Plasmonic and label-free real-time quantitative PCR for point-of-care diagnostics

Plasmonic-Driven Regulation of Biomolecular Activity In Situ

Selective and remote manipulation of activity for biomolecules, including protein, DNA, and lipids, is crucial to elucidate their molecular function and to develop biomedical applications. While advances in tool development, such as optogenetics, have significantly impacted these directions, the requirement for genetic modification significantly limits their therapeutic applications. Plasmonic nanoparticle heating has brought new opportunities to the field, as hot nanoparticles are unique point heat sources at the nanoscale. In this review, we summarize fundamental engineering problems such as plasmonic heating and the resulting biomolecular responses. We highlight the biological responses and applications of manipulating biomolecules and provide perspectives for future directions in the field.

FlashPCR: Revolutionising qPCR by Accelerating Amplification through Low ∆T Protocols

Versatility, sensitivity, and accuracy have made the real-time polymerase chain reaction (qPCR) a crucial tool for research, as well as diagnostic applications. However, for point-of-care (PoC) use, traditional qPCR faces two main challenges: long run times mean results are not available for half an hour or more, and the requisite high-temperature denaturation requires more robust and power-demanding instrumentation. This study addresses both issues and revises primer and probe designs, modified buffers, and low ∆T protocols which, together, speed up qPCR on conventional qPCR instruments and will allow for the development of robust, point-of-care devices. Our approach, called "FlashPCR", uses a protocol involving a 15-second denaturation at 79 °C, followed by repeated cycling for 1 s at 79 °C and 71 °C, together with high Tm primers and specific but simple buffers. It also allows for efficient reverse transcription as part of a one-step RT-qPCR protocol, making it universally applicable for both rapid research and diagnostic applications.

Assessing Different PCR Master Mixes for Ultrarapid DNA Amplification: Important Analytical Parameters

The basic principles of ultrafast plasmonic PCR have been promulgated in the scientific and technological literature for over a decade. Yet, its everyday diagnostic utility remains unvalidated in pre-clinical and clinical settings. Although the impressive speed of plasmonic PCR reaction is well-documented, implementing this process into a device form compatible with routine diagnostic tasks has been challenging. Here, we show that combining careful system engineering and process control with innovative and specific PCR biochemistry makes it possible to routinely achieve a sensitive and robust "10 min" PCR assay in a compact and lightweight system. The critical analytical parameters of PCR reactions are discussed in the current instrument setting.

Rapid quantitative PCR equipment using photothermal conversion of Au nanoshell

The emergence of infectious diseases worldwide necessitates rapid and precise diagnostics. Using gold nanoshells in the PCR mix, we harnessed their unique photothermal properties in the near-infrared regime to attain efficient heating, reaching ideal photothermal PCR cycle temperature profile. Our photothermal PCR method expedited DNA amplification while retaining its detection sensitivity. Combining photothermal quantitative PCR with real-time fluorometry and non-invasive temperature measurement, we could amplify the target DNA within just 25 min, with a minimum detectable DNA amount of 50 picograms. This innovation in photothermal qPCR, leveraging the photothermal properties of gold nanoshells, will pave the way for immediate point-of-care diagnostics of nucleic acid biomarkers.

A roadmap to high-speed polymerase chain reaction (PCR): COVID-19 as a technology accelerator

The limit of detection (LOD), speed, and cost of crucial COVID-19 diagnostic tools, including lateral flow assays (LFA), enzyme-linked immunosorbent assays (ELISA), and polymerase chain reactions (PCR), have all improved because of the financial and governmental support for the epidemic. The most notable improvement in overall efficiency among them has been seen with PCR. Its significance for human health increased during the COVID-19 pandemic, when it emerged as the commonly used approach for identifying the virus. However, because of problems with speed, complexity, and expense, PCR deployment in point-of-care settings continues to be difficult. Microfluidic platforms offer a promising solution by enabling the development of smaller, more affordable, and faster PCR systems. In this review, we delve into the engineering challenges associated with the advancement of high-speed microfluidic PCR equipment. We introduce criteria that facilitate the evaluation and comparison of factors such as speed, LOD, cycling efficiency, and multiplexing capacity, considering sample volume, fluidics, PCR reactor geometry and materials, as well as heating/cooling methods. We also provide a comprehensive list of commercially available PCR devices and conclude with projections and a discussion regarding the current obstacles that need to be addressed in order to progress further in this field.

Single-shot multi-channel plasmonic real-time polymerase chain reaction for multi-target point-of-care testing

Plasmonic nucleic acid amplification tests demand high-throughput and multi-target detection of infectious diseases as well as short turnaround time and small size for point-of-care molecular diagnostics. Here, we report a multi-channel plasmonic real-time reverse-transcription polymerase chain reaction (mpRT-qPCR) assay for ultrafast and on-chip multi-target detection. The mpRT-qPCR system features two pairs of plasmonic thermocyclers for rapid nanostructure-driven amplification and microlens array fluorescence microscopes for in situ multi-color fluorescence quantification. Each channel shows a physical dimension of 32 mm, 75 mm, and 25 mm in width, length, and thickness. The ultrathin microscopes simultaneously capture four different fluorescence images from two PCR chambers of a single cartridge at a single shot exposure per PCR cycle of four different excitation light sources. The experimental results demonstrate a single assay result of high-throughput amplification and multi-target quantification for RNA-dependent RNA polymerase, nucleocapsid, and human ribonuclease P genes in SARS-CoV-2 RNA detection. The mpRT-PCR increases the number of tests four times over the single RT-PCR and exhibits a short detection time of 15 min for the four RT-PCR reactions. This point-of-care molecular diagnostic platform can reduce false negative results in clinical applications of virus detection and decentralize healthcare facilities with limited infrastructure.

Photothermal Nanomaterials: A Powerful Light-to-Heat Converter

All forms of energy follow the law of conservation of energy, by which they can be neither created nor destroyed. Light-to-heat conversion as a traditional yet constantly evolving means of converting light into thermal energy has been of enduring appeal to researchers and the public. With the continuous development of advanced nanotechnologies, a variety of photothermal nanomaterials have been endowed with excellent light harvesting and photothermal conversion capabilities for exploring fascinating and prospective applications. Herein we review the latest progresses on photothermal nanomaterials, with a focus on their underlying mechanisms as powerful light-to-heat converters. We present an extensive catalogue of nanostructured photothermal materials, including metallic/semiconductor structures, carbon materials, organic polymers, and two-dimensional materials. The proper material selection and rational structural design for improving the photothermal performance are then discussed. We also provide a representative overview of the latest techniques for probing photothermally generated heat at the nanoscale. We finally review the recent significant developments of photothermal applications and give a brief outlook on the current challenges and future directions of photothermal nanomaterials.

Ultrafast Plasmonic Nucleic Acid Amplification and Real-Time Quantification for Decentralized Molecular Diagnostics

Point-of-care real-time reverse-transcription polymerase chain reaction (RT-PCR) facilitates the widespread use of rapid, accurate, and cost-effective near-patient testing that is available to the public. Here, we report ultrafast plasmonic nucleic acid amplification and real-time quantification for decentralized molecular diagnostics. The plasmonic real-time RT-PCR system features an ultrafast plasmonic thermocycler (PTC), a disposable plastic-on-metal (PoM) cartridge, and an ultrathin microlens array fluorescence (MAF) microscope. The PTC provides ultrafast photothermal cycling under white-light-emitting diode illumination and precise temperature monitoring with an integrated resistance temperature detector. The PoM thin film cartridge allows rapid heat transfer as well as complete light blocking from the photothermal excitation source, resulting in real-time and highly efficient PCR quantification. Besides, the MAF microscope exhibits close-up and high-contrast fluorescence microscopic imaging. All of the systems were fully packaged in a palm size for point-of-care testing. The real-time RT-PCR system demonstrates the rapid diagnosis of coronavirus disease-19 RNA virus within 10 min and yields 95.6% of amplification efficiency, 96.6% of classification accuracy for preoperational test, and 91% of total percent agreement for clinical diagnostic test. The ultrafast and compact PCR system can decentralize point-of-care molecular diagnostic testing in primary care and developing countries.

Conductive Silver/Carbon Fiber Films for Rapid Detection of Human Coronavirus

Polymerase chain reaction has gained attention since the outbreak of novel coronavirus in 2019. Due to its high specificity and capability for early detection, it is considered a standard method for the diagnosis of infectious diseases. However, the conventional thermocyclers used for nucleic acid amplification are not suitable for point-of-care testing applications, as they require expensive instruments, high-power consumption, and a long turnaround time. To suppress the widespread of the pandemic, there is an urgent need for the development of a rapid, inexpensive, and portable thermal cycler. Therefore, in this paper, we present a conductive silver/carbon fiber film-based thermal cycler with low power consumption (<5 W), efficient heating (~4.5 °C/s), low cost (<USD 200), and handheld size (11.5 × 7.1 × 7.5 mm). The conductive film, which was used as a heating source of the thermal cycler, was fabricated by the electrochemical deposition method. The successful coating of Ag was characterized by a scanning electron microscope and confirmed by energy-dispersive X-ray spectroscopy. The film showed excellent electrical/thermal conductivity and durability. Using our thermal cycler, 35 cycles of amplification were accomplished within 10 min. We also successfully demonstrated the multiplexed detection of various human coronaviruses (e.g., OC43, 229E, and NL63) using our thermal cycler.

A sample-to-answer DNA detection microfluidic system integrating sample pretreatment and smartphone-readable gradient plasmonic photothermal continuous-flow PCR

We report a microfluidic system integrating sample pretreatment and smartphone-readable gradient plasmonic photothermal continuous-flow PCR, paving the way for low-cost and rapid implementation of PCR diagnostics.