging. In this work, a Förster resonance energy transfer (FRET)-based upconversion nanoplatform for monitoring the singlet oxygen in living systems is developed, with the ability to evaluate the in vivo dose-effect relationship between singlet oxygen and photodynamic therapy (PDT) efficacy. In details, this nanoplatform is composed of core-shell upconversion nanoparticles (UCNPs), photosensitizer MC540, NIR dye IR-820, and poly(acryl amine) PAA-octylamine, where the UCNPs serve as an energy donor while IR-820 serves as an energy acceptor. The nanoparticles are found to sensitively reflect the singlet oxygen levels generated in the tumor tissues during PDT, by luminescence intensity changes of UNCPs at 800 nm emission. Furthermore, it could also enable tumor treatment with satisfactory biocompatibility. To the best knowledge, this is the first report of a theranostic nanoplatform with the ability to formulate the in vivo dose-effect relationship between singlet oxygen and PDT efficacy and to achieve tumor treatment at the same time. This work might also provide an executable strategy to evaluate photodynamic therapeutic efficacy based on singlet oxygen pathway.

Aptamer and nanomaterial based FRET biosensors: a review on recent advances (2014-2019)

Fluorescence resonance energy transfer, one of the most powerful phenomena for elucidating molecular interactions, has been extensively utilized as a biosensing tool to provide accurate information at the nanoscale. Numerous aptamer- and nanomaterial-based FRET bioassays has been developed for detection of a large variety of molecules. Affinity probes are widely used in biosensors, in which aptamers have emerged as advantageous biorecognition elements, due to their chemical and structural stability. Similarly, optically active nanomaterials offer significant advantages over conventional organic dyes, such as superior photophysical properties, large surface-to-volume ratios, photostability, and longer shelf life. In this report (with 175 references), the use of aptamer-modified nanomaterials as FRET couples is reviewed: quantum dots, upconverting nanoparticles, graphene, reduced graphene oxide, gold nanoparticles, molybdenum disulfide, graphene quantum dots, carbon dots, and metal-organic frameworks. Tabulated summaries provide the reader with useful information on the current state of research in the field. Graphical abstract Schematic representation of a fluorescence resonance energy transfer-based aptamer nanoprobe in the absence and presence of a given target molecule (analyte). Structures are not drawn to their original scales.

Nicking enzyme-assisted signal-amplifiable Hg2+ detection using upconversion nanoparticles

A highly specific and sensitive isothermal method for mercury detection using DNA-conjugated upconversion nanoparticles is reported. A single-stranded DNA containing thymine bases, used as the Hg²⁺-capturing element through the formation of thymine-Hg²⁺-thymine complex, is covalently attached to the NaYF₄: Yb^3+, Tm³⁺ nanoparticles. Luminescence resonance energy transfer takes place between the NaYF₄: Yb^3+, Tm³⁺ nanoparticles as donor and DNA-intercalating SYBR Green I as the acceptor upon excitation of 980 nm. The sensitivity and selectivity toward Hg²⁺ are enhanced using the nicking enzyme, Nt. Alwl, which leads to signal amplification. By monitoring the ratio of acceptor emission to a reference peak, the presence of Hg²⁺ ions are quantitatively determined with a lower detection limit of 0.14 nM, which is much lower than the US Environmental Protection Agency (EPA) limit of Hg²⁺ in drinking water.

Lighting Up MicroRNA in Living Cells by the Disassembly of Lock-Like DNA-Programmed UCNPs-AuNPs through the Target Cycling Amplification Strategy

Intracellular microRNAs imaging based on upconversion nanoprobes has great potential in cancer diagnostics and treatments. However, the relatively low detection sensitivity limits their application. Herein, a lock-like DNA (LLD) generated by a hairpin DNA (H1) hybridizing with a bolt DNA (bDNA) sequence is designed, which is used to program upconversion nanoparticles (UCNPs, NaYF₄ @NaYF₄ :Yb, Er@NaYF₄ ) and gold nanoparticles (AuNPs). The upconversion emission is quenched through luminescence resonance energy transfer (LRET). The multiple LLD can be repeatedly opened by one copy of target microRNA under the aid of fuel hairpin DNA strands (H2) to trigger disassembly of AuNPs from the UCNP, resulting in the lighting up of UCNPs with a high detection signal gain. This strategy is verified using microRNA-21 as model. The expression level of microRNA-21 in various cells lines can be sensitively measured in vitro, meanwhile cancer cells and normal cells can be easily and accurately distinguished by intracellular microRNA-21 imaging via the nanoprobes. The detection limit is about 1000 times lower than that of the previously reported upconversion nanoprobes without signal amplification. This is the first time a nonenzymatic signal amplification method has been combined with UCNPs for imaging intracellular microRNAs, which has great potential for cancer diagnosis.

808 nm-light-excited upconversion nanoprobe based on LRET for the ratiometric detection of nitric oxide in living cancer cells

NO (nitric oxide) has dual functions in cancer, promoting carcinogenesis in low concentrations and inducing tumor cell apoptosis at high concentrations. The dual-edged-sword functions of NO make it particularly appealing to develop a sensitive and specific chemical probe for its detection. However, most NO sensors suffer from poor Stokes shifts and are limited by ultraviolet (UV) or visible light excitation, which render it difficult to avoid the intrinsic background signal. In this study, an 808 nm laser-excited Nd³⁺-sensitized upconversion nanoprobe based on LRET (luminescence resonance energy-transfer) for NO detection was constructed for the first time. This probe was composed of Nd³⁺-sensitized core-shell upconversion nanoparticles (540 nm and 660 nm emission) as the energy donor and RhBs as the acceptor. In the presence of NO, RhBs was converted into Rhodamine B and its strong absorption subsequently quenched the 540 nm fluorescence of UCNPs, while the emission at 660 nm remained constant. The ratiometric detection of the fluorescence at 540 nm, as compared to 660 nm, can precisely respond to the difference in NO levels with a detection limit of 0.21 μM. Importantly, compared with conventional UCNPs excited at 980 nm, the 808 nm light excitation led to lower water absorption and deeper tissue penetration, thus avoiding overheating and allowing for long-term biological imaging. This strategy has been perfectly applied to detecting the NO levels in living cells to differentiate the tumor cells from normal cells based on varied intracellular NO concentration. Further, the nanosystem realized the real-time monitoring of NO during treatment with NO donor drugs, which could inspire the future application of this probe to guide NO therapy.

A Universal Upconversion Sensing Platform for the Sensitive Detection of Tumour-Related ncRNA through an Exo III-Assisted Cycling Amplification Strategy

Here, a sensitive and universal noncoding RNA (ncRNA) upconversion sensing nanoplatform is developed. Gold nanoparticles bearing one hairpin DNA (Hp) molecule are conjugated to the linker DNA modified NaYF₄ :Yb, Er@NaYF₄ upconversion nanoparticles by DNA hybridization, leading to quenching of the upconversion emission through fluorescence resonance energy transfer. A signal DNA (SDNA) sequence is designed to open Hp, recovering the upconversion emission. To achieve universality and high sensitivity of the nanoprobe, an exonuclease III (Exo III)-assisted cycling amplification strategy is introduced. A multifunctional hairpin DNA (mHp) containing ncRNA recognition sequence and SDNA sequence is designed to recognize ncRNA and trigger Exo III as a biocatalyst to stepwise disintegrate itself, releasing both ncRNA and SDNA. The released ncRNA can be reused to release more SDNA, which greatly improves the sensing sensitivity. By changing the recognition portion of mHp, various ncRNA can be detected. The sensitive detection of both homeobox (HOX) transcript antisense RNA segment and miR-21 is achieved with this novel strategy, even in human serum, indicating the universality and sensitivity of the proposed strategy. Additionally, the expression level of miR-21 in human breast cancer cell (MCF-7) lysate is successfully measured, suggesting its potential in clinical diagnosis.

Nanodiagnostics for tuberculosis detection

INTRODUCTION

Tuberculosis (TB) is a leading killer worldwide. End TB strategy aims at ending the TB epidemic by 2030. Early, accurate, and affordable diagnosis represents a cornerstone to achieve this goal. Innovative strategies for TB diagnostics have been introduced. However, the ideal assay is yet unavailable and conventional methods remain necessary for diagnosis. Unique properties of nanoparticles (NPs) have allowed their utilization in TB detection via targeting disease biomarkers. Area covered: Until now, around thirty-five TB NP-based assays have been partially or fully characterized. Accuracy, low-cost, and short time-to-result represent the common properties of proposed platforms. TB nanodiagnostics now encompass almost all clinical aspects of the disease including active TB, non-tuberculous mycobacteria, rifampicin resistant TB, TB/HIV co-infection, latent TB, and extra-pulmonary TB. This review summarizes state-of-the-art knowledge of TB nanodiagnostics for the last 10 years. Special consideration is given for fabrication concepts, detection strategies, and clinical performance using various clinical specimens. The potential of TB nanodiagnostics to fulfill the need for ideal MTB testing is assessed. Expert commentary: TB nanodiagnostics show promise to be ideal detection tools that can meet the rigorous demands to end the TB epidemic by 2030.

Multiplex detection of extensively drug resistant tuberculosis using binary deoxyribozyme sensors

Current diagnostic tools for Mycobacterium tuberculosis (Mtb) have many disadvantages including low sensitivity, slow turnaround times, or high cost. Accurate, easy to use, and inexpensive point of care molecular diagnostic tests are urgently needed for the analysis of multidrug resistant (MDR) and extensively drug resistant (XDR) Mtb strains that emerge globally as a public health threat. In this study, we established proof-of-concept for a novel diagnostic platform (TB-DzT) for Mtb detection and the identification of drug resistant mutants using binary deoxyribozyme sensors (BiDz). TB-DzT combines a multiplex PCR with single nucleotide polymorphism (SNP) detection using highly selective BiDz sensors targeting loci associated with species typing and resistance to rifampin, isoniazid and fluoroquinolone antibiotics. Using the TB-DzT assay, we demonstrated accurate detection of Mtb and 5 mutations associated with resistance to three anti-TB drugs in clinical isolates. The assay also enables detection of a minority population of drug resistant Mtb, a clinically relevant scenario referred to as heteroresistance. Additionally, we show that TB-DzT can detect the presence of unknown mutations at target loci using combinatorial BiDz sensors. This diagnostic platform provides the foundation for the development of cost-effective, accurate and sensitive alternatives for molecular diagnostics of MDR- and XDR-TB.

The application of IS6110-baced loop-mediated isothermal amplification (LAMP) in the early diagnosis of tuberculous meningitis

Here, we evaluated the potential activity of rapid Mycobacterium tuberculosis detection with loop-mediated isothermal amplification (LAMP), for the early diagnosis of tuberculous meningitis (TBM). Patients with suspected TBM from January 2014 to December 2015 were reviewed retrospectively. The cerebrospinalfluid(CSF) was collected. Acid-fast bacillus (AFB) staining, MGIT 960 culture, real-time fluorescent quantitative polymerase chain reaction (RTFQ PCR) and LAMP were performed. A total of 200 patients were included in the study. Of which, 172 of them were diagnosed with TBM (86.00%). The sensitivities of AFB staining, MGIT 960 culture, LAMP and RTFQ PCR for TBM diagnosis were 2.91% (5/172), 12.79% (22/172), 43.02% (74/172), and 34.30% (59/172), respectively. The sensitivity of LAMP for TBM was significantly higher than those of AFB staining and MGIT960 culture (χ2 = 75.11, P < 0.001; χ2 = 43.88, P = 0.002). LAMP's sensitivity was however comparable to RTFQ PCR assay (χ2 = 2.08, P = 0.130). The specificity, positive predictive value and negative predictive value of LAMP in the diagnosis of TBM were 92.86% (26/28), 97.37% (74/76) and 20.97 % (26/124), respectively. The overall consistency between LAMP and RTFQ PCR in the diagnosis of TBM was 88.5% (177/200), with Kappa value of 0.870. The consistency between LAMP and MGIT960 culture was 71% (142/200), with Kappa value of 0.730. Among all the methods, LAMP had high sensitivity, specificity and positive predictive value, showing high consistency with MGIT960 culture and RTFQ PCR.

A Broadly Applicable Assay for Rapidly and Accurately Quantifying DNA Surface Coverage on Diverse Particles

DNA-modified particles are used extensively for applications in sensing, material science, and molecular biology. The performance of such DNA-modified particles is greatly dependent on the degree of surface coverage, but existing methods for quantitation can only be employed for certain particle compositions and/or conjugation chemistries. We have developed a simple and broadly applicable exonuclease III (Exo III) digestion assay based on the cleavage of phosphodiester bonds-a universal feature of DNA-modified particles-to accurately quantify DNA probe surface coverage on diverse, commonly used particles of different compositions, conjugation chemistries, and sizes. Our assay utilizes particle-conjugated, fluorophore-labeled probes that incorporate two abasic sites; these probes are hybridized to a complementary DNA (cDNA) strand, and quantitation is achieved via cleavage and digestion of surface-bound probe DNA via Exo III's apurinic endonucleolytic and exonucleolytic activities. The presence of the two abasic sites in the probe greatly speeds up the enzymatic reaction without altering the packing density of the probes on the particles. Probe digestion releases a signal-generating fluorophore and liberates the intact cDNA strand to start a new cycle of hybridization and digestion, until all fluorophore tags have been released. Since the molar ratio of fluorophore to immobilized DNA is 1:1, DNA surface coverage can be determined accurately based on the complete release of fluorophores. Our method delivers accurate, rapid, and reproducible quantitation of thiolated DNA on the surface of gold nanoparticles, and also performs equally well with other conjugation chemistries, substrates, and particle sizes, and thus offers a broadly useful assay for quantitation of DNA surface coverage.

Self-assembly of an upconverting nanocomplex and its application to turn-on detection of metalloproteinase-9 in living cells

Upcoversion nanoparticles are an emerging luminescent nanomaterial with excellent photophysical properties that have great benefits in biological sensing. In this study, a luminescent turn-on biosensor for cell-secreted protease activity assay is established based on resonance energy transfer in an upconversion nanoparticle-graphene oxide nano-assembly. The proposed biosensor consists of a blue-emitting upconversion nanoparticle covered with a quenching complex, comprising gelatin as the proteinase substrate and graphene oxide nanosheets as luminescence acceptors. After enzymatic digestion, the upconversion nanoparticles lose the gelatin cover due to the disassembly of the quenching complex, thus the upconverting luminescence in the blue region is restored (a turn-on response). The recovered upconverting luminescence is proportional to the protease concentration; the limit of detection was 12 ng ml(-1). Finally, the upconversion-graphene oxide nanocomplex was successfully applied in the detection of cell-secreted protease-metalloproteinase in MCF-7 cancer cells with high sensitivity and specificity.

Upconversion Nanoparticle-Based Förster Resonance Energy Transfer for Detecting DNA Methylation

Aberrant methylation of a crucial CpG island is the main mechanism for the inactivation of CDKN2A in the early stages of carcinogenesis. Therefore, the detection of DNA methylation with high sensitivity and specificity is important, and various detection methods have been developed. Recently, upconversion nanoparticles (UCNPs) have been found to display a high signal-to-noise ratio and no photobleaching, making them useful for diagnostic applications. In this pilot study, we applied UCNPs to the detection of CDKN2A methylation and evaluated the feasibility of this system for use in molecular diagnostics. DNA PCR was performed using biotinylated primers, and the PCR amplicon was then intercalated with SYTOX Orange dye, followed by incubation with streptavidin-conjugated UCNPs. Fluorescence detection of the Förster resonance energy transfer (FRET) of the UCNPs (MS-UC-FRET) was then performed, and the results were compared to those from real-time PCR (RQ-PCR) and pyrosequencing. Detection by MS-UC-FRET was more sensitive than that by either RQ-PCR or pyrosequencing. Our results confirmed the success of our MS-UC-FRET system for detecting DNA methylation and demonstrated the potential application of this system in molecular diagnostics.

Simple Detection of the IS6110 Sequence of Mycobacterium tuberculosis Complex in Sputum, Based on PCR with Graphene Oxide

Graphene oxide (GO) has proven to be a satisfactory DNA-sensor platform for applications in enzyme-free signal amplification, fluorescence-based amplification, and nanoparticle-based platforms because of its excellent electrical, thermal, and optical properties. In this study, we designed a novel platform for the fluorescence detection of biomolecules, using a fluorescent dye-labeled primer and GO. We applied this system for the detection of the IS6110 insertion sequence of the Mycobacterium tuberculosis complex (MTB) and evaluated its feasibility for use in molecular diagnostics. Fifty-four sputum specimens were collected at our institution from October 2010 to March 2012. To detect MTB in the samples, we performed PCR amplification of the IS6110 DNA sequence using FAM-labeled primers, after which the PCR amplicon was incubated with GO and the fluorescence was measured. The results were compared with those obtained by conventional real-time quantitative PCR (RQ-PCR). The fluorescence intensity observed increased in a concentration-dependent manner with the FAM-labeled IS6110 amplicon. The results of the PCR-GO system for detecting IS6110 DNA were in good agreement with those obtained with conventional RQ-PCR (kappa statistic = 0.925). The PCR-GO system detected MTB DNA in 23 of 25 RQ-PCR-positive sputum samples (92.0%; 95% CI, 75.0–98.0%), but not in 29 of 29 RQ-PCR-negative sputum samples (100%; 95% CI, 88.1–100.0%). These results indicate the utility of the PCR-GO system in molecular diagnostics.

Interplay between Static and Dynamic Energy Transfer in Biofunctional Upconversion Nanoplatforms

Clarification of the energy-transfer (ET) mechanism is of vital importance for constructing efficient upconversion nanoplatforms for biological/biomedical applications. Yet, most strategies of optimizing these nanoplatforms were casually based on a dynamic ET assumption. In this work, we have modeled quantitatively the shell-thickness-dependent interplay between dynamic and static ET in nanosystems and validated the model in a typical biofunctional upconversion nanoplatform composed of NaYF4:Er, Yb/NaYF4 upconversion nanoparticles (UCNPs), and energy-acceptor photosensitizing molecule Rose Bengal (RB). It was determined that with a proper thickness shell, the energy transferred via dynamic ET as well as static ET in this case could be significantly improved by ∼4 and ∼9 fold, respectively, compared with the total energy transferred from bare core UCNPs. Our results shall form the bedrock in designing highly efficient ET-based biofunctional nanoplatforms.

Lanthanide-doped upconversion nano-bioprobes: electronic structures, optical properties, and biodetection

The latest advances in lanthanide-doped upconversion nanoparticles were comprehensively reviewed, which covers from their fundamental photophysics to biodetection.

Nanoparticle based fluorescence resonance energy transfer (FRET) for biosensing applications

Nanoparticle based FRET assays have higher energy transfer efficiency and better performance compared with traditional organic fluorophore based FRET assays.

An upconversion nanocomposite for fluorescence resonance energy transfer based cholesterol-sensing in human serum

Upconversion nanophosphors (UCNPs) are extremely useful for analytical applications, since they display a high signal-to-noise ratio, and their photobleaching can be ignored. Herein, a novel upconversion nanocomposite composed of β-cyclodextrin (β-CD) derivative modified UCNPs and rhodamine B (RB) was prepared for the detection of cholesterol (Cho). The upconversion luminescence (UCL) emission can serve as a Cho-sensing signal by an effective fluorescence resonance energy transfer (FRET) process, using UCNPs as the donor and RB as the quencher. The sensor for Cho detection in human serum shows excellent sensitivity and selectivity, which has the potential for clinical applications in the analysis of other biological and environmental samples.