Keren Chen

Towards ultrasensitive malaria diagnosis using surface enhanced Raman spectroscopy

We report two methods of surface enhanced Raman spectroscopy (SERS) for hemozoin detection in malaria infected human blood. In the first method, silver nanoparticles were synthesized separately and then mixed with lysed blood; while in the second method, silver nanoparticles were synthesized directly inside the parasites of Plasmodium falciparum. It was observed that the first method yields a smaller variation in SERS measurements and stronger correlation between the estimated contribution of hemozoin and the parasitemia level, which is preferred for the quantification of the parasitemia level. In contrast, the second method yields a higher sensitivity to a low parasitemia level thus could be more effective in the early malaria diagnosis to determine whether a given blood sample is positive.

Sustained and Cost Effective Silver Substrate for Surface Enhanced Raman Spectroscopy Based Biosensing

While surface enhanced Raman spectroscopy (SERS) based biosensing has demonstrated great potential for point-of-care diagnostics in the laboratory, its application in the field is limited by the short life time of commonly used silver based SERS active substrates. In this work, we report our attempt towards SERS based field biosensing, involving the development of a novel sustained and cost-effective substrate composed of silver nanoparticles protected by small nitrogen-doped Graphene Quantum Dots, i.e. Ag NP@N-GQD, and its systematic evaluation for glucose sensing. The new substrate demonstrated significantly stronger Raman enhancement compared to pure silver nanoparticles. More importantly, the new substrate preserved SERS performance in a normal indoor environment for at least 30 days in both the wet and dry states, in contrast to only 10 days for pure silver nanoparticles. The Ag NP@N-GQD thin film in the dry state was then successfully applied as a SERS substrate for glucose detection in mouse blood samples. The new substrate was synthesized under mild experimental conditions, and the cost increase due to N-GQD was negligible. These results suggest that the Ag NP@N-GQD is a cost-effective and sustained SERS substrate, the development of which represents an important step towards SERS based field biosensing.

Review of Surface Enhanced Raman Spectroscopy for Malaria Diagnosis and a New Approach for the Detection of Single Parasites in the Ring Stage

Malaria is a global disease that desires early diagnosis in the field, for which one way is to detect hemozoin (a unique biomarker of malaria infection) at low concentrations. Moreover, many anti-malarial drugs inhibit the formation of hemozoin and facilitate toxic free heme stacking to kill malaria parasites. Therefore, monitoring hemozoin within malaria parasites is important to malaria diagnosis and drug development. Here, we first review various surface enhanced Raman spectroscopy-based techniques for malaria diagnosis. Then, to enable hemozoin detection in single parasites in the ring stage for the first time, we report a method based on surface enhanced Raman spectroscopy for hemozoin detection in Plasmodium falciparum in the ring stage. In this method, silver nanoparticles are directly synthesized within parasites after the lysis of red blood cells and parasites are confirmed to be in the ring stage by Giemsa staining after a special procedure of sample postprocessing. The Raman spectra of hemozoin acquired from parasites with silver nanoparticles synthesized inside are compared with those from parasites mixed with nanoparticles synthesized separately. The results confirm the feasibility of detecting hemozoin crystals within single parasites in the ring stage. This method offers a promising strategy to investigate the mechanism of heme metabolism in malaria infection and a tool to evaluate the effectiveness of anti-malaria drugs.

Surface enhanced Raman spectroscopy for malaria diagnosis and intradermal measurements

The biomarkers of many diseases such as malaria can be found in intradermal measurements. We will present two surface enhanced Raman spectroscopy (SERS) based methods for the detection of malaria biomarkers in blood, which are comparable to or outperform the standard clinical method. To eliminate the need of drawing blood, we will also report a stainless-steel microneedle based probe for direct intradermal SERS measurements. Moreover, we developed a deformable agarose needle to reduce the risk of sharp injury and cross contamination due to needle reuse. Tests in skin phantoms for glucose measurements demonstrated accuracy comparable to those traditional methods requiring blood drawing.

Corrigendum: Towards ultrasensitive malaria diagnosis using surface enhanced Raman spectroscopy.

Scientific Reports 6: Article number: 20177; published online: 09 February 2016; updated: 23 March 2017 In this Article, Yaw Aniweh and Peter Preiser are incorrectly listed as being affiliated with the ‘School of Chemical and Biomedical Engineering, Nanyang Technological University, Singapore 637457’.

Feasibility of quantitatively diagnosing cornea infection using Raman spectroscopy (Conference Presentation)

Ocular infection is a serious eye disease that could lead to blindness without prompt and proper treatment. In pathology, ocular infection is caused by microorganisms such as bacteria, fungi or viruses. The essential prerequisite for the optimal treatment of ocular infection is to identify the microorganism causing infection early as each type of microorganism requires a different therapeutic approach. The clinical procedure for identifying the microorganism species causing ocular infection includes Gram staining (for bacteria)/microscopy (for fungi) and the culture of corneal surface scraping, or aqueous and vitreous smear samples taken from the surface of infected eyes. The culture procedure is labor intensive and expensive. Moreover, culturing is time consuming, which usually takes a few days or even weeks. Such a long delay in diagnosis could result in the exacerbation of patients’ symptoms, the missing of the optimal time frame for initiating treatment and subsequently the rising cost for disease management. Raman spectroscopy has been shown highly effective for non-invasive identification of both fungi and bacteria qualitatively. In this study, we investigate the feasibility of identifying the microorganisms of ocular infection and quantifying the concentrations using Raman spectroscopy by measuring not only gram negative and gram positive bacteria but also infected cornea. By applying a modified orthogonal projection approach, the relative concentration of each bacteria species could be quantified. Our results indicate the great potential of Raman spectroscopy as an alternative tool for non-invasive diagnosis of ocular infection and could play a significantly role in future ophthalmology.

Raman spectroscopy for discrimination of neural progenitor cells and their lineages (Conference Presentation)

Neurological diseases are one of the leading causes of adult disability and they are estimated to cause more deaths than cancer in the elderly population by 2040. Stem cell therapy has shown great potential in treating neurological diseases. However, before cell therapy can be widely adopted in the long term, a number of challenges need to be addressed, including the fundamental research about cellular development of neural progenitor cells. To facilitate the fundamental research of neural progenitor cells, many methods have been developed to identify neural progenitor cells. Although great progress has been made, there is still lack of an effective method to achieve fast, label-free and noninvasive differentiation of neural progenitor cells and their lineages. As a fast, label-free and noninvasive technique, spontaneous Raman spectroscopy has been conducted to characterize many types of stem cells including neural stem cells. However, to our best knowledge, it has not been studied for the discrimination of neural progenitor cells from specific lineages. Here we report the differentiation of neural progenitor cell from their lineages including astrocytes, oligodendrocytes and neurons using spontaneous Raman spectroscopy. Moreover, we also evaluate the influence of system parameters during spectral acquisition on the quality of measured Raman spectra and the accuracy of classification using the spectra, which yield a set of optimal system parameters facilitating future studies.

Nitrogen doped graphene quantum dots effectively preserve the surface enhancement performance of silver nanoparticles (Conference Presentation)

In this work, we report a novel substrate for surface enhanced Raman spectroscopy (SERS) composed of silver nanoparticles protected by small nitrogen-doped Graphene Quantum Dots, i.e. Ag NPs-N-GQDs, synthesized under mild experimental conditions, which can preserve the SERS performance in normal indoor environment for up to 30 days. The field emission scanning electronic microscope (FESEM) images confirm that the N-GQDs play a significant role in the control of metallic nanoparticles morphology. The X-ray photoelectron spectroscopy (XPS) result clearly indicates the N-GQDs was successfully immobilized on the surface of silver nanoparticles (Ag NPs). Ag NPs-N-GQDs demonstrated Raman enhancement stronger than pure Ag NPs likely due to an increase in the number of the “hotspots” formed by coupled nanostructures. N-GQD protected Ag NPs were evaluated in SERS measurements of R6G when they were made fresh and have been stored in normal indoors condition for up to 30 days. Then Ag NPs-N-GQDs were used as a SERS substrate for glucose detection. The linearity range of glucose was found to be ranged from 1 μM to 1 M with a detection limit of 0.1 μM in glucose solutions. It was also applied successfully for glucose detection in rat blood samples. The present study demonstrates that the novel Ag NPs−N-GQDs nanostructure has great potential to be used as a cost effective sustained SERS substrate, which can be extremely useful in the wide adoption of SERS based sensors.

Ultrasensitive surface-enhanced Raman spectroscopy for malaria diagnosis

Malaria is a global infectious disease that causes 438,000 deaths a year around the world.1 As the malarial infection can induce death soon after the appearance of the first symptoms, rapid and early diagnosis is an important part of the control and treatment of the disease. At present, microscopic examination of Giemsa-stained blood smears is considered the ‘gold standard’ for malaria diagnosis. This process, however, is time-consuming, and it requires the use of a central laboratory and skilled operators (especially problematic in low-resource regions). To overcome these problems, several other methods for malaria diagnosis have been developed. These include flow cytometry,2 rapid diagnostic tools,3 the quantitative buffy coat method,4 and the polymerase chain reaction (PCR).5 Although these methods have made a significant contribution to the field of malaria diagnosis, most of them suffer from low sensitivity, high cost, or complicated sample preparation. In addition, the use of Raman spectroscopy has shown great potential for the detection of hemozoin (a unique biomarker of malaria parasites during the early stage of infection).6 The sensitivity levels of such Raman spectroscopy techniques (including conventional surface-enhanced Raman spectroscopy7), however, are insufficient to realize early malaria diagnosis. In our work,8 we have therefore been developing ways to further enhance the sensitivity of surface-enhanced Raman spectroscopy (SERS) for malaria detection. With our ultrasensitive SERS techniques we can facilitate diagnosis during the early stages of infection (i.e., when the hemozoin level is very low). In our approach, we enhance the Raman signal (by several orders of magnitude) by binding the analyte molecule (hemozoin) to SERS-sensitive nanostructures or nanoparticles (made of noble metals such as silver). The precise enhancement factor Figure 1. Surface-enhanced Raman spectroscopy (SERS) spectra of ˇhematin that were obtained with (top) and without (bottom) the use of the magnetic-field enhancement methodology. Spectra are shown for ˇ-hematin mixed with (a) and (d) iron oxide–silver (Fe3O4@Ag) nanoparticles, without any nanoparticles (b) and (e), and (c) and (f) with Fe3O4 nanoparticles. PEx: Excitation power. a.u.: Arbitrary units.

Investigation of surface enhanced Raman spectroscopy for hemozoin detection in malaria diagnosis

We report two methods of surface enhanced Raman spectroscopy (SERS) for hemozoin detection in malaria infected human blood. In the first method, silver nanoparticles were synthesized separately and then mixed with lysed blood; while in the second method, silver nanoparticles were synthesized directly inside the parasites of Plasmodium falciparum.