Fluorescence Detection of H5N1 Virus Gene Sequences Based on Optical Tweezers with Two-Photon Excitation Using a Single Near Infrared Nanosecond Pulse Laser

Using time-shared scanning optical tweezers assisted two-photon fluorescence imaging to establish a versatile CRISPR/Cas12a-mediated biosensor

Based on the admirable precision to identify target nucleic acids and the particular trans-cleavage feature, CRISPR/Cas12a system is a useful means to further improve the sensing accuracy and the design flexibility of fluorescence biosensors. However, the current construction concepts still suffer from insufficient sensitivity, unsuitable for complicated real samples and limited detection species. In this work, much efforts are achieved to address these obstacles. At first, we adopt a microsphere sustained signal enrichment, under which a home-made time-shared scanning optical tweezers assisted fluorescence imaging is employed to guarantee a stable excitation and also realize multiflux measurement. Furthermore, by taking advantage of the low background merit of the near-infrared light excited two-photon fluorescence, a commendable anti-interference capability is endowed to operate in complex media. After utilizing a functional DNA (e.g. aptamer and DNAzyme) regulated mediation pathway to respond non-nucleic acid analytes (alpha fetal protein and Pb²⁺), the newly-established CRISPR/Cas12a-mediated fluorescence biosensor is found to display favorable assay performance. More importantly, our analytical methodology can act as a versatile and reliable toolbox in various applications such as disease diagnosis and environmental analysis, propelling the development of CRISPR system in biosensing field.

Optical trapping and fluorescence control with vectorial structured light

Here we functionalized micro-scaled polymer beads with nano-scaled quantum dots and demonstrate optical trapping and tweezing, with in-situ fluorescence measurement, in an all-digital all-optical configuration. We outline the chemistry required to facilitate this, from deactivating the optical trapping environment to size, adhesion and agglomeration control. We introduce a novel holographic optical trapping set-up that leverages on vectorially structured light, allowing for the delivery of tuneable forms of light from purely scalar to purely vector, including propagation invariant flat-top beams for uniform illumination and tailored intensity gradient landscapes. Finally, we show how this has the potential to quench bleaching in a single wavelength trap by linear (spatial mode) rather than non-linear effects, advancing the nascent field of optics for chemistry.

Two-Photon Fluorescence in Red and Violet Conjugated Polymer Microspheres

We investigate the two-photon fluorescence (TPF) of conjugated polymer (CP) microspheres with diameters up to tens of micrometers. Two polymers, emitting in either the violet or red, were first synthesized and characterized in terms of their one-photon fluorescence and three-dimensional internal microstructure. Under femtosecond infrared excitation, both types of microspheres showed a strong TPF, which was investigated by the excitation intensity dependence, emission spectroscopy, time-resolved luminescence, and photobleaching dynamics. While the violet-fluorescent microspheres performed similarly compared to dye-doped polystyrene counterparts emitting at a similar wavelength, the red-fluorescent microspheres showed a two-orders-of-magnitude stronger TPF. This excellent performance is attributed to enhanced hyperpolarizability associated with intermolecular interactions in the polymer solid, indicating a route toward designed CP microspheres that could outperform currently-available microparticles for sensing or imaging applications involving two-photon fluorescence.

Holographic Optical Tweezers and Boosting Upconversion Luminescent Resonance Energy Transfer Combined Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)/Cas12a Biosensors

Taking advantage of outstanding precision in target recognition and trans-cleavage ability, the recently discovered CRISPR/Cas12a system provides an alternative opportunity for designing fluorescence biosensors. To fully exploit the analytical potential, we introduce here some meaningful concepts. First, the collateral cleavage of CRISPR/Cas12a is efficiently activated in a functional DNA regulation manner and the bottleneck which largely applicable to nucleic acids detection is broken. After selection of a representative aptamer and DNAzyme as the transduction pathways, the sensing coverage is extended to a small organic compound (ATP) and a metal ion (Na⁺). The assay sensitivity is significantly improved by utilizing a bead-supported enrichment strategy wherein emerging holographic optical tweezers are used to enhance imaging stability and simultaneously achieve multiflux analysis. Last, a sandwich-structured energy-concentrating upconversion nanoparticle triggered boosting luminescent resonance energy transfer mode is comined to face with complicated biological samples by skillfully confining the emitters into a very limited inner shell. Following the above attempts, the developed CRISPR/Cas12a biosensors not only present an ultrasensitive assay behavior toward these model non-nucleic acid analytes but also can serve as a formidable toolbox for determining real samples including single cell lysates and human plasma, proving a good practical application capacity.

Two-Photon Fluorescent Nanomaterials and Their Applications in Biomedicine

In recent years, two-photon excited (TPE) materials have attracted great attentions because of their excellent advantages over conventional one-photon excited (OPE) materials, such as deep tissue penetration, three-dimensional spatial selectivity and low phototoxicity. Also, they have been widely applied in lots of field, such as biosensing, imaging, photo-catalysis, photoelectric conversion, and therapy. In this article, we review recent advances in vibrant topic of two-photon fluorescent nanomaterials, including organic molecules, quantum dots (QDs), carbon dots (CDs) and metal nanoclus-ters (MNCs). The optical properties, synthetic methods and important applications of TPE nanomaterials in biomedical field, such as biosensing, imaging and therapy are introduced. Also, the probable challenges and perspectives in the forthcoming development of two-photon fluorescent nanomaterials are addressed.

On-Chip Optical Detection of Viruses: A Review

The current outbreak of the coronavirus disease-19 (COVID-19) pandemic worldwide has caused millions of fatalities and imposed a severe impact on our daily lives. Thus, the global healthcare system urgently calls for rapid, affordable, and reliable detection toolkits. Although the gold-standard nucleic acid amplification tests have been widely accepted and utilized, they are time-consuming and labor-intensive, which exceedingly hinder the mass detection in low-income populations, especially in developing countries. Recently, due to the blooming development of photonics, various optical chips have been developed to detect single viruses with the advantages of fast, label-free, affordable, and point of care deployment. Herein, optical approaches especially in three perspectives, e.g., flow-free optical methods, optofluidics, and surface-modification-assisted approaches, are summarized. The future development of on-chip optical-detection methods in the wave of emerging new ideas in nanophotonics is also briefly discussed.

Detecting Biothreat Agents: From Current Diagnostics to Developing Sensor Technologies

Although a fundamental understanding of the pathogenicity of most biothreat agents has been elucidated and available treatments have increased substantially over the past decades, they still represent a significant public health threat in this age of (bio)terrorism, indiscriminate warfare, pollution, climate change, unchecked population growth, and globalization. The key step to almost all prevention, protection, prophylaxis, post-exposure treatment, and mitigation of any bioagent is early detection. Here, we review available methods for detecting bioagents including pathogenic bacteria and viruses along with their toxins. An introduction placing this subject in the historical context of previous naturally occurring outbreaks and efforts to weaponize selected agents is first provided along with definitions and relevant considerations. An overview of the detection technologies that find use in this endeavor along with how they provide data or transduce signal within a sensing configuration follows. Current "gold" standards for biothreat detection/diagnostics along with a listing of relevant FDA approved in vitro diagnostic devices is then discussed to provide an overview of the current state of the art. Given the 2014 outbreak of Ebola virus in Western Africa and the recent 2016 spread of Zika virus in the Americas, discussion of what constitutes a public health emergency and how new in vitro diagnostic devices are authorized for emergency use in the U.S. are also included. The majority of the Review is then subdivided around the sensing of bacterial, viral, and toxin biothreats with each including an overview of the major agents in that class, a detailed cross-section of different sensing methods in development based on assay format or analytical technique, and some discussion of related microfluidic lab-on-a-chip/point-of-care devices. Finally, an outlook is given on how this field will develop from the perspective of the biosensing technology itself and the new emerging threats they may face.

Chiral MoS2 Quantum Dots: Dual-Mode Detection Approaches for Avian Influenza Viruses

Molybdenum disulfide (MoS2), a type of transition metal dichalcogenide material, has emerged as an important class among 2D systems. When 2D MoS2 materials are reduced to 0D quantum dots (QDs), they introduce new optical properties that point to several potential technological advantages in electronic, magnetic, optical, and catalytic properties. In this study, a simple way to produce chiral MoS2 QDs from MoS2 nanopowder is presented using l(+)-ascorbic acid as a reducing agent. The calculated quantum yield of QDs is 11.06%. Experimental results reveal that the size of QDs is uniformly monodispersed (2-3 nm) and have a blue emissive fluorescence peak and circular dichroism (CD) peak located at 420 and 330 nm, respectively. Furthermore, a dual-mode detection system based on fluorescence and chirality is performed using as-synthesized MoS2 QDs, where QDs are conjugated with anti-hemagglutinin antibodies of avian influenza virus and made into an immunobridge in the presence of target virus and anti-neuraminidase antibodies conjugated magnetic nanoparticles (MNPs). The photoluminescence and CD spectra of unconjugated QDs after separated magnetochirofluorescent (MNPs-QDs) nanohybrids by external magnets enables influenza virus A (H5N1) detection with the limit of detection value of 7.35 and 80.92 pg mL-1, respectively.

A Nanostructured Microfluidic Immunoassay Platform for Highly Sensitive Infectious Pathogen Detection

Rapid and simultaneous detection of multiple potential pathogens by portable devices can facilitate early diagnosis of infectious diseases, and allow for rapid and effective implementation of disease prevention and treatment measures. The development of a ZnO nanorod integrated microdevice as a multiplex immunofluorescence platform for highly sensitive and selective detection of avian influenza virus (AIV) is described. The 3D morphology and unique optical property of the ZnO nanorods boost the detection limit of the H5N2 AIV to as low as 3.6 × 103 EID50 mL-1 (EID50 : 50% embryo infectious dose), which is ≈22 times more sensitive than conventional enzyme-linked immunosorbent assay. The entire virus capture and detection process could be completed within 1.5 h with excellent selectivity. Moreover, this microfluidic biosensor is capable of detecting multiple viruses simultaneously by spatial encoding of capture antibodies. One prominent feature of the device is that the captured H5N2 AIV can be released by simply dissolving ZnO nanorods under slightly acidic environment for subsequent off-chip analyses. As a whole, this platform provides a powerful tool for rapid detection of multiple pathogens, which may extent to the other fields for low-cost and convenient biomarker detection.

Paper microchip with a graphene-modified silver nano-composite electrode for electrical sensing of microbial pathogens

Rapid and sensitive point-of-care diagnostics are of paramount importance for early detection of infectious diseases and timely initiation of treatment. Here, we present cellulose paper and flexible plastic chips with printed graphene-modified silver electrodes as universal point-of-care diagnostic tools for the rapid and sensitive detection of microbial pathogens or nucleic acids through utilizing electrical sensing modality and loop-mediated isothermal amplification (LAMP). We evaluated the ability of the developed paper-based assay to detect (i) viruses on cellulose-based paper microchips without implementing amplification in samples with viral loads between 106 and 108 copies per ml, and (ii) amplified HIV-1 nucleic acids in samples with viral loads between 10 fg μl-1 and 108 fg μl-1. The target HIV-1 nucleic acid was amplified using the RT-LAMP technique and detected through the electrical sensing of LAMP amplicons for a broad range of RNA concentrations between 10 fg μl-1 and 108 fg μl-1 after 40 min of amplification time. Our assay may be used for antiretroviral therapy monitoring where it meets the sensitivity requirement of the World Health Organization guidelines. Such a paper microchip assay without the amplification step may also be considered as a simple and inexpensive approach for acute HIV detection where maximum viral replication occurs.

Self-assembled star-shaped chiroplasmonic gold nanoparticles for an ultrasensitive chiro-immunosensor for viruses

Nanoengineered chiral gold nanoparticles and quantum dots for ultrasensitive chiroptical sensing of viruses in blood samples.

Silver Nanoclusters Beacon as Stimuli-Responsive Versatile Platform for Multiplex DNAs Detection and Aptamer-Substrate Complexes Sensing

An activatable silver nanoclusters beacon (ASNCB) was synthesized through a facile one-pot approach and applied for multiplex DNAs, small molecule, and protein sensing. Multifunctional single-stranded DNA sequences are rationally designed and used for ASNCB in situ synthesis. Via target-responsive structure transformation of ASNCB, target recognition induced ASNCB conformational transition and lit up the fluorescent signal of silver nanoclusters. By further implementing two different color ASNCBs (520 and 600 nm), the parallel multiplexed analysis of two target genes (Influenza A virus genes H1N1 and H5N1) is achieved. Additionally, with the introduction of aptamer for the design of the molecular beacon, the detections of small molecule adenosine triphosphate (ATP) and biomacromolecule thrombin have also been realized. This is the first time that an activatable fluorescent silver nanoclusters (Ag NCs)-based probe and the target recognition have been integrated into a single process, which provides a versatile platform for different analytes in a facile way. The successful application of our proposed ASNCB in real sample analysis and ATP imaging in living cells further displayed its promising potential for fluorescence sensing.