Associate Professor XU Qing-Hua

B.Sc, Zhejiang Univ.; M.Sc., Peking Univ. & Univ. of Chicago; Ph.D., UC Berkeley; Postdoctoral, Stanford & UC Santa Barbara

Contact Information

Department of Chemistry, NUS 
3 Science Drive 3 
Singapore 117543 
Office: S8-02-05C
Tel: (65) 6516-7880
Fax: (65) 6779-1691

Research Interests

Research Areas: Materials Physics and Chemistry/ Nanomaterials and Nanophotonics/ Optical Materials/ Optical Spectroscopy and Imaging

The research in our group mainly focuses on novel nanocomposite materials and their linear and nonlinear optical properties as well as their applications in imaging, sensing, biomedicine, energy and environmental areas. Our research spans a broad range from materials preparation, fundamental understanding and practical applications.

i). Nanocomposites with enhanced optical properties

Fig 1

Various nanocomposites containing noble metals and organic materials are prepared to investigate their optical properties, such as enhanced fluorescence, two-photon excitation and Raman scattering using various novel optical spectroscopy and imaging techniques. Their applications in bio-imaging, sensing, biomedicine, optoelectronics and photo-catalysis (water splitting and organic waste treatment) are also being explored. 

ii). Conjugated polymers and their applications

Fig 2

Conjugated organic materials, such as conjugated polymers and oligomers, have many interesting optical and electronic properties and thus many promising applications. Understanding their optical properties is not only fundamentally important, but also vital for the application of these materials. Due to their exceptional properties, conjugated materials can function as light-harvesting complex to significantly enhance the optical properties of nearby molecules by energy transfer. We will develop various conjugated polymer based platforms for applications in bio-sensing, bio-imaging, biomedicine and optoelectronic devices.

iii). Optical spectroscopy and imaging


Our group is consistently developing various novel spectroscopy and imaging techniques, in particular those related with femtosecond lasers. We are developing various techniques such as transient absorption (pump probe), time-resolved fluorescence, z-scan, multi-photon excitation fluorescence microscopy, fluorescence lifetime imaging microscopy (FLIM), single particle spectroscopy, and time-gated detections. These novel techniques will be used to understand the photo-physics of various nanocomposite and organic materials in solution and in films, and in device structures.

Representative Publications

(click here for a complete list of publications)

  1. X.-F. Jiang, L. Polavarapu,S.T. Neo, T. Venkatesan, and Q.-H. Xu*, "Graphene Oxides as Tunable Broadband Nonlinear Optical Materials for Femtosecond Laser Pulses", J. Phys. Chem. Lett., 2012, 3 (6), 785-790.

  2. X.Q. Shen, L. Li, H. Wu, S. Q. Yao, and Q.-H. Xu , "Photosensitizer-Doped Conjugated Polymer Nanoparticles for Simultaneous Two-photon Imaging and Two-photon Photodynamic Therapy in Living Cells", Nanoscale, 2011, 3 (12), 5140.

  3. L. Polavarapu, K.K. Manga,H.D. Cao, K.P. Loh, Q.-H. Xu, "Preparation of Conductive Silver Films at Mild Temperatures for Printable Organic Electronics", Chem. Mater., 2011, 23, 3273.

  4. L. Polavarapu, K.K. Manga, Y. Kuai, P.K. Ang, H.D. Cao, J. Balapanuru, K.P. Loh, Q.-H. Xu, "Alkylamine Capped Metal Nanoparticle Inks for Printable SERS Substrates, Electronics and Broadband Photon Detectors", Nanoscale, 2011, 3(5), 2268.

  5. M. D. Regulacio, C. Ye, S.H. Lim, M. Bosman, L. Polavarapu, Q.-H. Xu, M.-Y. Han, "One-Pot Synthesis of Cu1.94S-CdS and Cu1.94S-ZnxCd1-xS Nanodisk Heterostructures",J. Am. Chem. Soc., 2011, 133 (7), 2052-2055.

  6. Z.P. Guan, L. Polavarapu, Q.-H. Xu,"Enhanced Two-photon Emission in Coupled Metal Nanoparticles Induced by Conjugated Polymers", Langmuir, 2010, 26 (23), 18020-18023.

  7. T.T. Zhao, H. Wu, S.Q. Yao, Q.-H. Xu, and G.Q. Xu, "Nanocomposites Containing Gold Nanorods and Porphyrin Doped Mesoporous Silica with Dual Capability of Two-photon Imaging and Photodynamic Therapy", Langmuir, 2010, 26(18), 14937-14942.

  8. X.S. Ren and Q.-H. Xu, "Label Free DNA Sequence Detection with Enhanced Sensitivity and Selectivity using Cationic Conjugated Polymers and PicoGreen", Langmuir, 2009, 25(1), 43-47.

  9. N. Tian and Q.-H. Xu, "Enhanced Two-Photon Excitation Fluorescence by Fluorescence Resonance Energy Transfer Using Conjugated Polymers", Adv. Mater., 2007, 19(15), 1988 (Featured in "Advances in Advance").

  10. D. Cheng and Q.-H. Xu, "Separation Distance Dependent Fluorescence Enhancement of Fluorescein Isothiocyanate by Silver Nanoparticles", Chem. Commun, 2007, No.3, 248-250.

  11. Qing-Hua Xu, Shu Wang, A. Mikhailovsky, Guillermo C. Bazan, Daniel Moses and Alan J. Heeger, "Fluorescence Resonance Energy Transfer Gate in DNA Sequence Detection: a Time-Resolved Study", PNAS, 2005(3), 530.

  12. Qing-Hua Xu, Brent S. Gaylord, Shu Wang, Guillermo C. Bazan, Daniel Moses and Alan J. Heeger, "Time-resolved energy transfer in DNA sequence detection using water-soluble conjugated polymers: the role of electrostatic and hydrophobic interactions", PNAS, 2004, 101(32), 11634.