Lateral flow (immuno)assays are currently used for qualitative, semiquantitative and to some extent quantitative monitoring in resource-poor or non-laboratory environments. Applications include tests on pathogens, drugs, hormones and metabolites in biomedical, phytosanitary, veterinary, feed/food and environmental settings. We describe principles of current formats, applications, limitations and perspectives for quantitative monitoring. We illustrate the potentials and limitations of analysis with lateral flow (immuno)assays using a literature survey and a SWOT analysis (acronym for “strengths, weaknesses, opportunities, threats”). Articles referred to in this survey were searched for on MEDLINE, Scopus and in references of reviewed papers. Search terms included “immunochromatography”, “sol particle immunoassay”, “lateral flow immunoassay” and “dipstick assay”.

https://link.springer.com/content/pdf/10.1007%2Fs00216-008-2287-2.pdf

Lateral flow (immuno)assay: its strengths, weaknesses, opportunities and threats. A literature survey.

Upconversion refers to non-linear optical processes that convert two or more low-energy pump photons to a higher-energy output photon. After being recognized in the mid-1960s, upconversion has attracted significant research interest for its applications in optical devices such as infrared quantum counter detectors and compact solid-state lasers. Over the past decade, upconversion has become more prominent in biological sciences as the preparation of high-quality lanthanide-doped nanoparticles has become increasingly routine. Owing to their small physical dimensions and biocompatibility, upconversion nanoparticles can be easily coupled to proteins or other biological macromolecular systems and used in a variety of assay formats ranging from bio-detection to cancer therapy. In addition, intense visible emission from these nanoparticles under near-infrared excitation, which is less harmful to biological samples and has greater sample penetration depths than conventional ultraviolet excitation, enhances their prospects as luminescent stains in bio-imaging. In this article, we review recent developments in optical biolabeling and bio-imaging involving upconversion nanoparticles, simultaneously bringing to the forefront the desirable characteristics, strengths and weaknesses of these luminescent nanomaterials.

Upconversion nanoparticles in biological labeling, imaging, and therapy

Lanthanide-doped upconversion nanoparticles (UCNPs) have attracted considerable interest due to their superior physicochemical features, such as large anti-Stokes shifts, low autofluorescence background, low toxicity and high penetration depth, which make them extremely suitable for use as alternatives to conventional downshifting luminescence bioprobes like organic dyes and quantum dots for various biological applications. A fundamental understanding of the photophysics of lanthanide-doped UCNPs is of vital importance for discovering novel optical properties and exploring their new applications. In this review, we focus on the most recent advances in the development of lanthanide-doped UCNPs as potential luminescent nano-bioprobes by means of our customized lanthanide photophysics measurement platforms specially designed for upconversion luminescence, which covers from their fundamental photophysics to bioapplications, including electronic structures (energy levels and local site symmetry of emitters), excited-state dynamics, optical property designing, and their promising applications for in vitro biodetection of tumor markers. Some future prospects and efforts towards this rapidly growing field are also envisioned.

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

The theory of image formation is formulated in terms of the coherence function in the object plane, the diffraction distribution function of the image-forming system and a function describing the structure of the object. There results a four-fold integral involving these functions, and the complex conjugate functions of the latter two. This integral is evaluated in terms of the Fourier transforms of the coherence function, the diffraction distribution function and its complex conjugate. In fact, these transforms are respectively the distribution of intensity in an 'effective source', and the complex transmission of the optical system-they are the data initially known and are generally of simple form. A generalized 'transmission factor' is found which reduces to the known results in the simple cases of perfect coherence and complete incoherence. The procedure may be varied in a manner more suited to non-periodic objects. The theory is applied to study inter alia the influence of the method of illumination on the images of simple periodic structures and of an isolated line.

On the diffraction theory of optical images

Despite a growing focus from the academic community, the field of microfluidics has yet to produce many commercial devices for point-of-care (POC) diagnostics. One of the main reasons for this is the difficulty in producing low-cost, sensitive, and portable optical detection systems. Although electrochemical methods work well for certain applications, optical detection is generally regarded as superior and is the method most widely employed in laboratory clinical chemistry. Conventional optical systems, however, are costly, require careful alignment, and do not translate well to POC devices. Furthermore, many optical detection paradigms such as absorbance and fluorescence suffer at smaller geometries because the optical path length through the sample is shortened. This review examines the innovative techniques which have recently been developed to address these issues. We highlight microfluidic diagnostic systems which demonstrate practical integration of sample preparation, analyte enrichment, and optical detection. We also examine several emerging detection paradigms involving nanoengineered materials which do not suffer from the same miniaturization disadvantages as conventional measurements.

Innovations in optical microfluidic technologies for point-of-care diagnostics

Up-converting phosphor technology (UPT)-based lateral-flow immunoassay has been developed for quantitative detection of Yersinia pestis rapidly and specifically. In this assay, 400 nm up-converting phosphor particles were used as the reporter. A sandwich immumoassay was employed by using a polyclonal antibody against F1 antigen of Y. pestis immobilized on the nitrocellulose membrane and the same antibody conjugated to the UPT particles. The signal detection of the strips was performed by the UPT-based biosensor that could provide a 980 nm IR laser to excite the phosphor particles, then collect the visible luminescence emitted by the UPT particles and finally convert it to the voltage as a signal. VT and VC stand for the multiplied voltage units for the test and the control line, respectively, and the ratio VT/VC is directly proportional to the number of Y. pestis in a sample. We observed a good linearity between the ratio and log CFU/ml of Y. pestis above the detection limit, which was approximately 104 CFU/ml. The precision of the intra- and inter-assay was below 15% (coefficient of variation, CV). Cross-reactivity with related Gram-negative enteric bacteria was not found. The UPT-LF immunoassay system presented here takes less than 30 min to perform from the sample treatment to the data analysis. The current paper includes only preliminary data concerning the biomedical aspects of the assay, but is more concentrated on the technical details of establishing a rapid manual assay using a state-of-the-art label chemistry.

/pdf/rapid-quantitative-detection-of-yersinia-pestis-by-lateral-1v97u10ji6.pdf

Rapid quantitative detection of Yersinia pestis by lateral-flow immunoassay and up-converting phosphor technology-based biosensor.

Development of an up-converting phosphor technology-based 10-channel lateral flow assay for profiling antibodies against Yersinia pestis

Provided is a measuring device and a calibration method for optical lens distortion. The measuring device comprises a single star light simulator, an adjusting rack, a to-be-tested lens, a CCD (charge coupled device) camera, a one-dimensional air flotation turntable, an angle encoder, a computer and an optical platform. The calibration method includes the steps of using a centroid localization algorithm to determine centroid position coordinates of a star point image when the to-be-tested lens is under different fields of view, establishing a calibration model for the to-be-tested lens distortion based on the distribution of the centroid position coordinates of the star point image under the entire field of view, and realizing the calibration of the distorted to-be-tested lens. The measuring device and the calibration method for the optical lens distortion has the advantages that the device is simple; the method is convenient; measurement accuracy is high; and the optical lens distortion can be easily measured and calibrated.

Measuring device and calibration method for optical lens distortion

A simple optical reader was developed for rapid and sensitive quantification of lateral flow (LF) strip with upconverting phosphor (UCP) particles as reporters. The excitation beam from a 980 nm laser diode (LD) was focused to a 4 mm (length) times 0.02 mm (width) rectangular spot on LF strip. A rectangular slit with 4 mm times 0.02 mm before the photomultiplier tube (PMT) which was selected as receiver was introduced as field diaphragm to prevent stray light from entering the PMT. The scanning resolution was 20 mum, and the scanning speed was 0.75 mm/s, and the scanning range was 10 mm. With the above optical reader, serial dilutions of Yersinia pestis F1 antigen were detected to achieve the test sensitivity was 5 ng/ml, and the dynamic range reached 150 ng/ml. The algorithms of the low-pass filter and the first derivative were used to search the boundaries of T line and C line from the original data acquired by the reader. A four-parameter logistic mathematical model was used to deduce the quantitative equation for determination of unknown F1 antigen concentration. Our 1-D optical reader possessed the following characteristics: high 1-D testing resolution, high sensitivity, simple structure, simple data processing method, high testing efficiency, and small total volume.

A Simple Optical Reader for Upconverting Phosphor Particles Captured on Lateral Flow Strip

Pixelated metasurfaces integrating both the functions of linear polarization and circular polarization filters on a single platform can achieve full-Stokes polarization detection At present, the pixelated full-Stokes metasurfaces mainly face the following problems: low transmission, low circular dichroism (CD) of circular polarization filters, and high requirements in fabrication and integration Herein, we propose high performance ultracompact all-dielectric pixelated full-Stokes metasurfaces in the near-infrared band based on silicon-on-insulator, which is compatible with the available semiconductor industry technologies Circular polarization filters with high CD are achieved by using simple two-dimensional chiral structures, which can be easily integrated with the linear polarization filters on a single chip In addition, the dielectric materials have higher transmission than metal materials with intrinsic absorption We experimentally demonstrated the circular polarization filter with maximum CD up to 70% at a wavelength of 16 μm and average transmission efficiency above 80% from 148 μm to 16 μm Therefore, our design is highly desirable for many applications, such as target detection, clinical diagnosis, and polarimetric imaging and sensing

/pdf/high-efficiency-all-dielectric-pixelated-metasurface-for-1azqgtiiuu.pdf

Huijie Huang

Papers

Rapid quantitative detection of Yersinia pestis by lateral-flow immunoassay and up-converting phosphor technology-based biosensor.

Development of an up-converting phosphor technology-based 10-channel lateral flow assay for profiling antibodies against Yersinia pestis

Measuring device and calibration method for optical lens distortion

A Simple Optical Reader for Upconverting Phosphor Particles Captured on Lateral Flow Strip

High efficiency all-dielectric pixelated metasurface for near-infrared full-Stokes polarization detection