The revealing aspect of qualitative and quantitative presence of biological markers alongside other analytes, including DNA, proteins, and carbohydrates, can indicate disease states and physiological progressions. Sensitive and accurate detection of these at low levels has the unique advantage of potentially being used for identifying the earliest sign of disease [[1], [2], [3], [4]]. The DNA concentration in human plasma/serum may be an indicator of many tumours, DNA detection in urine may aid in the early diagnosis of cancer, TB, HIV, malaria, and other disorders [5,6]. Hence, for disease diagnosis, quick and specific identification of DNA can affect accuracy, specificity, expenses, accessibility, and clinical outcomes. So far, various techniques have been developed for the sensing of DNA such as electroluminescence, fluorescence, and electrochemical methods [[7], [8], [9], [10]]. Among them fluorescence-based sensing of DNA has been mostly preferred due to its high accuracy, sensitivity, repeatability, and simplicity [7,[11], [12], [13]]. Hence, currently, fluorescent nanomaterials have been widely used in order to fabricate lucid biological nano-sensors for the detection of biological species due to their exceptional optical properties and excellent chemical sensing performances [4,7,14,15]. There are mainly two approaches used in fluorescence-based sensing methods on is “fluorescence quenching” (turn off method) other is “fluorescence enhancement” (turn on methos). The analysis of analytes can be easily carried out by turn off method, but false positive result may occur due to disturbance of another quencher instead of analyte, instead of turn off method turn on method provide more reliable results and also prevent from false results [5].

In recent years, the development of lanthanide-based luminescent sensors for the sensing of biomolecules has attracted researchers. Lanthanoid doped nanomaterials sensor is one of prime and popular fluorescence specified optical sensor due to its advantages of good fluorescence efficiency, sharp and intense spectra, wide absorption ranges, long fluorescence lifetime, tuning of excitation wavelength, high sensitivity, selectivity and lower limited of detection and wide range applications [7,[13], [14], [15], [16], [17]]. These properties of lanthanides emanate from the intra configurational 4f electronic transitions of Ln3+ ions. The 4f-4f transitions are basically electric dipole transitions and magnetic dipole transitions forbidden by Laporte selection rule [7]. Thus, the direct excitation of lanthanoids is mostly inefficient but can be enhanced with the attachment of light harvesting chromophore which lead to the improved absorption of light, and transfer energy to lanthanoids through ‘antenna effect’, thereby, resulting in intense luminescence [7,15,18]. Despite of these, the lanthanoids based materials are usually insoluble, and unstable in the aqueous medium, less biocompatible, and get excited with the short wavelength light sources such as ultra -violet light limit the biological applications by causing the photo damage to cells and thus hinders the practical utility of the sensors for fluorescence measurements [5,19,20]. Hence, it is significant to devolve a novel lanthanide complex with desired features in order to overcome these limitations.

Nowadays, lanthanide-doped core-shell nanophosphors have drawn adequate research initiatives in the sensor research field because of their biocompatible, functional, and tuneable optical properties that are derived from their core and shell materials, flexible thicknesses, shapes, and sizes [15,21]. So far, a huge number of soft and hard materials has been used as a strategical approach to construct the core shell structures. One of these is a silica (SiO2)-coated structure that has often been used due to its nano porous, good thermal and chemical stability, tuneable sizes, and optical transparency [22,23]. Moreover, silica enhances the brightness and resolution by reducing scattering of light as compared to the conventional materials. It contains hydroxyl groups (-OH), which increases its potential applicability for biomedical and optoelectronic applications [22,24]. Formation of the core-shell might improve the optical property but mere presence of -OH group on the surface of silica is not only adequate for biomedical applications [14,15]. Hence, it is important to functionalize the surface of the core shell with the material having active functional groups to increase photo stability, water solubility and easy conjunction with biomolecules.

Chitosan is one of the abundantly available natural bio polymers derived from chitin found in the shells of crustaceans [[25], [26], [27], [28]]. It shows certain interesting properties such as biodegradable, hydrophilic nature, bio-functional, low cost, and easy functionalization. Besides, chitosan has amino and hydroxyl groups which are helpful to functionalize biomolecules [14,[25], [26], [27]]. Under this framework, we delineate a simple approach for the synthesis of chitosan functionalized lanthanoid based core shell (Ca-Eu: Y2O3@SiO2) nanophosphor for the sensitive and specific detection/determination of dsDNA biomarker as a “turn on” sensor.

In present work we have reported a simple method for the synthesis of chitosan functionalized Lanthanoid based core shell (Ca-Eu:Y2O3@SiO2) phosphor. The synthesized chitosan functionalized Ca-Eu:Y2O3@SiO2 phosphor has been characterized for its structural, morphology and optical properties in detail. The chitosan functionalized Ca-Eu:Y2O3@SiO2 phosphor contains hydroxyl, and amino groups which coordinate with the dsDNA and causes fluorescence enhancement and act as “turn on” sensor. The ratio of fluorescence intensity enhancement of phosphor is proportional to the concentration of dsDNA. To best of our knowledge, chitosan functionalized Ca-Eu:Y2O3@SiO2 nanophosphor has been used for the first time for fluorescence sensing of dsDNA.