Fundamental Studies Of Nanomaterial-Mediated Photothermal Effects And Novel Applications In Visual Quantitative Disease Diagnoses

Infectious diseases and cancers frequently cause public health concerns and high burdens on health care globally. Early diagnosis of these diseases can provide an important guide on prevention, treatment, and prognosis in clinical practice. However, current laboratory diagnostic methods, such as nucleic acid- and protein-based detection methods, require sophisticated infrastructure, expensive and bulky instrumentation, well-trained personnel, and time-consuming processes, which significantly leads to high cost of detection assays and limit their wide accessibility, especially in low-resource settings. To address these issues, we have developed multiple simple, low-cost, and visual quantitative diagnostic methods based on nanomaterial-mediated photothermal effects for the detection of infectious diseases (tuberculosis and hepatitis C) and cancer (prostate cancer). Based on nanomaterial-mediated photothermal effects, quantitative disease diagnosis has been achieved by only using a common thermometer or a low-cost hybrid microfluidic device. On one aspect, photothermal effects have been conventionally applied in therapeutic strategies due to the unique property of converting photon energy to thermal energy; whereas, there are few reports regarding the quantitative biomolecular detection applications. In this Dissertation, we have studied the fundamentals of nanomaterial-mediated photothermal effects, established the photothermal biosensing principles, and explored their applications in quantitative disease diagnoses using a thermometer. On the other hand, microfluidic lab-on-a-chip (LOC) technology provides a great opportunity for biomolecular detection, with numerous benefits including low reagent consumption, miniaturization, and portability. Recently, hybrid microfluidic devices have great potential in the point-of-care (POC) diagnostic applications because of combining advantages from multiple chip substrates. Herein, we integrated the photothermal biosensing methods on hybrid microfluidic devices for quantitative diagnostics of both infectious diseases and cancers at the point of care. We, for the first time, developed a simple and universal photothermal biosensing method for the quantitative detection of Mycobacterium tuberculosis (MTB) DNA using a thermometer. By applying gold nanoparticle (AuNP) aggregation as a strong photothermal probe, the target nucleic acids were detected using an inexpensive thermometer upon the irradiation of a near-infrared (NIR) laser. High sensitivity was obtained with the limit of detection (LOD) of 0.28 nM, which was nearly 10-fold higher than that from a colorimetric method using a costly spectrometer. This method was further validated by testing various types of pathogenic nucleic acids, demonstrating its universality with good analytical recoveries while avoiding the use of bulky and expensive instrumentation. Furthermore, by using a simple paper/polymer hybrid microfluidic device, we, for the first time, developed a miniaturized, low-cost, and rapid quantitative method based on AuNP-mediated photothermal effects for the on-chip detection of MTB DNA using a thermometer. A simple one-step surface modification method was applied to immobilize DNA capture probes on paper, while the target MTB DNA was dual-hybridized with capture probes and AuNP-modified detector probes on the hybrid device. A strong photothermal agent, the oxidized TMB (3, 3, 5, 5-tetramethylbenzidine) (ox-TMB) was then produced from the AuNP-catalyzed reaction. Under the NIR laser irradiation for 3 min, this on-chip photothermal genetic analysis can be achieved using a thermometer, with higher sensitivity than conventional colorimetric methods while with no issues of color interference. In addition to genetic analyses, we also developed the photothermal applications in protein-based diagnostics. A low-cost and portable immunosensing method based on Fe3O4 NP-mediated photothermal effects was developed for the detection of the hepatitis C virus core antigen (HCVAg). Iron oxide nanoparticles were introduced in a conventional immunoassay (the direct ELISA (enzyme-linked immunosorbent assay)) and used as the peroxide-mimicking nanozymes to produce the photothermal probe, ox-TMB. Under the irradiation of a portable NIR laser, the photothermal detection of HCVAg was achieved using a common thermometer, demonstrating good analytical performance with high sensitivity and specificity, which were comparable to the results obtained from the commercial diagnostic kit using a bulky and expensive microplate reader. At last, we integrated the photothermal immunoassay with microfluidics and developed an immuno-PT-Chip (a photothermal effect-driven volumetric bar-chart immunosensing microchip) for visual quantitative detection of cancer biomarkers. In this strategy, Prussian blue nanoparticles (PB NPs) derived from a typical sandwich immunoassay served as a strong NIR photothermal probe. The immunosensing signals were converted to visual bar-chart movement distances on the immuno-PT-Chip due to heat generation and accumulation of vapor pressure under NIR laser irradiation. The quantitation of the target prostate-specific antigen (PSA) was achieved by directly recording the moving distance on the immuno-PT-Chip, without the aid of any bulky and expensive instruments or even a thermometer. High specificity and sensitivity were achieved with the LOD of 2.0 ng/mL, which met the requirement for clinical PSA testing. Good performance was verified by testing PSA in human serum and whole blood samples. The exploration of the immuno-PT-Chip provides significant advances for the POC diagnostic detection of biomarkers using microfluidics. In sum, we have established the photothermal detection principle for genetic analyses and immunoassays and developed different photothermal biosensing methods, in which low-cost POC detection of disease biomarkers has been achieved by simply using a common thermometer or low-cost hybrid microfluidic devices, alleviating the need for any bulky instruments and professional personnel. This Dissertation provides great potential for POC disease diagnosis based on nanomaterial-mediated photothermal effects and opens new possibilities in the development of simple, reliable, and low-cost disease diagnostic platforms, particularly in resource-poor settings with health system constraints